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1

NEGATIVE CHEMICAL IONIZATION STUDIES OF HUMAN AND FOOD CHAIN CONTAMINATION WITH XENOBIOTIC CHEMICALS  

EPA Science Inventory

Negative chemical ionization mass spectrometry with a mixture of isobutane, methylene chloride, and oxygen as the reagent gas has been used to explore contamination of environmental substrates with xenobiotic chemicals. The substrates in question, fish tissue, human seminal plasm...

2

PENTACHLOROPHENOL IN THE ENVIRONMENT: EVIDENCE FOR ITS ORIGIN FROM COMMERCIAL PENTACHLOROPHENOL BY NEGATIVE CHEMICAL IONIZATION MASS SPECTROMETRY  

EPA Science Inventory

Commercial pentachlorophenol (PCP) contains significant quantities of tetrachlorophenol (TCP). The occurrence of TCP in environmental samples provides a chemical marker for PCP originating from commercial formulations. Negative chemical ionization mass spectrometry has been used ...

3

PENTACHLOROPHENOL IN THE ENVIRONMENT. EVIDENCE FOR ITS ORIGIN FROM COMMERCIAL PENTACHLOROPHENOL BY NEGATIVE CHEMICAL IONIZATION MASS SPECTROMETRY  

EPA Science Inventory

Commercial pentachlorophenol (PCP) contains significant quantities of tetrachlorophenol (TCP). The occurrence of TCP in environmental samples provides a chemical marker for PCP originating from commercial formulations. Negative chemical ionization mass spectrometry has been used ...

4

Applications of a versatile technique for trace analysis: atmospheric pressure negative chemical ionization.  

PubMed Central

The ability to use ambient air as a carrier and reagent gas in an atmospheric pressure chemical ionization source allows instantaneous air analysis to be combined with hypersensitivity toward a wide variety of compounds. The TAGA (Trace Atmospheric Gas Analyser) is an instrument which is designed to use both positive and negative atmospheric pressure chemical ionization (APCI) for trace gas analysis; this paper describes several applications of negative APCI which demonstrates that the technique is not limited to environmental monitoring. Examples are described which suggest that the TAGA can be used for the detection of illicit drugs and explosives, and for the analysis of breath or skin emissions, as well as for air pollution measurements. The applications are not restricted by the use of ambient air as a reagent gas; addition to the air carrier of various gases allows specific reagent ions such as Cl- or Br- to be generated. Furthermore, in certain situations pure gas carriers can be used to provide even more flexibility in the ion chemistry, with a short term absorber-desorber system used to transfer the sample from the ambient air into the ion source region. The potential uses for APCI are expanding continuously as the understanding of the complex ion-molecule chemistry grows. This paper underlines the complementary relation between the development of new negative chemical ionization (NCI) techniques and practical applications using the TAGA system. PMID:6775945

Thomson, B A; Davidson, W R; Lovett, A M

1980-01-01

5

Isotope effect in negative ion chemical ionization mass spectrometry of deuterium labelled lormetazepam.  

PubMed

This study identified the reason for the poor quantification of lormetazepam-TMS (1) using negative ion chemical ionization with lormetazepam-1,1,1-2H3-TMS (2) as an internal standard. Mass spectra of lormetazepam and its deuterium labelled compounds determined at various ion source temperatures (100-250 degrees C) gave almost the same behaviour for 1 and lormetazepam-3',4',5',6'-2H4-TMS (3) but a different one for 2, suggesting that the poor quantification was due to an isotope effect. This was confirmed by the findings that the ratios of ion currents of the base peaks of 1 and 3 were independent of the ion source temperature but those of 1 and 2 varied markedly with it. This phenomenon was also observed in the mass fragmentography of the molecular ion, although to a lesser degree than that of the above fragment. In both positive ion chemical ionization and electron impact ionization modes, no isotope effect arose because there was no corresponding fragment to cause the isotope effect. PMID:2955830

Takahashi, S

1987-06-01

6

Determination of BROMATE AT PARTS-PER-TRILLION LEVELS BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY WITH NEGATIVE CHEMICAL IONIZATION  

EPA Science Inventory

The ozonation of bromide-containing source waters produces bromate as a class 2B carcinogenic disinfection by-product. The present work describes the determination of bromate by gas chromatography-negative chemical ionization mass spectrometry (GC-NCIMS) following a bromate react...

7

Characterization of a novel diclofenac metabolite in human urine by capillary gas chromatography-negative chemical ionization mass spectrometry  

Microsoft Academic Search

A sensitive analytical method was developed to characterize diclofenac metabolites in small amounts of body fluids. Desalted and lyophilized urine samples were extracted with supercritical carbon dioxide directly or after acidic hydrolysis. The extracts were derivatized with N-tert.-butyldimethylsilyl-N-methyltrifluoroacetamide. The derivatives were separated by capillary gas chromatography and identified by negative chemical ionization mass spectrometry. Full mass spectra were obtained at

Wolfgang Blum; Johann W. Faigle; Ulrike Pfaar; Alfred Sallmann

1996-01-01

8

An Ultra-Trace Analysis Technique for SF6 Using Gas Chromatography with Negative Ion Chemical Ionization Mass Spectrometry.  

PubMed

Sulfur hexafluoride (SF6) is widely used as a tracer gas because of its detectability at low concentrations. This attribute of SF6 allows the quantification of both small-scale flows, such as leakage, and large-scale flows, such as atmospheric currents. SF6's high detection sensitivity also facilitates greater usage efficiency and lower operating cost for tracer deployments by reducing quantity requirements. The detectability of SF6 is produced by its high molecular electronegativity. This property provides a high potential for negative ion formation through electron capture thus naturally translating to selective detection using negative ion chemical ionization mass spectrometry (NCI-MS). This paper investigates the potential of using gas chromatography (GC) with NCI-MS for the detection of SF6. The experimental parameters for an ultra-trace SF6 detection method utilizing minimal customizations of the analytical instrument are detailed. A method for the detection of parts per trillion (ppt) level concentrations of SF6 for the purpose of underground ventilation tracer gas analysis was successfully developed in this study. The method utilized a Shimadzu gas chromatography with negative ion chemical ionization mass spectrometry system equipped with an Agilent J&W HP-porous layer open tubular column coated with an alumina oxide (Al2O3) S column. The method detection limit (MDL) analysis as defined by the Environmental Protection Agency of the tracer data showed the method MDL to be 5.2 ppt. PMID:25452581

Jong, Edmund C; Macek, Paul V; Perera, Inoka E; Luxbacher, Kray D; McNair, Harold M

2014-12-01

9

Fast gas chromatography negative chemical ionization tandem mass spectrometry of explosive compounds using dynamic collision-induced dissociation  

NASA Astrophysics Data System (ADS)

The analysis of nine explosive compounds by gas chromatography tandem mass spectrometry (GC-MS/MS) using negative chemical ionization (NCI) was performed under two different conditions: first, a conventional GC separation coupled with a standard ion dissociation method in a quadrupole ion trap (QIT) was performed in segmented selected reaction monitoring mode; second, a fast GC separation on a microbore capillary column was combined with a faster method of collisional activation in ion traps wherein fragmentation is deliberately accomplished during the mass acquisition scan. The conventional GC-MS/MS method provided separation times in 10 min with detection limits between 0.8 and 280 pg on column. The fast GC method with dynamic collision-induced dissociation (DCID) offered a confirmatory method for the analysis of high explosives with separation times under 2.5 min and detection limits between 0.5 and 5 pg on column, without any hardware modifications to the instrument. The implementation of DCID in combination with three-times-faster mass scanning allows the acquisition of tandem mass spectra to at least 5 Hz (while averaging three scans per spectrum). Although detection limits for GC-NCI-MS/MS using conventional CID or DCID are not quite on par with LODs achieved by GC-ECD, the combination of NCI with DCID tandem MS leads to detection limits at least comparable, if not superior, to other mass spectrometric methods. Selected reaction monitoring in the negative ionization mode is anticipated to offer the most selective approach to detecting explosives and eliminating potential interferences, which could ultimately lead to the best detection limits for real, contaminated samples.

Collin, Olivier L.; Zimmermann, Carolyn M.; Jackson, Glen P.

2009-01-01

10

MICROMETHODS FOR TOXIC RESIDUE SCREENING BY NEGATIVE CHEMICAL IONIZATION MASS SPECTROMETRY  

EPA Science Inventory

Methods were developed for the analysis of polychlorinated chemical residues found in milligram quantities of biological samples. Sample preparation by micro-continuous liquid-liquid extraction steam distillation or by micro gel-permeation chromatography gave sufficiently clean r...

11

Quantification of lorazepam and lormetazepam in human breast milk using GC-MS in the negative chemical ionization mode.  

PubMed

Lormetazepam (Loramet is a benzodiazepine mainly used as an hypnotic to treat insomnia. Lorazepam (Temesta) is used as an anxiolytic, tranquilizer, sedative, and anticonvulsant, and it is the major metabolite of lormetazepam. In this study, we designed a method to simultaneously detect and quantify these substances in human breast milk. Solid-phase extraction of 2 mL of milk was followed by derivatization with a trimethylsilyl reagent. Separation and detection was performed using gas chromatography coupled to mass spectrometry in the negative chemical ionization mode. Calibration curves were linear in the ranges of 10-200 and 1-20 ng/mL for lorazepam and lormetazepam, respectively. Limits of detection were estimated at 0.016 ng/mL for lormetazepam and 0.100 ng/mL for lorazepam. Our method was applied to real case samples from a woman receiving both benzodiazepines. Lorazepam concentrations varied from 55.3 to 123.1 ng/mL, and lormetazepam concentrations varied from 1.7 to 7.3 ng/mL. PMID:17555647

Lemmer, Patrick; Schneider, Serge; Mühe, Annette; Wennig, Robert

2007-05-01

12

Effect of high-performance liquid chromatography mobile phase components on sensitivity in negative atmospheric pressure chemical ionization liquid chromatography-mass spectrometry.  

PubMed

We have investigated the effect of several common buffers (10-mM formic acid, 10-mM ammonium acetate, and 100-mM ammonium acetate) on the ionization of a series of model compounds that are amenable to negative atmospheric pressure chemical ionization to determine the extent of ionization quenching that can occur. In addition, we have compared the sensitivity of these standard mobile phases to a mobile phase that does not contain an acidic buffer component, but rather a base (N-methylmorpholine). The results showed that, as expected, the sensitivity for the test analytes was greatest in the mobile phase that lacked acidic components. In general, ionization of analytes that contained a single, more weakly acidic functional group was inhibited to a greater degree by more strongly acidic buffer components. In some cases, ionization was quenched completely by acidic buffer components, Ionization of compounds that were more strongly acidic was quite good in all mobile phases tested. Differences in the ionization efficiencies of the analytes in each mobile phase were correlated with the gas-phase reagent ions present. As a point of reference, each of the analytes also was analyzed in the positive ion mode and the signal intensities were compared to those obtained in the negative ion mode. In addition, the utility of mobile phases that contained N-methylmorpholine for chromatographic separations was demonstrated. PMID:24202887

Schaefercor, W H; Dixon, F

1996-10-01

13

Formation and reactions of negative ions relevant to chemical ionization mass spectrometry. I. Cl mass spectra of organic compounds produced by F? reactions  

PubMed Central

A systematic study of the negative-ion chemical ionization mass spectra produced by the reaction of F? with a wide variety of organic compounds has been accomplished. A time-of-flight mass spectrometer fitted with a modified high pressure ion source was employed for these experiments. The F? reagent ion was generated from CF3H or NF3, typically at an ion source pressure of 100 ?m. In pure NF3, F? is the major ion formed and constitutes more than 90% of the total ion intensity. While F? is also the major primary ion formed in pure CF3H, it undergoes rapid ion-molecule reactions at elevated source pressures, yielding (HF)nF? (n = 1?3) ions, which makes CF3H less suitable as a chemical ionization reagent gas. Among the organic compounds investigated were carboxylic acids, ketones, aldehydes, esters, alcohols, phenols, halides, nitriles, nitrobenzene, ethers, amines and hydrocarbons. An intense (M ? 1)? ion was observed in the F? chemical ionization mass spectra of carboxylic acids, ketones, aldehydes and phenols. Alcohols yield only (M + F)? ions upon reaction with F?. A weaker (M + F)? ion was also detected in the F? chemical ionization spectra of carboxylic acids, aldehydes, ketones and nitriles. The F? chemical ionization mass spectra of esters, halides, nitriles, nitrobenzene and ethers are characterized primarily by the ions, RCOO?, X?, CN?, NO2?, and OR?, respectively. In addition, esters show a very weak (M ? 1)? ion (except formates). In the F? chemical ionization spectra of some aliphatic alkanes and o-xylene, a very weak (M + F)? ion was observed. Amines and aliphatic alkenes exhibit only insignificant fragment ions under similar conditions, while aromatic hydrocarbons, such as benzene and toluene are not reactive at all with the F? ion. The mechanisms of the various reactions mentioned are discussed, and several experimental complications are noted. In still other studies, the effects of varying several experimental parameters, including source pressure, relative proportions of the reagent and analyte, and other ion source parameters, on the observed chemical ionization mass spectra were also investigated. In a mixture of NF3 and n-butanol, for example, the ratio of the intensities of the ions characteristic of the alcohol to that of the (HF)nF? ion was found to decrease with increasing sample pressure, with increasing NF3 pressure, and with increasing electron energy. No significant effects on the spectra were observed to result from variation of the source repeller field or the source temperature. The addition of argon to the source as a potential moderator did not alter the F? chemical ionization spectrum significantly, but the use of oxygen appears to inhibit formation of the (HF)nF? cluster ion. The advantages of using F? as a chemical ionization reagent are discussed, and comparisons are made with other reagent ions. PMID:7428746

Tiernan, T. O.; Chang, C.; Cheng, C. C.

1980-01-01

14

Determination of deltamethrin in rat plasma and brain using gas chromatography-negative chemical ionization mass spectrometry.  

PubMed

Quantification of the pyrethroid deltamethrin (DLM) in small (100 ?L) biological samples from rodents is essential for toxicokinetic studies of trace levels of the insecticide in foods. Such empirical kinetic data are necessary for construction of valid physiologically-based toxicokinetic models. There are no validated methods in the literature for determining deltamethrin in 100 ?L plasma and brain samples. Plasma and brain samples were stabilized using sodium fluoride as an esterase inhibitor, and the DLM was extracted by protein precipitation using acetonitrile and phosphoric acid. The samples were vortexed, centrifuged, evaporated to dryness, and reconstituted in toluene prior to injection into a gas chromatograph equipped with a quadrupole mass analyzer. Samples were ionized via electron capture in the negative ion mode using methane, and the molecular ion and fragment ions of DLM were monitored using Selected-Ion Monitoring (SIM) for quantitation and verification of the analyte. Cis-permethrin was used as the internal standard for the method, which was validated according to current US FDA guidelines. Linearity was determined between 0.3 and 1,000 ng/mL, with a limit of detection of 150 pg/mL. The intra- and inter-batch variation for precision (as % relative standard deviation, RSD) and accuracy (as % bias) of the method were better than 20% at the limit of quantitation and better than 15% across the remaining linear range (n=18), with recoveries of 113% and 68% for plasma and brain respectively. Benchtop stability, autosampler stability, and freeze/thaw stability studies of the method (over a 3-day freeze/thaw cycle) were found to be within the acceptance criteria of 20% RSD and bias. This optimized method was applied to the quantitation of DLM in plasma and brain homogenate samples obtained up to 12h after oral dosing of Sprague-Dawley rats with 1mg DLM/kg body weight. PMID:24814001

Gullick, Darren; Popovici, Andrew; Young, Holly C; Bruckner, James V; Cummings, Brian S; Li, Pei; Bartlett, Michael G

2014-06-01

15

Negative ion chemical ionization gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry of prostanoid pentafluorobenzyl ester/methoxime/trimethylsilyl ether derivatives.  

PubMed

Negative ion chemical ionization mass spectra of prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2, 6-oxo-prostaglandin F1 alpha, 2,3-dinor-6-oxo-prostaglandin F1 alpha, thromboxane B2, 2,3-dinor-thromboxane B2, and 11-dehydro-thromboxane B2 pentafluorobenzyl ester (PFB)/methoxime/trimethylsilyl ether derivatives are presented. Collisionally activated decomposition mass spectra of the [M-PFB]- ions at collision energies of 8-24 eV and argon collision gas pressures of 1-2m Torr almost show only fragmentation of trimethylsilanol, (CH3)2Si = CHOH, (CH3)2Si = CH2 and methanol whereas, except for carbon dioxide loss, only few low-intensity fragments from the carbon skeleton of the prostanoids are observed. PMID:3365491

Schweer, H; Seyberth, H W; Meese, C O; Fürst, O

1988-02-01

16

Comparison of negative-ion proton-transfer with iodide ion chemical ionization mass spectrometry for quantification of isocyanic acid in ambient air  

NASA Astrophysics Data System (ADS)

Isocyanic acid (HNCO) is a trace gas pollutant of potential importance to human health whose measurement has recently become possible through the development of negative-ion proton-transfer chemical ionization mass spectrometry (NI-PT-CIMS) with acetate reagent ion. In this manuscript, an alternative ionization and detection scheme, in which HNCO is quantified by iodide CIMS (iCIMS) as a cluster ion at m/z 170, is described. The sensitivity was inversely proportional to water vapor concentration but could be made independent of humidity changes in the sampled air by humidifying the ion-molecule reaction (IMR) region of the CIMS. The performance of the two ionization schemes was compared and contrasted using ambient air measurements of HNCO mixing ratios in Calgary, AB, Canada, by NI-PT-CIMS with acetate reagent ion from Dec 16 to 20, 2013, and by the same CIMS operated in iCIMS mode from Feb 3 to 7, 2014. The iCIMS exhibited a greater signal-to-noise ratio than the NI-PT-CIMS, not because of its sensitivity, which was lower (?0.083 normalized counts per second (NCPS) per parts-per-trillion by volume (pptv) compared to ?9.7 NCPS pptv-1), but because of a much lower and more stable background (3 ± 4 compared to a range of ?2 × 103 to ?6 × 103 NCPS). For the Feb 2014 data set, the HNCO mixing ratios in Calgary air ranged from <12 to 94 pptv (median 34 pptv), were marginally higher at night than during day, and correlated with nitrogen oxide (NOx = NO + NO2) mixing ratios and submicron particle volume. The ratios of HNCO to NOx observed are within the range of emission ratios reported for gasoline-powered motor vehicles.

Woodward-Massey, Robert; Taha, Youssef M.; Moussa, Samar G.; Osthoff, Hans D.

2014-12-01

17

Determination of microbial fatty acid profiles at femtomolar levels in human urine and the initial marine microfouling community by capillary gas chromatography-chemical ionization mass spectrometry with negative ion detection  

Microsoft Academic Search

Summary Room temperature esterification with the electron capturing pentafluorobenzyl bromide in glass capillaries, with analysis by capillary gas-liquid chromatography coupled with chemical ionization mass spectrometry and negative ion detection in the selected ion mode, allowed detection and identification of fatty acids from micro- bial biofilms at the femtomolar level. This sensitivity was achieved without loss of specificity of the mass

Goran Odham; Anders Tunlid; Gunilla Westerdahl; Lennart Larsson; James B. Guckert; David C. White

1985-01-01

18

[Determination of polybrominated diphenyl ethers in indoor dust using ultrasonic-assisted extraction and gas chromatography-negative chemical ionization mass spectrometry].  

PubMed

A method for the determination of eight polybrominated diphenyl ethers (PBDEs) in indoor dust was developed. A vacuum cleaner was used for gathering the house dust, and n-hexane was added and the extraction was performed in an ultrasonic bath. The supernatant was concentrated and then n-hexane was added to 0.1 mL. Gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS) has been investigated for the determination of the eight PBDE congeners in indoor dust. The eight PBDEs were separated within 20 min. The absolute recoveries were 53.2% - 107.6%. The relative standard deviations (RSDs) of intra-day were between 2.8% and 16.5%, while the RSDs of inter-day were between 6.4% and 22.6%. The limits of detection (LOD, S/N = 3) were in the range of 0.003 - 0.015 ng/g except the LOD of BDE-209 was 0.15 ng/g. The results indicated that the proposed method is sensitive, accurate, fast, simple, low solvent consumption and suitable for the determination of tri- to deca-BDEs in indoor dust. PMID:23593880

Zhang, Xiaoling; Wang, Bingling; Lu, Xiaomei; Zhang, Qi; Zhang, Zhengdong

2012-12-01

19

Negative Ion Chemical Ionization Mass Spectrometry for the Analysis of 3,5,6-trichloro-2-pyridinol in Saliva of Rats Exposed to Chlorpyrifos  

SciTech Connect

Organophosphorus (OP) insecticides (e.g. chlorpyrifos) are widely used in a variety of applications, and the potential exists for significant occupational and environmental exposures. They have been associated with more occupational poisoning cases than any other class of insecticides. One of the best approaches for accurately assessing human dosimetry and determining risk from both occupational and environmental exposure is biomonitoring. Biological matrices such as blood and urine have been routinely used for biomonitoring; however, other matrices such as saliva represent a simple and readily obtainable fluid. As a result, saliva has been suggested as an alternative biological matrix for the evaluation of a broad range of biomarkers such as environmental contaminants, drugs of abuse, hormones, chemotherapeutics, heavy metals, and pesticides. Chlorpyrifos (CPF), and its major metabolite, 3,5,6-trichloro-2-pyridinol (TCP), have been quantified in urine and blood as a biomarker for exposure to OP insecticides. The purpose of this study was to develop an analytical approach for detecting and quantitating the levels of TCP in saliva obtained from rats exposed to CPF and to evaluate the potential of saliva as a non-invasive biomonitoring matrix. Adult male rats were administered CPF, and blood and saliva were humanely collected for analysis of TCP and CPF. TCP was detected and quantitated in saliva using negative ion chemical ionization mass spectrometry with selected ion monitoring. Initial results indicate that saliva may be potentially utilized as a non-invasive biomonitoring matrix to determine exposure to organophosphate insecticides.

Campbell, James A.; Timchalk, Chuck; Kousba, Ahmed A.; Wu, Hong; Valenzuela, Blandina R.; Hoppe, Eric W.

2005-05-01

20

Negative ion chemical ionization-gas chromatographic-mass spectrometric determination of residues of different pyrethroid insecticides in whole blood and serum.  

PubMed

A new rapid and sensitive analytical method using negative ion chemical ionization-gas chromatography-mass spectrometry in selective ion monitoring mode has been developed for the determination of residues of different synthetic pyrethroid insecticides, allethrin, bifenthrin, cypermethrin, cyphonothrin, cyfluthrin, lambda-cyhalothrin, deltamethrin, fenvalerate, fenpropathrin, permethrin, prallethrin, and trans-fluthrin, in whole blood. The residues of pyrethroid molecules were extracted from the whole blood using a hexane and acetone (8:2, v/v) solvent mixture without separating the serum. The method was found sensitive to detect the residues of pyrethroids up to the level 0.2 pg/mL. Experiments conducted with the whole blood samples at the fortification level 1-100 pg/mL showed 91-103% recovery, whereas blood serum samples collected after the fortification of pyrethroids in whole blood showed 36-54% recovery. Recovery experiments conducted by direct fortification of pyrethroids in blood serum samples showed 96-108%. The applications of the analytical method was tested by analyzing 73 human blood samples collected from the population exposed continuously to different pyrethroid-based formulations. None of the blood samples showed residues of pyrethroids. The results were also confirmed by the detection of the appropriate amounts in a number of these samples, which had subsequently been spiked with known quantity of pyrethroids. PMID:15538961

Ramesh, Atmakuru; Ravi, Perumal Elumalai

2004-01-01

21

Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry  

Microsoft Academic Search

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO3-(H2O)n and NO3-(H2O)n with HNO3. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N2-buffer

O. Moehler; F. Arnold

1991-01-01

22

Analysis of low erucic acid turnip rapeseed oil ( Brassica campestris ) by negative ion chemical ionization tandem mass spectrometry. A method giving information on the fatty acid composition in positions sn -2 and sn -1\\/3 of triacylglycerols  

Microsoft Academic Search

A tandem mass spectrometric method is described for the rapid analysis of fatty acid combinations in mixtures of triacylglycerols.\\u000a Triacylglycerols were introduced into a triple quadrupole mass spectrometervia a direct exposure probe and deprotonated using ammonia negative ion chemical ionization. Collisionally activated spectra\\u000a were obtained and the resulting fragments used to identify the fatty acid constituents, and the fatty acids

Heikki Kallio; Graeme Currie

1993-01-01

23

Ionization mechanisms related to negative Ion APPI, APCI, and DART  

Microsoft Academic Search

A recent report found that negative ion atmospheric pressure photoionization (Ni-APPI) and direct analysis in real time (Ni-DART)\\u000a ionize compounds by electron capture, dissociative electron capture, proton abstraction, and anion adduction. The authors\\u000a of this report suggested that the common ionization of Ni-APPI and Ni-DART demonstrated that these techniques ionize a wider\\u000a array of compounds than negative ion atmospheric pressure

Charles N. McEwen; Barbara S. Larsen

2009-01-01

24

USE OF NEGATIVE ARI IONIZATION FOR REDUCING BACTERIAL PATHOGENS AND SPORES ON STAINLESS STEEL SURFACES  

Technology Transfer Automated Retrieval System (TEKTRAN)

The use of chemicals in food plant sanitation for removing and killing microorganisms could be reduced by the use of alternative non-chemical interventions. Negative air ionization is a new technology that has shown potential to effectively reduce airborne and surface microorganisms. Current studies...

25

A positive (negative) surface ionization source concept for RIB generation  

SciTech Connect

A novel, versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed and fabricated which will have the capability of generating both positive- and negative-ion beams without mechanical changes to the source. The source utilizes a highly permeable, high-work-function Ir ionizer ({phi}{approximately} = 5.29 eV) for ionizing highly electropositive atoms/molecules; while for negative-surface ionization, the work function is lowered to {phi} {approximately} = 1.43 eV by continually feeding cesium vapor through the ionizer matrix. The use of Cs to effect low work function surfaces for negative ion beam generation has the potential of overcoming the chronic poisoning effects experienced with LaB{sub 6} while enhancing the probability for negative ion formation of atomic and molecular species with low to intermediate electron affinities. The flexibility of operation in either mode makes it especially attractive for RIB applications and, therefore, the source will be used as a complementary replacement for the high-temperature electron impact ionization sources presently in use at the HRIBF The design features and operational principles of the source will be described in this report.

Alton, G.D.; Mills, G.D.

1995-12-31

26

Chemical form effects on the surface ionization of lithium halides  

Microsoft Academic Search

The surface ionization of lithium halides, i.e. fluoride, chloride, bromide and iodide, was studied using a mass spectrometer. In the measurements of ionization using rhenium filaments, it was found that the ionization efficiencies depend on the chemical forms of the samples. To analyze the mechanism of ionization, direct ionization by dissociative ionization is introduced in the present work. The ionization

Tatsuya Suzuki; Hideki Iwabuchi; Kazuko Takahashi; Masao Nomura; Makoto Okamoto; Yasuhiko Fujii

1995-01-01

27

Identification and quantification of astaxanthin esters in shrimp (Pandalus borealis) and in a microalga (Haematococcus pluvialis) by liquid chromatography-mass spectrometry using negative ion atmospheric pressure chemical ionization.  

PubMed

Negative ion liquid chromatography-atmospheric pressure chemical ionization mass spectrometry [negative ion LC-(APCI)MS] was used for the identification of astaxanthin esters in extracts of commercial shrimp (Pandalus borealis) and dried microalga (Haematococcus pluvialis) samples. A cleanup step using a normal phase solid phase extraction (SPE) cartridge was applied prior to analysis. Recovery experiments with astaxanthin oleate as model compound proved the applicability of this step (98.5 +/- 7.6%; n = 4). The assignment of astaxanthin esters in negative ion LC-(APCI)MS was based on the detection of the molecular ion (M*-) and the formation of characteristic fragment ions, resulting from the loss of one or two fatty acids. Quantification of individual astaxanthin esters was performed using an astaxanthin calibration curve, which was found to be linear over the required range (1-51 micromol/L; r2 = 0.9996). Detection limits, based on the intensity of M*-, a signal-to-noise ratio of 3:1, and an injection volume of 20 microL, were estimated to be 0.05 microg/mL (free astaxanthin), 0.28 microg/mL (astaxanthin-C16:0), and 0.78 microg/mL (astaxanthin-C16:0/C16:0), respectively. This LC-(APCI)MS method allows for the first time the characterization of native astaxanthin esters in P. borealis and H. pluvialis without using time-consuming isolation steps with subsequent gas chromatographic analyses of fatty acid methyl esters. The results suggest that the pattern of astaxanthin-bound polyunsaturated fatty acids of P. borealis does not reflect the respective fatty acid pattern found in triacylglycerides. Application of the presented LC-(APCI)MS technique in common astaxanthin ester analysis will forestall erroneous xanthophyll ester assignment in natural sources. PMID:15186109

Breithaupt, Dietmar E

2004-06-16

28

Measurement of HONO, HNCO, and Other Inorganic Acids by Negative-ion Proton-Transfer Chemical-Ionization Mass Spectrometry (NI-PT-CIMS):Application to Biomass Burning Emissions.  

SciTech Connect

A negative-ion proton transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO) nitric (HNO3), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO3 and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4 seconds, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO3•NO3- clusters within the CIMS, and NO2-water production on inlet surfaces, and were quite minor (>_1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume). The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, and suggest both as products of biomass burning.

Roberts, James M.; Veres, Patrick; Warneke, Carsten; Neuman, Andrew; Washenfelder, Rebecca; Brown, Steven; Baasandroj, Munkhbayar; Burkholder, James; Burling, Ian; Johnson, Timothy J.; Yokelson, Robert L.; de Gouw, Joost A.

2010-07-23

29

Production of negative osmium ions by laser desorption and ionization  

NASA Astrophysics Data System (ADS)

The interest to produce negative osmium ions is manifold in the realm of high-accuracy ion trap experiments: high-resolution nearly Doppler-free laser spectroscopy, antihydrogen formation in its ground state, and contributions to neutrino mass spectrometry. Production of these ions is generally accomplished by sputtering an Os sample with Cs+ ions at tens of keV. Though this is a well-established method commonly used at accelerators, these kind of sources are quite demanding and tricky to operate. Therefore, the development of a more straightforward and cost effective production scheme will be of benefit for ion trap and other experiments. Such a scheme makes use of desorption and ionization with pulsed lasers and identification of the ions by time-of-flight mass spectrometry. First investigations of negative osmium ion production using a pulsed laser for desorption and ionization and a commercial matrix-assisted laser desorption/ionization time-of-flight system for identification has demonstrated the suitability of this technique. More than 103 negative osmium ions per shot were registered after bombarding pure osmium powder with a 5 ns pulse width Nd:yttrium aluminum garnet laser. The limitation in the ion number was imposed by the detection limit of the microchannel plate detector.

Rodríguez, D.; Sonnenschein, V.; Blaum, K.; Block, M.; Kluge, H.-J.; Lallena, A. M.; Raeder, S.; Wendt, K.

2010-01-01

30

Simultaneous detection of stable isotope-labeled and unlabeled L-tryptophan and of its main metabolites, L-kynurenine, serotonin and quinolinic acid, by gas chromatography/negative ion chemical ionization mass spectrometry.  

PubMed

A method for the detection of unlabeled and (15)N2 -labeled L-tryptophan (L-Trp), L-kynurenine (L-Kyn), serotonin (5-HT) and quinolinic acid (QA) in human and rat plasma by GC/MS is described. Labeled and unlabeled versions of these four products were analyzed as their acyl substitution derivatives using pentafluoropropionic anhydride and 2,2,3,3,3-pentafluoro-1-propanol. Products were then separated by GC and analyzed by selected ion monitoring using negative ion chemical ionization mass spectrometry. L-[(13)C11, (15)N2]-Trp, methyl-serotonin and 3,5-pyridinedicarboxylic acid were used as internal standards for this method. The coefficients of variation for inter-assay repeatability were found to be approximately 5.2% for L-Trp and (15)N2-Trp, 17.1% for L-Kyn, 16.9% for 5-HT and 5.8% for QA (n?=?2). We used this method to determine isotope enrichments in plasma L-Trp over the course of a continuous, intravenous infusion of L-[(15) N2 ]Trp in pregnant rat in the fasting state. Plasma (15)N2-Trp enrichment reached a plateau at 120?min. The free Trp appearance rate (Ra) into plasma was 49.5?±?3.35?µmol/kg/h. The GC/MS method was applied to determine the enrichment of (15)N-labeled L-Trp, L-Kyn, 5-HT and QA concurrently with the concentration of non-labeled L-Trp, L-Kyn, 5-HT and QA in plasma. This method may help improve our understanding on L-Trp metabolism in vivo in animals and humans and potentially reveal the relative contribution of the four pathways of L-Trp metabolism. PMID:24677305

Sano, Mitsue; Ferchaud-Roucher, Véronique; Nael, Charlotte; Aguesse, Audrey; Poupeau, Guillaume; Castellano, Blandine; Darmaun, Dominique

2014-02-01

31

Chemical protection against ionizing radiation. Final report  

SciTech Connect

The scientific literature on radiation-protective drugs is reviewed. Emphasis is placed on the mechanisms involved in determining the sensitivity of biological material to ionizing radiation and mechanisms of chemical radioprotection. In Section I, the types of radiation are described and the effects of ionizing radiation on biological systems are reviewed. The effects of ionizing radiation are briefly contrasted with the effects of non-ionizing radiation. Section II reviews the contributions of various natural factors which influence the inherent radiosensitivity of biological systems. Inlcuded in the list of these factors are water, oxygen, thiols, vitamins and antioxidants. Brief attention is given to the model describing competition between oxygen and natural radioprotective substances (principally, thiols) in determining the net cellular radiosensitivity. Several theories of the mechanism(s) of action of radioprotective drugs are described in Section III. These mechanisms include the production of hypoxia, detoxication of radiochemical reactive species, stabilization of the radiobiological target and the enhancement of damage repair processes. Section IV describes the current strategies for the treatment of radiation injury. Likely areas in which fruitful research might be performed are described in Section V. 495 references.

Livesey, J.C.; Reed, D.J.; Adamson, L.F.

1984-08-01

32

Chemical form effects on the surface ionization of lithium halides  

NASA Astrophysics Data System (ADS)

The surface ionization of lithium halides, i.e. fluoride, chloride, bromide and iodide, was studied using a mass spectrometer. In the measurements of ionization using rhenium filaments, it was found that the ionization efficiencies depend on the chemical forms of the samples. To analyze the mechanism of ionization, direct ionization by dissociative ionization is introduced in the present work. The ionization parameter [var epsilon] has been experimentally shown to be [var epsilon] = [phi]DI-W, where [phi]DI is the dissociative ionization energy, and W is the work function. In conclusion, a Saha-Langmuir-type equation is applicable to the surface ionization of lithium halides using the dissociative ionization energy term instead of the ionization potential of atoms.

Suzuki, Tatsuya; Iwabuchi, Hideki; Takahashi, Kazuko; Nomura, Masao; Okamoto, Makoto; Fujii, Yasuhiko

1995-07-01

33

Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometry of Carotenoids  

PubMed Central

Carotenoids are natural pigments synthesized by plants and photosynthetic microorganisms, some of which, like ?-carotene, are precursors of vitamin A, and others such as lutein and lycopene might function in the prevention of age-related macular degeneration and prostate cancer, respectively. Mass spectrometry provides high sensitivity and selectivity for the identification and quantitative analysis of carotenoids in biological samples, and previous studies have described how atmospheric pressure chemical ionization (APCI) offers distinct advantages over electrospray and fast atom bombardment for the analysis of specific carotenoids. Since APCI product ion tandem mass spectra have been reported for only a few carotenoids, a detailed investigation of twelve carotenes and xanthophylls was carried out using both positive ion and negative ion APCI tandem mass spectrometry with collision-induced dissociation. Using protonated molecules as precursor ions in positive ion mode and radical anions in negative ion mode, characteristic fragment ions were identified that may be used to distinguish between carotenoids. PMID:22408388

van Breemen, Richard B.; Dong, Linlin; Pajkovic, Natasa D.

2011-01-01

34

ELECTRON-CAPTURE NEGATIVE IONIZATION CALIBRANTS FOR MAGNETIC SECTOR MASS SPECTROMETERS  

EPA Science Inventory

Fomblin poly(perfluoropropylene oxide). FK (perfluorokerosene) and FC-43 (perflurotributylamine) are investigated as mass calibrants in electron-capture negative ionization mass spectrometry on a magnetic sector hybrid mass spectrometer. This work provides exact negative ion mass...

35

Alternative Filament Loading Solution for Accurate Analysis of Boron Isotopes by Negative Thermal Ionization Mass Spectrometry  

Microsoft Academic Search

The negative thermal ionization mass spectrometry technique has become the major tool for investigating boron isotopes in the environment. The high sensitivity of BO2- ionization enables measurements of ng levels of boron. However, B isotope measurement by this technique suffers from two fundamental problems (1) fractionation induced by selective ionization of B isotopes in the mass spectrometer; and (2) CNO-

G. S. Dwyer; A. Vengosh

2008-01-01

36

Choosing between atmospheric pressure chemical ionization and electrospray ionization interfaces for the HPLC/MS analysis of pesticides  

USGS Publications Warehouse

An evaluation of over 75 pesticides by high-performance liquid chromatography/mass spectrometry (HPLC/MS) clearly shows that different classes of pesticides are more sensitive using either atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI). For example, neutral and basic pesticides (phenylureas, triazines) are more sensitive using APCI (especially positive ion). While cationic and anionic herbicides (bipyridylium ions, sulfonic acids) are more sensitive using ESI (especially negative ion). These data are expressed graphically in a figure called an ionization-continuum diagram, which shows that protonation in the gas phase (proton affinity) and polarity in solution, expressed as proton addition or subtraction (pKa), is useful in selecting APCI or ESI. Furthermore, sodium adduct formation commonly occurs using positive ion ESI but not using positive ion APCI, which reflects the different mechanisms of ionization and strengthens the usefulness of the ionization-continuum diagram. The data also show that the concept of "wrong-way around" ESI (the sensitivity of acidic pesticides in an acidic mobile phase) is a useful modification of simple pKa theory for mobile-phase selection. Finally, this finding is used to enhance the chromatographic separation of oxanilic and sulfonic acid herbicides while maintaining good sensitivity in LC/MS using ESI negative.

Thurman, E.M.; Ferrer, I.; Barcelo, D.

2001-01-01

37

A high-efficiency positive (negative) surface ionization source for RIB generation  

SciTech Connect

A versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed and fabricated which will have the capability of generating both positive- and negative-ion beams without mechanical changes to the source. The source utilizes a highly permeable, high-work-function Ir ionizer ({phi} {congruent} 5. 229 eV) for ionizing highly electropositive atoms/molecules; while for negative-surface ionization, the work function is lowered to {phi} {congruent} 1.43 eV by continually feeding cesium vapor through the ionizer matrix. The use of this technique for negative ion beam generation has the potential of overcoming the chronic poisoning effects experienced with LaB{sub 6} while enhancing considerably the efficiency for negative surface ionization of atomic and molecules with intermediate electron affinities. The flexibility of operation in either mode makes it especially attractive for RIB applications and, therefore, the source will be used as a complementary replacement for the high-temperature electron impact ionization sources presently in use at the HRIBF. The design features and operational principles of the source will be described in this report.

Alton, G.D.; Mills, G.D.

1995-12-31

38

Plasma-Assisted Reaction Chemical Ionization for Elemental Mass Spectrometry of Organohalogens  

NASA Astrophysics Data System (ADS)

We present plasma-assisted reaction chemical ionization (PARCI) for elemental analysis of halogens in organic compounds. Organohalogens are broken down to simple halogen-containing molecules (e.g., HBr) in a helium microwave-induced plasma followed by negative mode chemical ionization (CI) in the afterglow region. The reagent ions for CI originate from penning ionization of gases (e.g., N2) introduced into the afterglow region. The performance of PARCI-mass spectrometry (MS) is evaluated using flow injection analyses of organobromines, demonstrating 5-8 times better sensitivities compared with inductively coupled plasma MS. We show that compound-dependent sensitivities in PARCI-MS mainly arise from sample introduction biases.

Wang, Haopeng; Lin, Ninghang; Kahen, Kaveh; Badiei, Hamid; Jorabchi, Kaveh

2014-04-01

39

Ammonia chemical ionization mass spectrometry of intact diacyl phosphatidylcholine  

Microsoft Academic Search

Mass spectra have been obtained on molecular spe- cies of intact diacyl phosphatidylcholine by means of ammonia gas-induced chemical ionization. MH+ ions were observed with all species, and other prominent ions in the spectra identified the fatty acid composition. Spectra of phosphatidylcholine con- taining deuterated methyl groups and spectra obtained using ( ''Nlammonia have allowed identification of fragments con- taining

C. G. Crawford; R. D. Plattner

40

UPTAKE OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS  

EPA Science Inventory

Uptake of organic acids by fish, and their toxicity, generally decrease with increasing pH above the pK, presumably due to neutral forms of such chemicals being more readily adsorbed than their ionized forms. However, uptake usually exceeds that expected based just on the concent...

41

Quantitative aspects of and ionization mechanisms in positive-ion atmospheric pressure chemical ionization mass spectrometry.  

PubMed

The behavior in atmospheric pressure chemical ionization of selected model polycyclic aromatic compounds, pyrene, dibenzothiophene, carbazole, and fluorenone, was studied in the solvents acetonitrile, methanol, and toluene. Relative ionization efficiency and sensitivity were highest in toluene and lowest in methanol, a mixture of molecular ions and protonated molecules was observed in most instances, and interferences between analytes were detected at higher concentrations. Such interferences were assumed to be caused by a competition among analyte molecules for a limited number of reagent ions in the plasma. The presence of both molecular ions and protonated analyte molecules can be attributed to charge-transfer from solvent radical cations and proton transfer from protonated solvent molecules, respectively. The order of ionization efficiency could be explained by incorporating the effect of solvation in the ionization reactions. Thermodynamic data, both experimental and calculated theoretically, are presented to support the proposed ionization mechanisms. The analytical implications of the results are that using acetonitrile (compared with methanol) as solvent will provide better sensitivity with fewer interferences (at low concentrations), except for analytes having high gas-phase basicities. PMID:18845448

Herrera, Lisandra Cubero; Grossert, J Stuart; Ramaley, Louis

2008-12-01

42

Negative ion sources equipped with continuous annular and spherical geometry surface ionizers  

SciTech Connect

Axial geometry negative ion sources have been designed, developed, and evaluated for use in conjunction with tandem accelerator applications. These sources utilize continuous surface solid tungsten ionizers in either annular or spherical geometries to effect ionization of cesium vapor, which in turn is used to sputter a negatively biased probe containing the material of interest. The annular ionizer geometry source has been incorporated as an ''on-line'' source for routine operation of the Holifield Heavy Ion Research Facility (HHIRF) tandem accelerator. Both test stand and tandem accelerator operational experience indicate that such sources are reliable, long lived, stably operating and prolific producers of a wide spectrum of negative ions. To date these sources have been used to produce more than 18 negative ion species including Ag/sup -/, Au/sup -/, B/sup -/, CaH/sub 3//sup -/, Cl/sup -/, CrH/sub 2//sup -/, Cu/sup -/, Lu/sup -/, MgH/sub 3//sup -/, Mo/sup -/, Ni/sup -/, O/sup -/, S/sup -/, Si/sup -/, Sn/sup -/, TiH/sub 3//sup -/, Tm/sup -/, and Yb/sup -/. Details of the mechanical design features and computational techniques utilized in arriving at the final electrode configuration are presented in the text. Examples of data pertinent to source operation, the dependence of negative ion yields on certain source operational parameters and of intensities typical of a particular negative ion source are also given. 12 refs., 10 figs.

Alton, G.D.; Mills, G.D.

1985-01-01

43

Terahertz Spectroscopy of Water Vapors, Chemical Vapors and Ionized Air  

NASA Astrophysics Data System (ADS)

In the past, a few research groups have demonstrated that terahertz spectroscopy could be a useful tool for the identification of chemicals. However most of those demonstrations have been done with solid-phase or liquid-phase chemicals. There are little demonstrations for the detection and identification of chemicals in the gas-phase, as it is very difficult in part due to the presence of water-absorption lines in the terahertz frequency range. As the water absorption lines predominate in the 0.1 - 2THz spectral range, and can interfere with already weak terahertz signatures generated by chemical vapors, it is often very hard to obtain meaningful terahertz spectrum of chemical vapor. Regardless we recently have been able to obtain some terahertz spectra of chemical vapors and ionized air produced by several different ionization sources, including corona discharge and nuclear isotopes. Throughout data analysis we learned that water molecules, nitrogen and oxygen molecules play very important roles in these terahertz spectra. In this presentation we will discuss our experiments and the roles of these molecules.

Graber, Benjamin; Tao, Rongjia; Wu, Dong Ho

2013-03-01

44

Controlled Trial of Naturalistic Dawn Simulation and Negative Air Ionization for Seasonal Affective Disorder  

Microsoft Academic Search

Objective: This trial assessed two novel nonpharmaceutical treatments for winter depression—naturalistic dawn simulation and high-density negative air ionization— delivered during the final hours of sleep. Method: The patients were 99 adults (77 women and 22 men) with the winter sea- sonal pattern of major depressive disor- der (94 cases) and bipolar II disorder (five

Michael Terman; J. S. Terman

2006-01-01

45

Multiphoton ionization of negative ions in the presence of a dc FIELD. Application to Li -  

NASA Astrophysics Data System (ADS)

We present results from the application of a nonperturbative, many-electron, many-photon (MEMP) theory of ionization to Li -, in the presence and absence of an external dc field. In conjunction with published theoretical and experimental data, our calculations suggest that although initial-state electron correlation influences the absolute values of the multiphoton ionization cross-sections, much of the essential physics of negative ions in strong external ac and dc fields is caused by final-state effects (atomic structure of the core plus field-perturbed free electron).

Nicolaides, C. A.; Mercouris, Th.

1989-06-01

46

Upper-Room Ultraviolet Light and Negative Air Ionization to Prevent Tuberculosis Transmission  

Microsoft Academic Search

BackgroundInstitutional tuberculosis (TB) transmission is an important public health problem highlighted by the HIV\\/AIDS pandemic and the emergence of multidrug- and extensively drug-resistant TB. Effective TB infection control measures are urgently needed. We evaluated the efficacy of upper-room ultraviolet (UV) lights and negative air ionization for preventing airborne TB transmission using a guinea pig air-sampling model to measure the TB

A. Roderick Escombe; David A. J Moore; Robert H Gilman; Marcos Navincopa; Eduardo Ticona; Bailey Mitchell; Catherine Noakes; Carlos Martínez; Patricia Sheen; Rocio Ramirez; Willi Quino; Armando Gonzalez; Jon S Friedland; Carlton A Evans

2009-01-01

47

Positive and Negative Self-Surface Ionization of Tungsten and Rhenium  

Microsoft Academic Search

The self-surface ionization of tungsten and rhenium has been investigated with a specially designed mass spectrometer. It has been found that both positive and negative singly charged atomic ions sublime from these metal surfaces in the 1900°—2600°K temperature range. The assumption that these processes can be described by a generalized Saha—Langmuir equation has been shown to be valid. The energies

Milton D. Scheer; Joseph Fine

1967-01-01

48

A new concept positive (negative) surface ionization source for RIB applications  

SciTech Connect

A versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed. fabricated, and tests completed which can operate in either positive- or negative-ion beam generation modes without mechanical changes to the source. The highly permeable, composite Ir/C has an intrinsic work function of 0 = 5.29 eV and can be used directly for the generation of positive-ion beams of highly electropositive elements. For negative-surface ionization, the work function is lowered by dynamic flow of a highly electropositive adsorbate such as Cs through the ionizer matrix. The results of initial testing indicate that the source is reliable, stable and easy to operate, with efficiencies for Cs{sup +} estimated to exceed 60% and as high as {approximately}50% for F{sup -} generation. The design features, operational principles, and initial performance of the source for generating Cs{sup +} and F{sup -}, when operated with Cs, are discussed in this article.

Alton, G.D. [Oak Ridge National Lab., TN (United States); Welton, R.F. [Oak Ridge Institute of Science and Engineering, TN (United States); Cui, B. [China Institute of Atomic Energy, Beijing (China)] [and others

1996-12-31

49

Application of Ni-63 photo and corona discharge ionization for the analysis of chemical warfare agents and toxic wastes  

NASA Technical Reports Server (NTRS)

Over the past decade, advances in instrumental design and refinements in the understanding of ion molecule reactions at atmospheric pressure enabled the application of Ion Mobility Spectrometry (IMS) as a simple inexpensive and sensitive analytical method for the detection of organic trace compounds. Positive and negative gas-phase ions for ion mobility spectrometry have been produced by a variety of methods, including photo-ionization, laser multi photon ionization, surface ionization, corona discharge ionization. The most common ion source used in ion mobility spectrometry is a radioactive Ni-63 foil which is favored due to simplicity, stability, convenience, and high selectivity. If reactant ions like (H2O(n)H)(+) or (H2O(n)O2)(-) dominate in the reaction region, nearly all kinds of compounds with a given proton or electron affinity; are ionized. However, the radioactivity of the Ni-63 foil is one disadvantage of this ion source that stimulates the development and application of other ionization techniques. In this paper, we report analyses of old chemical warfare agents and toxic wastes using Bruker RAID ion mobility spectrometers. Due to the modular construction of the measuring cell, the spectrometers can be equipped with different ion sources. The combined use of Ni-63, photo- and corona discharge ionization allows the identification of different classes of chemical compounds and yields in most cases comparable results.

Stach, J.; Adler, J.; Brodacki, M.; Doring, H.-R.

1995-01-01

50

Methods for estimating the bioconcentration factor of ionizable organic chemicals.  

PubMed

The bioaccumulation potential is an important criterion in risk assessment of chemicals. Several regressions between bioconcentration factor (BCF) in fish and octanol-water partition coefficient (K(OW)) have been developed for neutral organic compounds, but very few approaches address the BCF of ionizable compounds. A database with BCFs of 73 acids and 65 bases was collected from the literature. The BCF estimation method recommended by the Technical Guidance Document (TGD) for chemical risk assessment in the European Union was tested for ionizing substances using log K(OW) (corrected for the neutral species, log[ f(n) x K(OW)]) and log D (sum of log K(OW) of neutral and ionic molecule, apparent log K(OW)) as predictors. In addition, the method of Meylan et al. (Environ Toxicol Chem 1999; 18:664-672) for ionizable compounds and a dynamic cell model based on the Fick- Nernst-Planck equation were tested. Moreover, our own regressions for the BCF were established from log K(OW) and pK(a). The bioaccumulation of lipophilic compounds depends mainly on their lipophilicity, and the best predictor is log D. Dissociation, the pH-dependent ion trap, and electrical attraction of cations impact the BCF. Several methods showed acceptable results. The TGD regressions gave good predictions when log( f(n) x K(OW)) or log D were used as a predictor instead of log K(OW). The new regressions to log K(OW) and pK(a) performed similarly, with mean errors of approximately 0.4. The method of Meylan et al. did not perform as well. The cell model showed weak results for acids but was among the best methods for bases. PMID:19245273

Fu, Wenjing; Franco, Antonio; Trapp, Stefan

2009-07-01

51

A Negative-Surface Ionization for Generation of Halogen Radioactive Ion Beams  

SciTech Connect

A simple and efficient negative surface ionization source has been designed, fabricated and initially tested for on-line generation of radioactive ion beams of the halogens (Cl, Br, I, and At) for use in the nuclear-structure and nuclear-astrophysics research programs at the Holifield Radioactive Ion Beam Facility. The source utilizes a solid, spherical geometry LaB{sub 6} surface ionizer for forming highly electronegative atoms and molecules. Despite its widely publicized propensity for being easily poisoned, no evidences of this effect were experienced during testing of the source. Nominal efficiencies of 15% for Br{sup {minus}} beam generation were obtained during off-line evaluation of the source with AlBr3 feed material when account is taken of the fractional dissociation of the molecule. Principles of operation, design features, operational parameter data, initial performance results, and beam quality data (emittance) are presented in this article.

Zaim, H.

2001-04-16

52

Effect of sample compositions on chemical analysis using matrix-assisted laser desorption ionization mass spectrometry  

Microsoft Academic Search

Matrix-assisted laser desorption ionization (MALDI) is an effective ionization technique for mass spectrometry. It take advantages of some unique properties of certain organic chemicals to provide entrapment, isolation, vaporization, and ionization of the analyte of interest. While the main application of the MALDI technique is currently in the area of biological molecule analysis, it is possible to use this technique

David Schriemer; Yuqin Dai; Liang Li

1996-01-01

53

Alternative Filament Loading Solution for Accurate Analysis of Boron Isotopes by Negative Thermal Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The negative thermal ionization mass spectrometry technique has become the major tool for investigating boron isotopes in the environment. The high sensitivity of BO2- ionization enables measurements of ng levels of boron. However, B isotope measurement by this technique suffers from two fundamental problems (1) fractionation induced by selective ionization of B isotopes in the mass spectrometer; and (2) CNO- interference on mass 42 that is often present in some load solutions (such as B-free seawater processed through ion-exchange resin). Here we report a potentially improved methodology using an alternative filament loading solution with a recently-installed Thermo Scientific TRITON thermal ionization mass spectrometer. Our initial results suggest that this solution -- prepared by combining high-purity single- element standard solutions of Ca, Mg, Na, and K in proportions similar to those in seawater in a 5% HCl matrix -- may offer significant improvement over some other commonly used load solutions. Total loading blank is around 15pg as determined by isotope dilution (NIST952). Replicate analyses of NIST SRM951 and modern seawater thus far have yielded 11B/10B ratios of 4.0057 (±0.0008, n=14) and 4.1645 (±0.0017, n=7; ?11B=39.6 permil), respectively. Replicate analyses of samples and SRM951 yield an average standard deviation (1 ?) of approximately 0.001 (0.25 permil). Fractionation during analysis (60-90 minutes) has thus far typically been less than 0.002 (0.5 permil). The load solution delivers ionization efficiency similar to directly-loaded seawater and has negligible signal at mass 26 (CN-), a proxy for the common interfering molecular ion (CNO-) on mass 42. Standards and samples loaded with the solution behave fairly predictably during filament heating and analysis, thus allowing for the possibility of fully automated data collection.

Dwyer, G. S.; Vengosh, A.

2008-12-01

54

The Effect of Salts on Electrospray Ionization of Amino Acids in the Negative Mode  

NASA Technical Reports Server (NTRS)

The continued search for organics on Mars will require the development of simplified procedures for handling and processing of soil or rock core samples prior to analysis by onboard instrumentation. Extraction of certain organic molecules such as amino acids from rock and soil samples using a liquid solvent (H2O) has been shown to be more efficient (by approximately an order of magnitude) than heat extraction methods. As such, liquid extraction (using H2O) of amino acid molecules from rock cores or regolith material is a prime candidate for the required processing. In this scenario, electrospray ionization (ESI) of the liquid extract would be a natural choice for ionization of the analyte prior to interrogation by one of a variety of potential analytical separation techniques (mass spectroscopy, ion mobility spectroscopy, etc.). Aside from the obvious compatibility of ESI and liquid samples, ESI offers simplicity and a soft ionization capability. In order to demonstrate that liquid extraction and ESI can work as part of an in situ instrument on Mars, we must better understand and quantify the effect salts have on the ESI process. In the current work, we have endeavored to investigate the feasibility and limitations of negative mode ESI of Martian surface samples in the context of sample salt content using ion mobility spectroscopy (IMS).

Kim, H. I.; Johnson, P. V.; Beegle, L. W.; Kanik, I.

2004-01-01

55

Ammonia chemical ionization tandem mass spectrometry in structural determination of alkaloids.  

E-print Network

Ammonia chemical ionization tandem mass spectrometry in structural determination of alkaloids. II 7 June 2001 Chemical ionization tandem mass spectrometry (CI-MS/MS) of alkaloids with ammonia alkaloids in extracts from six pseudomyrmecine ants of the genus Tetraponera. The MS/MS techniques along

56

Quantitative analysis of acyl-lysophosphatidic acid in plasma using negative ionization tandem mass spectrometry.  

PubMed

Analysis of acyl-lysophosphatidic acids (LPAs) has clinical importance as a potential biomarker for ovarian and other gynecological cancers or obesity from the point of view of prevention. Here we report a simple sample preparation and analytical method with high sensitivity and specificity for the early detection of gynecological cancers to improve the overall outcome of this disease. We established a novel quantification method for acyl-LPAs in plasma by electrospray negative ionization tandem mass spectrometry (MS-MS) using multiple reaction monitoring mode without conventional TLC step. Protein-bound lipids, acyl-LPAs in plasma were extracted with methanol/chloroform (2:1) containing LPA C(14:0) as internal standard under acidic conditions. Following back-extraction with chloroform and water, the centrifuged lower phase was evaporated and reconstituted in methanol and then analyzed. Using ESI-MS-MS with negative ionization MRM mode, all the species of LPAs were completely separated from plasma matrix without severe interference. For MRM mode, Q1 ions selected were m/z 409, 433, 435, 437 and 457 which corresponds to molecular mass [M-H](-) of C(16:0), C(18:2), C(18:1), C(18:0) and C(20:4) LPA, respectively. Q2 ions selected for MRM was m/z 79, phosphoryl product. Using MS-MS with MRM mode, all the species of LPAs were completely separated from plasma matrix without severe interference. This method allowed simultaneous detection and quantification of different species of LPAs in plasma over a linear dynamic range of 0.01-25 micromol/l. The method detection limit was 0.3 pmol/ml with correlation coefficient of 0.9983 in most LPAs analyzed. When applied to plasma from normal and gynecological cancer patients, this new method differentiated two different groups by way of total LPA level. PMID:12668074

Yoon, Hye-Ran; Kim, Hohyun; Cho, Sam-Hyun

2003-05-01

57

Specific Interaction Between Negative Atmospheric Ions and Organic Compounds in Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O{2/-}, HCO{3/-}, COO-(COOH), NO{2/-}, NO{3/-}, and NO{3/-}(HNO3) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion.

Sekimoto, Kanako; Sakai, Mami; Takayama, Mitsuo

2012-06-01

58

Sensitive and comprehensive detection of chemical warfare agents in air by atmospheric pressure chemical ionization ion trap tandem mass spectrometry with counterflow introduction.  

PubMed

A highly sensitive and specific real-time field-deployable detection technology, based on counterflow air introduction atmospheric pressure chemical ionization, has been developed for a wide range of chemical warfare agents (CWAs) comprising gaseous (two blood agents, three choking agents), volatile (six nerve gases and one precursor agent, five blister agents), and nonvolatile (three lachrymators, three vomiting agents) agents in air. The approach can afford effective chemical ionization, in both positive and negative ion modes, for ion trap multiple-stage mass spectrometry (MS(n)). The volatile and nonvolatile CWAs tested provided characteristic ions, which were fragmented into MS(3) product ions in positive and negative ion modes. Portions of the fragment ions were assigned by laboratory hybrid mass spectrometry (MS) composed of linear ion trap and high-resolution mass spectrometers. Gaseous agents were detected by MS or MS(2) in negative ion mode. The limits of detection for a 1 s measurement were typically at or below the microgram per cubic meter level except for chloropicrin (submilligram per cubic meter). Matrix effects by gasoline vapor resulted in minimal false-positive signals for all the CWAs and some signal suppression in the case of mustard gas. The moisture level did influence the measurement of the CWAs. PMID:24678766

Seto, Yasuo; Sekiguchi, Hiroshi; Maruko, Hisashi; Yamashiro, Shigeharu; Sano, Yasuhiro; Takayama, Yasuo; Sekioka, Ryoji; Yamaguchi, Shintaro; Kishi, Shintaro; Satoh, Takafumi; Sekiguchi, Hiroyuki; Iura, Kazumitsu; Nagashima, Hisayuki; Nagoya, Tomoki; Tsuge, Kouichiro; Ohsawa, Isaac; Okumura, Akihiko; Takada, Yasuaki; Ezawa, Naoya; Watanabe, Susumu; Hashimoto, Hiroaki

2014-05-01

59

A study of the tropospheric oxidation of volatile organic compounds using chemical ionization mass spectrometry  

E-print Network

The mechanisms and kinetics of reactions important to the troposphere have been investigated using a high pressure, turbulent, discharge-flow technique coupled to a chemical ionization mass spectrometer. The ability to ...

Broekhuizen, Keith Edward, 1974-

2002-01-01

60

Chemical ionization mass spectrometry of trimethylsilylated carbohydrates and organic acids retained in uremic serum.  

PubMed

After appropriate sample pretreatment and derivatization, uremic serum was investigated by combined high resolution gas chromatography and mass spectrometry, using both electron impact and chemical ionization methods. Electron impact and chemical ionization spectra of a number of identified (trimethylsilylated) carbohydrates and organic acids are compared. The utilization of chemical ionization mass spectrometry, with isobutane as the reagent gas, is discussed in detail. The influence of the reagent gas pressure on the total ion current and on the spectral appearance was studied. The identification of compounds, based on electron impact mass spectral data, was confirmed and often aided appreciably by using this technique. The chemical ionization spectra of trimethylsilyated alditols and aldonic acids, as well as of other organic acids showed protonated molecular ions, whereas aldoses did not. Differences with electron impact spectra are found mainly in the high mass region. The loss of one or more trimethylsilanol groups becomes the predominating fragmentation route at higher reagent gas pressures. PMID:534687

Schoots, A C; Leclercq, P A

1979-11-01

61

Insight into acid-base nucleation experiments by comparison of the chemical composition of positive, negative, and neutral clusters.  

PubMed

We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid-base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster-cluster collision. PMID:25406110

Bianchi, Federico; Praplan, Arnaud P; Sarnela, Nina; Dommen, Josef; Kürten, Andreas; Ortega, Ismael K; Schobesberger, Siegfried; Junninen, Heikki; Simon, Mario; Tröstl, Jasmin; Jokinen, Tuija; Sipilä, Mikko; Adamov, Alexey; Amorim, Antonio; Almeida, Joao; Breitenlechner, Martin; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Kangasluoma, Juha; Keskinen, Helmi; Kim, Jaeseok; Kirkby, Jasper; Laaksonen, Ari; Lawler, Michael J; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Tomé, António; Virtanen, Annele; Viisanen, Yrjö; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M; Ye, Penglin; Curtius, Joachim; Kulmala, Markku; Worsnop, Douglas R; Donahue, Neil M; Baltensperger, Urs

2014-12-01

62

Cooperative biological effects between ionizing radiation and other physical and chemical agents  

Microsoft Academic Search

Exposure to ionizing radiation (IR), at environmentally and therapeutically relevant doses or as a result of diagnostics or accidents, causes cyto- and genotoxic damage. However, exposure to IR alone is a rare event as it occurs in spatial and temporal combination with several physico-chemical agents. Some of these are of known noxiousness, as is the case with chemical compounds at

Lorenzo Manti; Annalisa D’Arco

2010-01-01

63

Mass spectrometric behavior of anabolic androgenic steroids using gas chromatography coupled to atmospheric pressure chemical ionization source. Part I: ionization.  

PubMed

The detection of anabolic androgenic steroids (AAS) is one of the most important topics in doping control analysis. Gas chromatography coupled to (tandem) mass spectrometry (GC-MS(/MS)) with electron ionization and liquid chromatography coupled to tandem mass spectrometry have been traditionally applied for this purpose. However, both approaches still have important limitations, and, therefore, detection of all AAS is currently afforded by the combination of these strategies. Alternative ionization techniques can minimize these drawbacks and help in the implementation of a single method for the detection of AAS. In the present work, a new atmospheric pressure chemical ionization (APCI) source commercialized for gas chromatography coupled to a quadrupole time-of-flight analyzer has been tested to evaluate the ionization of 60 model AAS. Underivatized and trimethylsylil (TMS)-derivatized compounds have been investigated. The use of GC-APCI-MS allowed for the ionization of all AAS assayed irrespective of their structure. The presence of water in the source as modifier promoted the formation of protonated molecules ([M+H](+)), becoming the base peak of the spectrum for the majority of studied compounds. Under these conditions, [M+H](+), [M+H-H2O](+) and [M+H-2·H2O](+) for underivatized AAS and [M+H](+), [M+H-TMSOH](+) and [M+H-2·TMSOH](+) for TMS-derivatized AAS were observed as main ions in the spectra. The formed ions preserve the intact steroid skeleton, and, therefore, they might be used as specific precursors in MS/MS-based methods. Additionally, a relationship between the relative abundance of these ions and the AAS structure has been established. This relationship might be useful in the structural elucidation of unknown metabolites. PMID:24913403

Raro, M; Portolés, T; Sancho, J V; Pitarch, E; Hernández, F; Marcos, J; Ventura, R; Gómez, C; Segura, J; Pozo, O J

2014-06-01

64

Approaching chemical accuracy using full configuration-interaction quantum Monte Carlo: A study of ionization potentials  

NASA Astrophysics Data System (ADS)

A new quantum Monte Carlo (QMC) method is used to calculate exact, full configuration-interaction (FCI) energies of the neutral and cationic elements from Li to Mg, in a family of commonly used basis sets. Annihilation processes between positive and negative walkers enable the exact N-electron wave function to emerge as a linear superposition of the (factorially large) space of Slater determinants, with individual determinants being stochastically sampled. As a result, extremely large spaces (exceeding 1015 determinants) become accessible for FCI calculations. No fixed-node approximation is necessary, and the only remaining source of error is the one-electron basis set, which can be systematically reduced by enlargement of the basis set. We have investigated the family of aug-cc-pVXZ Dunning basis sets up to X =5. The resulting ionization potentials are—with one exception (Na)—consistently accurate to within chemical accuracy. The anomalous case of Na suggests that its basis set may be improvable. Extrapolation schemes are examined as a way of further improving the values obtained, and although an improvement is seen in the mean-absolute error, the results of extrapolation are not uniformly better than the largest basis set calculations reported. More generally, these results demonstrate the utility of the QMC method to provide FCI energies for realistic systems and basis sets.

Booth, George H.; Alavi, Ali

2010-05-01

65

High-Resolution Desorption Electrospray Ionization Mass Spectrometry for Chemical Characterization of Organic Aerosols  

SciTech Connect

Characterization of the chemical composition and chemical transformations of secondary organic aerosol (SOA) is both a major challenge and the area of greatest uncertainty in current aerosol research. This study presents the first application of desorption electrospray ionization combined with high-resolution mass spectrometry (DESI-MS) for detailed chemical characterization and studies of chemical aging of OA collected on Teflon substrates. DESI-MS offers unique advantages both for detailed characterization of chemically labile components in OA that cannot be detected using more traditional electrospray ionization mass spectrometry (ESI-MS) and for studying chemical aging of OA. DESI-MS enables rapid characterization of OA samples collected on substrates by eliminating the sample preparation stage. In addition, it enables detection and structural characterization of chemically labile molecules in OA samples by minimizing the residence time of analyte in the solvent. SOA produced by the ozonolysis of limonene (LSOA) was allowed to react with gaseous ammonia. Chemical aging resulted in measurable changes in the optical properties of LSOA observed using UV- visible spectroscopy. DESI-MS combined with tandem mass spectrometry experiments (MS/MS) enabled identification of species in aged LSOA responsible for absorption of the visible light. Detailed analysis of the experimental data allowed us to identify chemical changes induced by reactions of LSOA constituents with ammonia and distinguish between different mechanisms of chemical aging.

Laskin, Julia; Laskin, Alexander; Roach, Patrick J.; Slysz, Gordon W.; Anderson, Gordon A.; Nizkorodov, Serguei; Bones, David L.; Nguyen, Lucas

2010-03-01

66

Metastable high-spin states in chemical ionization in hydrocarbon combustion  

SciTech Connect

The chemical ionization mechanism for HCO{sub 2}{sup +} is considered from MINDO/3 CI calculations and ones on the spin-orbit interaction elements, which has been employed in examining the sections of the potential-energy surfaces along the reaction coordinates in the formation of HCO{sub 2}{sup {center_dot}} and HCO{sub 2}{sup +}.

Minaev, B.F.; Ivanova, N.M.; Serov, V.V.

1992-05-01

67

Fundamentals of ambient metastable-induced chemical ionization mass spectrometry and atmospheric pressure ion mobility spectrometry  

NASA Astrophysics Data System (ADS)

Molecular ionization is owed much of its development from the early implementation of electron ionization (EI). Although dramatically increasing the library of compounds discovered, an inherent problem with EI was the low abundance of molecular ions detected due to high fragmentation leading to the difficult task of the correct chemical identification after mass spectrometry (MS). These problems stimulated the research into new ionization methods which sought to "soften" the ionization process. In the late 1980s the advancements of ionization techniques was thought to have reached its pinnacle with both electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). Both ionization techniques allowed for "soft" ionization of large molecular weight and/or labile compounds for intact characterization by MS. Albeit pervasive, neither ESI nor MALDI can be viewed as "magic bullet" ionization techniques. Both techniques require sample preparation which often included native sample destruction, and operation of these techniques took place in sealed enclosures and often, reduced pressure conditions. New open-air ionization techniques termed "ambient MS" enable direct analysis of samples of various physical states, sizes and shapes. One particular technique named Direct Analysis In Real Time (DART) has been steadily growing as one of the ambient tools of choice to ionize small molecular weight (< 1000 Da) molecules with a wide range of polarities. Although there is a large list of reported applications using DART as an ionization source, there have not been many studies investigating the fundamental properties of DART desorption and ionization mechanisms. The work presented in this thesis is aimed to provide in depth findings on the physicochemical phenomena during open-air DART desorption and ionization MS and current application developments. A review of recent ambient plasma-based desorption/ionization techniques for analytical MS is presented in Chapter 1. Chapter 2 presents the first investigations into the atmospheric pressure ion transport phenomena during DART analysis. Chapter 3 provides a comparison on the internal energy deposition processes during DART and pneumatically assisted-ESI. Chapter 4 investigates the complex spatially-dependent sampling sensitivity, dynamic range and ion suppression effects present in most DART experiments. New implementations and applications with DART are shown in Chapters 5 and 6. In Chapter 5, DART is coupled to multiplexed drift tube ion mobility spectrometry as a potential fieldable platform for the detection of toxic industrial chemicals and chemical warfare agents simulants. In Chapter 6, transmission-mode DART is shown to be an effective method for reproducible sampling from materials which allow for gas to flow through it. Also, Chapter 6 provides a description of a MS imaging platform coupling infrared laser ablation and DART-like phenomena. Finally, in Chapter 7 I will provide perspective on the work completed with DART and the tasks and goals that future studies should focus on.

Harris, Glenn A.

68

Fast screening of authentic ginseng products by surface desorption atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Surface desorption atmospheric pressure chemical ionization mass spectrometry was developed as a rapid online detection technology for the chemical fingerprints of ginseng products without any sample pretreatment. More than 20 ginsenosides were detected in the ginseng tissue and identified by their tandem mass spectrometry. Data were well matched with their reference compounds. Herein, surface desorption atmospheric pressure chemical ionization mass spectrometry was first applied to study the nonvolatile compounds in ginseng. White and red ginseng have been successfully differentiated from their counterfeits using some ginsenosides as chemical markers. Ginsenoside can be used to differentiate between white ginseng, red ginseng, unboiled ginseng, and their counterfeits. Ginsenosides Ra1-3, Rb2-3, and Rc might be used to differentiate between white ginseng and boiled ginseng. Our result showed that surface desorption atmospheric pressure chemical ionization mass spectrometry not only could be used for fast screening authentic ginseng products but also might become a useful promising technique for the characterization of nonvolatile compounds in medicinal herbs to save researchers the laborious effort of sample pretreatment. PMID:23212787

Yue, Hao; Ma, Li; Pi, Zifeng; Chen, Huanwen; Wang, Yang; Hu, Bin; Liu, Shuying

2013-01-01

69

Fragmentation of Allylmethylsulfide by Chemical Ionization: Dependence on Humidity and Inhibiting Role of Water  

PubMed Central

We report on a previously unknown reaction mechanism involving water in the fragmentation reaction following chemical ionization. This result stems from a study presented here on the humidity-dependent and energy-dependent endoergic fragmentation of allyl methyl sulfide (AMS) upon protonation in a proton transfer reaction-mass spectrometer (PTR-MS). The fragmentation pathways were studied with experimental (PTR-MS) and quantum chemical methods (polarizable continuum model (PCM), microhydration, studied at the MP2/6-311+G(3df,2p)//MP2/6-31G(d,p) level of theory). We report in detail on the energy profiles, reaction mechanisms, and proton affinities (G4MP2 calculations). In the discovered reaction mechanism, water reduces the fragmentation of protonated species in chemical ionization. It does so by direct interaction with the protonated species via covalent binding (C3H5+) or via association (AMS·H+). This stabilizes intermediate complexes and thus overall increases the activation energy for fragmentation. Water thereby acts as a reusable inhibitor (anticatalyst) in chemical ionization. Moreover, according to the quantum chemical (QC) results, when water is present in abundance it has the opposite effect and enhances fragmentation. The underlying reason is a concentration-dependent change in the reaction principle from active inhibition of fragmentation to solvation, which then enhances fragmentation. This amphoteric behavior of water is found for the fragmentation of C3H5+ to C3H3+, and similarly for the fragmentation of AMS·H+ to C3H5+. The results support humidity-dependent quantification efforts for PTR-MS and chemical ionization mass spectrometry (CIMS). Moreover, the results should allow for a better understanding of ion-chemistry in the presence of water. PMID:23682687

2013-01-01

70

Influence of ionization on the Gupta and on the Park chemical models  

NASA Astrophysics Data System (ADS)

This study is an extension of former works by the present authors, in which the influence of the chemical models by Gupta and by Park was evaluated on thermo-fluid-dynamic parameters in the flow field, including transport coefficients, related characteristic numbers and heat flux on two current capsules (EXPERT and Orion) during the high altitude re-entry path. The results verified that the models, even computing different air compositions in the flow field, compute only slight different compositions on the capsule surface, therefore the difference in the heat flux is not very relevant. In the above mentioned studies, ionization was neglected because the velocities of the capsules (about 5000 m/s for EXPERT and about 7600 m/s for Orion) were not high enough to activate meaningful ionization. The aim of the present work is to evaluate the incidence of ionization, linked to the chemical models by Gupta and by Park, on both heat flux and thermo fluid-dynamic parameters. The present computer tests were carried out by a direct simulation Monte Carlo code (DS2V) in the velocity interval 7600-12000 m/s, considering only the Orion capsule at an altitude of 85 km. The results verified what already found namely when ionization is not considered, the chemical models compute only a slight different gas composition in the core of the shock wave and practically the same composition on the surface therefore the same heat flux. On the opposite, the results verified that when ionization is considered, the chemical models compute different compositions in the whole shock layer and on the surface therefore different heat flux. The analysis of the results relies on a qualitative and a quantitative evaluation of the effects of ionization on both chemical models. The main result of the study is that when ionization is taken into account, the Park model is more reactive than the Gupta model; consequently, the heat flux computed by Park is lower than the one computed by Gupta; using the Gupta model, in the design of a thermal protection system, is recommended.

Morsa, Luigi; Zuppardi, Gennaro

2014-12-01

71

A field-deployable, chemical ionization time-of-flight mass spectrometer  

NASA Astrophysics Data System (ADS)

We constructed a new chemical ionization time-of-flight mass spectrometer (CI-TOFMS) that measures atmospheric trace gases in real time with high sensitivity. We apply the technique to the measurement of formic acid via negative-ion proton transfer, using acetate as the reagent ion. A novel high pressure interface, incorporating two RF-only quadrupoles is used to efficiently focus ions through four stages of differential pumping before analysis with a compact TOFMS. The high ion-duty cycle (>20 %) of the TOFMS combined with the efficient production and transmission of ions in the high pressure interface results in a highly sensitive (>300 ions s-1 pptv-1 formic acid) instrument capable of measuring and saving complete mass spectra at rates faster than 10 Hz. We demonstrate the efficient transfer and detection of both bare ions and ion-molecule clusters, and characterize the instrument during field measurements aboard the R/V Atlantis as part of the CalNex campaign during the spring of 2010. The in-field short-term precision is better than 5 % at 1 pptv (pL/L), for 1-s averages. The detection limit (3 ?, 1-s averages) of the current version of the CI-TOFMS, as applied to the in situ detection of formic acid, is limited by the magnitude and variability in the background determination and was determined to be 4 pptv. Application of the CI-TOFMS to the detection of other inorganic and organic acids, as well as the use of different reagent ion molecules (e.g. I-, CF3O-, CO3-) is promising, as we have demonstrated efficient transmission and detection of both bare ions and their associated ion-molecule clusters.

Bertram, T. H.; Kimmel, J. R.; Crisp, T. A.; Ryder, O. S.; Yatavelli, R. L. N.; Thornton, J. A.; Cubison, M. J.; Gonin, M.; Worsnop, D. R.

2011-07-01

72

Evaluating the Utility of an Atmospheric Pressure Chemical Ionization Mass Spectrometer for Analyzing Organic Peroxides  

NASA Astrophysics Data System (ADS)

Secondary organic aerosols (SOA) are known to affect the earth's radiation budget through its ability to scatter and absorb radiation. Consequently, the mechanisms and factors that influence SOA composition and formation are poorly understood. However, recent modeling studies coupled with smog chamber experiments suggest that organic peroxides (organic hydroperoxides and peroxyhemiacetals) might be a major component of SOA composition under low NOx conditions. This study utilized an atmospheric pressure chemical ionization mass spectrometer (APCI-MS) in the positive mode to detect organic peroxides. Mass spectra of organic peroxides analyzed in this study show excessive fragmentation during ionization with protonated water clusters. It was believed that intact ions were not found due to decomposition in the ion source. Future work will explore new reagents for ionization to reduce fragmentation during analysis.

Jameer, A.; Hastie, D. R.

2013-12-01

73

Alternative Methodology for Boron Isotopic Analysis of CaCO3 by Negative Thermal Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Negative thermal ionization mass spectrometry (NTIMS) has been a common tool for investigating boron isotopes in CaCO3 and other environmental samples, the high sensitivity of BO2- ionization enabling measurements of ng levels of boron. However, B isotope measurement by this technique suffers from a number of problems, including: (1) fractionation induced by selective ionization of B isotopes in the mass spectrometer; (2) CNO- interference on mass 42 ([10BO2]-) that may be present in some filament load solutions (such as B-free seawater processed through ion-exchange resin), and (3) potential matrix effects due to widely differing chemistry of samples and standards. Here we examine a potentially improved NTIMS methodology that incudes removal of sample-related calcium (and other cations) by ion exchange and uses an alternative filament loading solution prepared from high-purity single-element solutions of Ca, Mg, Na, and K. Initial results suggest that this new method may offer significant improvement over the more traditional NTIMS approach in which digested CaCO3 samples are directly loaded onto filaments in B-free seawater. Replicate analyses of standards and samples yield a typical standard deviation of approximately 0.3‰ ?11B and boron isotopic compositions comparable to reported or consensus values. Fractionation during analysis has thus far typically been less than 0.5‰ ?11B. The method delivers boron ionization efficiency similar to directly-loaded seawater, and negligible signal at mass 26 (CN-), a proxy for the possible interfering molecular CNO- ion. Standards and samples behave similarly and predictably during filament heating and analysis, thus allowing for fully automated data acquisition, which in turn may increase sample throughput and reduce potential analytical inconsistencies associated with operator-controlled heating and analysis.

Dwyer, G. S.; Vengosh, A.

2012-12-01

74

Characterization of triacetone triperoxide by ion mobility spectrometry and mass spectrometry following atmospheric pressure chemical ionization  

SciTech Connect

The atmospheric pressure chemical ionization of triacetone triperoxide (TATP) with subsequent separation and detection by ion mobility spectrometry has been studied. Positive ionization with hydronium reactant ions produced only fragments of the TATP molecule, with m/z 91 ion being the most predominant species. Ionization with ammonium reactant ions produced a molecular adduct at m/z 240. The reduced mobility value of this ion was constant at 1.36 cm{sup 2}V{sup -1}s{sup -1} across the temperature range from 60 to 140 C. The stability of this ion was temperature dependent and did not exist at temperatures above 140 C, where only fragment ions were observed. The introduction of ammonia vapors with TATP resulted in the formation of m/z 58 ion. As the concentration of ammonia increased, this smaller ion appeared to dominate the spectra and the TATP-ammonium adduct decreased in intensity. The ion at m/z 58 has been noted by several research groups upon using ammonia reagents in chemical ionization, but the identity was unknown. Evidence presented here supports the formation of protonated 2-propanimine. A proposed mechanism involves the addition of ammonia to the TATP-ammonium adduct followed by an elimination reaction. A similar mechanism involving the chemical ionization of acetone with excess ammonia also showed the formation of m/z 58 ion. TATP vapors from a solid sample were detected with a hand-held ion mobility spectrometer operated at room temperature. The TATP-ammonium molecular adduct was observed in the presence of ammonia and TATP vapors with this spectrometer.

Ewing, Robert G.; Waltman, Melanie J.; Atkinson, David A.

2011-04-28

75

Atmospheric pressure chemical ionization studies of non-polar isomeric hydrocarbons using ion mobility spectrometry and mass spectrometry with different ionization techniques  

NASA Technical Reports Server (NTRS)

The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis/trans isomers) using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization to assess the influence of structural features on ion formation. Depending on the structural features, different ions were observed using mass spectrometry. Unsaturated hydrocarbons formed mostly [M - 1]+ and [(M - 1)2H]+ ions while mainly [M - 3]+ and [(M - 3)H2O]+ ions were found for saturated cis/trans isomers using photoionization and 63Ni ionization. These ionization methods and corona discharge ionization were used for ion mobility measurements of these compounds. Different ions were detected for compounds with different structural features. 63Ni ionization and photoionization provide comparable ions for every set of isomers. The product ions formed can be clearly attributed to the structures identified. However, differences in relative abundance of product ions were found. Although corona discharge ionization permits the most sensitive detection of non-polar hydrocarbons, the spectra detected are complex and differ from those obtained with 63Ni ionization and photoionization. c. 2002 American Society for Mass Spectrometry.

Borsdorf, H.; Nazarov, E. G.; Eiceman, G. A.

2002-01-01

76

Real-time monitoring of volatile organic compounds using chemical ionization mass spectrometry  

DOEpatents

A system for on-line quantitative monitoring of volatile organic compounds (VOCs) includes pressure reduction means for carrying a gaseous sample from a first location to a measuring input location maintained at a low pressure, the system utilizing active feedback to keep both the vapor flow and pressure to a chemical ionization mode mass spectrometer constant. A multiple input manifold for VOC and gas distribution permits a combination of calibration gases or samples to be applied to the spectrometer.

Mowry, Curtis Dale (Albuquerque, NM); Thornberg, Steven Michael (Peralta, NM)

1999-01-01

77

Electron impact and chemical ionization mass spectral analysis of a volatile uranyl derivative  

SciTech Connect

Quadrupole mass spectral analysis of the volatile uranium ligand complex bis (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) dioxouranium-di-n-butyl sulfoxide is described utilizing electron impact (EI) and methane chemical ionization (CI) ion sources. All major ions are tentatively identified and the potential usefulness of this complex for determining uranium isotope /sup 235/U//sup 238/U abundance is demonstrated.

Reutter, D.J.; Hardy, D.R.

1981-01-01

78

Atmospheric pressure chemical ionization (APcI) liquid chromatography-mass spectrometry: characterization of natural antioxidants  

Microsoft Academic Search

The combination of liquid chromatography with mass spectrometry (LC-MS) allows non-volatile and thermally sensitive compounds to be handled. The key feature, regarding LC flowrate and MS vacuum requirements, is the LC-MS interface system. Atmospheric pressure chemical ionization (APcI) is a sensitive and widely applicable method which gives primarily molecular weight information with the ability to provide structural information if required.

M.-N. Maillard; P. Giampaoli; M.-E. Cuvelier

1996-01-01

79

Differentiation of commercial fuels based on polar components using negative electrospray ionization/mass spectrometry  

USGS Publications Warehouse

Polar components in fuels may enable differentiation between fuel types or commercial fuel sources. A range of commercial fuels from numerous sources were analyzed by flow injection analysis/electrospray ionization/mass spectrometry without extensive sample preparation, separation, or chromatography. This technique enabled screening for unique polar components at parts per million levels in commercial hydrocarbon products, including a range of products from a variety of commercial sources and locations. Because these polar compounds are unique in different fuels, their presence may provide source information on hydrocarbons released into the environment. This analysis was then applied to mixtures of various products, as might be found in accidental releases into the environment. Copyright ?? Taylor & Francis Group, LLC.

Rostad, C.E.

2006-01-01

80

DETERMINATION OF PHTHALATES IN WATER AND SOIL BY TANDEM MASS SPECTROMETRY UNDER CHEMICAL IONIZATION CONDITIONS WITH ISOBUTANE AS REAGENT GAS  

EPA Science Inventory

Phthalate determination is important because phthalates often are major impurities in samples and can have significant health effects. Tandem mass spectrometry under chemical ionization mass spectrometry conditions with isobutane as the reagent gas was used to determine 11 phthal...

81

Laser-Induced Acoustic Desorption/Atmospheric Pressure Chemical Ionization Mass Spectrometry  

PubMed Central

Laser-induced acoustic desorption (LIAD) was successfully coupled to a conventional atmospheric pressure chemical ionization (APCI) source in a linear quadrupole ion trap mass spectrometer (LQIT). Model compounds representing a wide variety of different types, including basic nitrogen and oxygen compounds, aromatic and aliphatic compounds, as well as unsaturated and saturated hydrocarbons, were tested separately and as a mixture. These model compounds were successfully evaporated into the gas phase by using LIAD and then ionized by using APCI with different reagents. Four APCI reagent systems were tested: the traditionally used mixture of methanol and water, neat benzene, neat carbon disulfide, and nitrogen gas (no liquid reagent). The mixture of methanol and water produced primarily protonated molecules, as expected. However, only the most basic compounds yielded ions under these conditions. In sharp contrast, using APCI with either neat benzene or neat carbon disulfide as the reagent resulted in the ionization of all the analytes studied to predominantly yield stable molecular ions. Benzene yielded a larger fraction of protonated molecules than carbon disulfide, which is a disadvantage. A similar amount of fragmentation was observed for these reagents. When the experiment was performed without a liquid reagent(nitrogen gas was the reagent), more fragmentation was observed. Analysis of a known mixture as well as a petroleum cut was also carried out. In summary, the new experiment presented here allows the evaporation of thermally labile compounds, both polar and nonpolar, without dissociation or aggregation, and their ionization to form stable molecular ions. PMID:21472571

Gao, Jinshan; Borton, David J.; Owen, Benjamin C.; Jin, Zhicheng; Hurt, Matt; Amundson, Lucas M.; Madden, Jeremy T.; Qian, Kuangnan; Kenttämaa, Hilkka I.

2010-01-01

82

Negative electrospray ionization mass spectrometry: a method for sequencing and determining linkage position in oligosaccharides from branched hemicelluloses.  

PubMed

Xyloglucans of apple, tomato, bilberry and tamarind were hydrolyzed by commercial endo ?-1-4-D-endoglucanase. The xylo-gluco-oligosaccharides (XylGos) released were separated on CarboPac PA 200 column in less than 15?min, and, after purification, they were structurally characterized by negative electrospray ionization mass spectrometry using a quadrupole time-of-flight (ESI-Q-TOF), a hybrid linear ion trap (LTQ)/Orbitrap and a hybrid quadrupole Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers. In order to corroborate the fragmentation routes observed on XylGos, some commercial galacto-manno-oligosaccharides (GalMOs) and glucurono-xylo-oligosaccharides were also studied. The fragmentation pathways of the ionized GalMos were similar to those of XylGos ones. The product ion spectra were mainly characterized by prominent double cleavage (D) ions corresponding to the entire inner side chains. The directed fragmentation from the reducing end to the other end was observed for the main glycosylated backbone but also for the side-chains, allowing their complete sequencing. Relevant cross-ring cleavage ions from (0,2) Xj -type revealed to be diagnostic of the 1-2-linked- glycosyl units from XylGos together with the 1-2-linked glucuronic acid unit from glucuronoxylans. Resonant activation in the LTQ Orbitrap allowed not only determining the type of all linkages but also the O-acetyl group location on fucosylated side-chains. Moreover, the fragmentation of the different side chains using the MS(n) capabilities of the LTQ/Orbitrap analyzer also allowed differentiating terminal arabinosyl and xylosyl substituents inside S and U side-chains of XylGos, respectively. The CID spectra obtained were very informative for distinction of isomeric structures differing only in their substitution pattern. These features together makes the fragmentation in negative ionization mode a relevant and powerful technique useful to highlight the subtle structural changes generally observed during the development of plant organs such as during fruit ripening and for the screening of cell wall mutants with altered hemicellulose structure. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25601700

Quéméner, Bernard; Vigouroux, Jacqueline; Rathahao, Estelle; Tabet, Jean Claude; Dimitrijevic, Aleksandra; Lahaye, Marc

2015-01-01

83

Carbon disulfide reagent allows the characterization of nonpolar analytes by atmospheric pressure chemical ionization mass spectrometry.  

PubMed

While atmospheric pressure ionization methodologies have revolutionized the mass spectrometric analysis of nonvolatile analytes, limitations native to the chemistry of these methodologies hinder or entirely inhibit the analysis of certain analytes, specifically, many nonpolar compounds. Examination of various analytes, including asphaltene and lignin model compounds as well as saturated hydrocarbons, demonstrates that atmospheric pressure chemical ionization (APCI) using CS(2) as the reagent produces an abundant and stable molecular ion (M(+•)) for all model compounds studied, with the exception of completely saturated aliphatic hydrocarbons and the two amino acids tested, arginine and phenylalanine. This reagent substantially broadens the applicability of mass spectrometry to nonvolatile nonpolar analytes and also facilitates the examination of radical cation chemistry by mass spectrometry. PMID:21698674

Owen, Benjamin C; Gao, Jinshan; Borton, David J; Amundson, Lucas M; Archibold, Enada F; Tan, Xiaoli; Azyat, Khalid; Tykwinski, Rik; Gray, Murray; Kenttämaa, Hilkka I

2011-07-30

84

Collision-Induced Dissociation Analysis of Negative Atmospheric Ion Adducts in Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Collision-induced dissociation (CID) experiments were performed on atmospheric ion adducts [M + R]- formed between various types of organic compounds M and atmospheric negative ions R- [such as O2 -, HCO3 -, COO-(COOH), NO2 -, NO3 -, and NO3 -(HNO3)] in negative-ion mode atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. All of the [M + R]- adducts were fragmented to form deprotonated analytes [M - H]- and/or atmospheric ions R-, whose intensities in the CID spectra were dependent on the proton affinities of the [M - H]- and R- fragments. Precursor ions [M + R]- for which R- have higher proton affinities than [M - H]- formed [M - H]- as the dominant product. Furthermore, the CID of the adducts with HCO3 - and NO3 -(HNO3) led to other product ions such as [M + HO]- and NO3 -, respectively. The fragmentation behavior of [M + R]- for each R- observed was independent of analyte type (e.g., whether the analyte was aliphatic or aromatic, or possessed certain functional groups).

Sekimoto, Kanako; Takayama, Mitsuo

2013-05-01

85

Atmospheric pressure chemical ionization of fluorinated phenols in atmospheric pressure chemical ionization mass spectrometry, tandem mass spectrometry, and ion mobility spectrometry  

NASA Technical Reports Server (NTRS)

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) for fluorinated phenols (C6H5-xFxOH Where x = 0-5) in nitrogen with Cl- as the reagent ion yielded product ions of M Cl- through ion associations or (M-H)- through proton abstractions. Proton abstraction was controllable by potentials on the orifice and first lens, suggesting that some proton abstraction occurs through collision induced dissociation (CID) in the interface region. This was proven using CID of adduct ions (M Cl-) with Q2 studies where adduct ions were dissociated to Cl- or proton abstracted to (M-H)-. The extent of proton abstraction depended upon ion energy and structure in order of calculated acidities: pentafluorophenol > tetrafluorophenol > trifluorophenol > difluorophenol. Little or no proton abstraction occurred for fluorophenol, phenol, or benzyl alcohol analogs. Ion mobility spectrometry was used to determine if proton abstraction reactions passed through an adduct intermediate with thermalized ions and mobility spectra for all chemicals were obtained from 25 to 200 degrees C. Proton abstraction from M Cl- was not observed at any temperature for phenol, monofluorophenol, or difluorophenol. Mobility spectra for trifluorophenol revealed the kinetic transformations to (M-H)- either from M Cl- or from M2 Cl- directly. Proton abstraction was the predominant reaction for tetra- and penta-fluorophenols. Consequently, the evidence suggests that proton abstraction occurs from an adduct ion where the reaction barrier is reduced with increasing acidity of the O-H bond in C6H5-xFxOH.

Eiceman, G. A.; Bergloff, J. F.; Rodriguez, J. E.; Munro, W.; Karpas, Z.

1999-01-01

86

Real-time monitoring of volatile organic compounds using chemical ionization mass spectroscopy: Final report  

SciTech Connect

Volatile organic compound (VOC) emission to the atmosphere is of great concern to semiconductor manufacturing industries, research laboratories, the public, and regulatory agencies. Some industries are seeking ways to reduce emissions by reducing VOCs at the point of use (or generation). This paper discusses the requirements, design, calibration, and use of a sampling inlet/quadrupole mass spectrometer system for monitoring VOCs in a semiconductor manufacturing production line. The system uses chemical ionization to monitor compounds typically found in the lithography processes used to manufacture semiconductor devices (e.g., acetone, photoresist). The system was designed to be transportable from tool to tool in the production line and to give the operator real-time feedback so the process(es) can be adjusted to minimize VOC emissions. Detection limits ranging from the high ppb range for acetone to the low ppm range fore other lithography chemicals were achieved using chemical ionization mass spectroscopy at a data acquisition rate of approximately 1 mass spectral scan (30 to 200 daltons) per second. A demonstration of exhaust VOC monitoring was performed at a working semiconductor fabrication facility during actual wafer processing.

Thornberg, S.M.; Mowry, C.D.; Keenan, M.R.; Bender, S.F.A. [Sandia National Labs., Albuquerque, NM (United States). Gas Analysis Lab.; Owen, T. [Intel Corp., Rio Rancho, NM (United States)

1997-04-01

87

Negative Electron Affinity Effect on the Surface of Chemical Vapor Deposited Diamond Polycrystalline Films  

NASA Technical Reports Server (NTRS)

Strong negative electron affinity effects have been observed on the surface of as-grown chemical vapor deposited diamond using Secondary Electron Emission. The test samples were randomly oriented and the surface was terminated with hydrogen. The effect appears as an intensive peak in the low energy part of the spectrum of the electron energy distribution and may be described in the model of effective negative electron affinity.

Krainsky, I. L.; Asnin, V. M.; Mearini, G. T.; Dayton, J. A., Jr.

1996-01-01

88

Thin-layer chromatography and mass spectrometry coupled using proximal probe thermal desorption with electrospray or atmospheric pressure chemical ionization.  

PubMed

An atmospheric pressure proximal probe thermal desorption sampling method coupled with secondary ionization by electrospray or atmospheric pressure chemical ionization was demonstrated for the mass spectrometric analysis of a diverse set of compounds (dyestuffs, pharmaceuticals, explosives and pesticides) separated on various high-performance thin-layer chromatography plates. Line scans along or through development lanes on the plates were carried out by moving the plate relative to a stationary heated probe positioned close to or just touching the stationary phase surface. Vapors of the compounds thermally desorbed from the surface were drawn into the ionization region of a combined electrospray ionization/atmospheric pressure chemical ionization source where they merged with reagent ions and/or charged droplets from a corona discharge or an electrospray emitter and were ionized. The ionized components were then drawn through the atmospheric pressure sampling orifice into the vacuum region of a triple quadrupole mass spectrometer and detected using full scan, single ion monitoring, or selected reaction monitoring mode. Studies of variable parameters and performance metrics including the proximal probe temperature, gas flow rate into the ionization region, surface scan speed, read-out resolution, detection limits, and surface type are discussed. PMID:20499315

Ovchinnikova, Olga S; Van Berkel, Gary J

2010-06-30

89

Photochemistry of limonene secondary organic aerosol studied with chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Limonene is one of the most abundant monoterpenes in the atmosphere. Limonene easily reacts with gas-phase oxidants in air such as NO3, ozone and OH. Secondary organic aerosol (SOA) is formed when low vapor pressure products condense into particles. Chemicals in SOA particles can undergo further reactions with oxidants and with solar radiation that significantly change SOA composition over the course of several days. The goal of this work was to characterize radiation induced reaction in SOA. To perform experiments, we have designed and constructed an Atmospheric Pressure Chemical Ionization Mass Spectrometer (APCIMS) coupled to a photochemical cell containing SOA samples. In APCIMS, (H2O)nH 3O+ clusters are generated in a 63Ni source and react with gaseous organic analytes. Most organic chemicals are not fragmented by the ionization process. We have focused our attention on limonene SOA prepared in two different ways. The first type of SOA is produced by oxidation of limonene by ozone; and the second type of SOA is formed by the NO3-induced oxidation of limonene. They model the SOA formed under daytime and nighttime conditions, respectively. Ozone initiated oxidation is the most important chemical sink for limonene both indoors, where it is used for cleaning purposes, and outdoors. Terpenes are primarily oxidized by reactions with NO3 at night time. We generated limonene SOA under different ozone and limonene concentrations. The resulting SOA samples were exposed to wavelength-tunable radiation in the UV-Visible range between 270 nm and 630 nm. The results show that the photodegradation rates strongly depend on radiation wavelengths. Gas phase photodegradation products such as acetone, formaldehyde, acetaldehyde, and acetic acid were shown to have different production rates for SOA formed in different concentration conditions. Even for SOA prepared under the lowest concentrations, the SOA photodegradation was efficient. The conclusion is that exposure of SOA to solar radiation causes significant chemical aging in SOA species.

Pan, Xiang

90

Picoelectrospray Ionization Mass Spectrometry Using Narrow-Bore Chemically Etched Emitters  

NASA Astrophysics Data System (ADS)

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored because of difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, whereas the signal decreases monotonically with decreasing flow rates at higher concentrations. For example, consumption of 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. In spite of lower MS signal, the ion utilization efficiency increases exponentially with decreasing flow rate in all cases. Significant variations in ionization efficiency were observed within this flow rate range for an equimolar mixture of peptide, indicating that ionization efficiency is an analyte-dependent characteristic for the present experimental conditions. Mass-limited samples benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. These findings have important implications for the analysis of trace biological samples.

Marginean, Ioan; Tang, Keqi; Smith, Richard D.; Kelly, Ryan T.

2014-01-01

91

Modifying the Charge State Distribution of Proteins in Electrospray Ionization Mass Spectrometry by Chemical Derivatization  

PubMed Central

Electrospray ionization (ESI) of denatured proteins produces a broad distribution of multiply-charged ions leading to multiple peaks in the mass spectrum. We investigated changes in the positive-mode ESI charge state distribution produced by several chemical modifications of denatured proteins. Capping carboxylic acid groups with neutral functional groups yields little change in charge state distribution compared to unmodified proteins. The results indicate that carboxyl groups do not play a significant role in the positive charging of denatured proteins in ESI. The modification of proteins with additional basic sites or fixed positive charges generates substantially higher charge states, providing evidence that the number of ionizable sites, rather than molecular size and shape, determines ESI charging for denatured proteins. Fixed charge modification also significantly reduces the number of protons acquired by a protein, in that the charge state envelope is not increased by the full number of fixed charges appended. This result demonstrates that Coulombic repulsion between positive charges plays a significant role in determining charge state distribution by affecting the gas-phase basicity of ionizable sites. Addition of fixed-charge moieties to a protein is a useful approach for shifting protein charge state distributions to higher charge states, and with further work, it may help limit the distribution of protein ions to fewer charge states. PMID:19481956

Krusemark, Casey J.; Frey, Brian L.; Belshaw, Peter J.

2009-01-01

92

Picoelectrospray ionization mass spectrometry using narrow-bore chemically etched emitters  

PubMed Central

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored due to difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, while the signal decreases monotonically with decreasing flow rates at higher concentrations. For example, consumption of 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. In spite of lower MS signal, the ion utilization efficiency increases exponentially with decreasing flow rate in all cases. Significant variations in ionization efficiency were observed within this flow rate range for an equimolar mixture of peptides, indicating that ionization efficiency is an analyte-dependent characteristic for the present experimental conditions. Mass-limited samples benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. These findings have important implications for the analysis of trace biological samples. PMID:24122304

Marginean, Ioan; Tang, Keqi; Smith, Richard D.; Kelly, Ryan T.

2013-01-01

93

Bio-oil Analysis Using Negative Electrospray Ionization: Comparative Study of High-Resolution Mass Spectrometers and Phenolic versus Sugaric Components  

SciTech Connect

We have previously demonstrated that a petroleomic analysis could be performed for bio-oils and revealed the complex nature of bio-oils for the nonvolatile phenolic compounds (Smith, E.; Lee, Y. J. Energy Fuels 2010, 24, 5190?5198). As a subsequent study, we have adapted electrospray ionization in negative-ion mode to characterize a wide variety of bio-oil compounds. A comparative study of three common high-resolution mass spectrometers was performed to validate the methodology and to investigate the differences in mass discrimination and resolution. The mass spectrum is dominated by low mass compounds with m/z of 100–250, with some compounds being analyzable by gas chromatography–mass spectrometry (GC–MS). We could characterize over 800 chemical compositions, with only about 40 of them being previously known in GC–MS. This unveiled a much more complex nature of bio-oils than typically shown by GC–MS. The pyrolysis products of cellulose and hemicellulose, particularly polyhydroxy cyclic hydrocarbons (or what we call “sugaric” compounds), such as levoglucosan, could be effectively characterized with this approach. Phenolic compounds from lignin pyrolysis could be clearly distinguished in a contour map of double bond equivalent (DBE) versus the number of carbons from these sugaric compounds.

Smith, Erica A.; Park, Soojin; Klein, Adam T.; Lee, Young Jin

2012-05-16

94

Rapid differentiation of tea products by surface desorption atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Protonated water molecules generated by an ambient corona discharge were directed to impact tea leaves for desorption/ionization at atmospheric pressure. Thus, a novel method based on surface desorption chemical ionization mass spectrometry (DAPCI-MS) has been developed for rapid analysis of tea products without any sample pretreatment. Under the optimized experimental conditions, DAPCI MS spectra of various tea samples are recorded rapidly, and the resulting mass spectra are chemical fingerprints that characterize the tea samples. On the basis of the mass spectral fingerprints, 40 tea samples including green tea, oolong tea, and jasmine tea were successfully differentiated by principal component analysis (PCA) of the mass spectral raw data. The PCA results were also validated with cluster analysis and supervised PCA analysis. The alteration of signal intensity caused by rough surfaces of tea leaves did not cause failure in the separation of the tea products. The experimental findings show that DAPCI-MS creates ions of both volatile and nonvolatile compounds in tea products at atmospheric pressure, providing a practical and convenient tool for high-throughput differentiation of tea products. PMID:18020412

Chen, Huanwen; Liang, Huazheng; Ding, Jianhua; Lai, Jinhu; Huan, Yanfu; Qiao, Xiaolin

2007-12-12

95

Laser Microdissection and Atmospheric Pressure Chemical Ionization Mass Spectrometry Coupled for Multimodal Imaging  

SciTech Connect

This paper describes the coupling of ambient laser ablation surface sampling, accomplished using a laser capture microdissection system, with atmospheric pressure chemical ionization mass spectrometry for high spatial resolution multimodal imaging. A commercial laser capture microdissection system was placed in close proximity to a modified ion source of a mass spectrometer designed to allow for sampling of laser ablated material via a transfer tube directly into the ionization region. Rhodamine 6G dye of red sharpie ink in a laser etched pattern as well as cholesterol and phosphatidylcholine in a cerebellum mouse brain thin tissue section were identified and imaged from full scan mass spectra. A minimal spot diameter of 8 m was achieved using the 10X microscope cutting objective with a lateral oversampling pixel resolution of about 3.7 m. Distinguishing between features approximately 13 m apart in a cerebellum mouse brain thin tissue section was demonstrated in a multimodal fashion including co-registered optical and mass spectral chemical images.

Lorenz, Matthias [ORNL; Ovchinnikova, Olga S [ORNL; Kertesz, Vilmos [ORNL; Van Berkel, Gary J [ORNL

2013-01-01

96

Novel non-chemically amplified (n-CARs) negative resists for EUVL  

NASA Astrophysics Data System (ADS)

We report the lithography performance of novel non chemical amplified (n-CARS) negative photoresist materials which are accomplished by homopolymers and copolymers that are prepared from monomers containing sulfonium groups. The latter have long been found to be sensitive to UV radiation and undergo polarity change on exposure. For this reason, these groups were chosen as radiation sensitive groups in non- CARs that are discussed herein. Novel n-CAR negative resists were synthesized and characterized for EUVL applications, as they are directly sensitive to radiation without utilizing the concept of chemical amplification. The n-CARs achieved 20 and 16 nm L/2S, L/S patterns to meet the ITRS requirements. We will also discuss the sensitivity and LER of these negative n-CARS to e-beam irradiation which will provide a basis for EUVL down to the 16 nm node and below. These new negative tone resist provide a viable path forward for designing non- chemically amplified resists that can obtain higher resolutions than current chemically amplified resists at competitive sensitivities.

Singh, Vikram; Satyanarayana, V. S. V.; Sharma, Satinder K.; Ghosh, Subrata; Gonsalves, Kenneth E.

2014-03-01

97

Charge Enhancement of Single-Stranded DNA in Negative Electrospray Ionization Using the Supercharging Reagent Meta-nitrobenzyl Alcohol  

NASA Astrophysics Data System (ADS)

Charge enhancement of single-stranded oligonucleotide ions in negative ESI mode is investigated. The employed reagent, meta-nitrobenzyl alcohol (m-NBA), was found to improve total signal intensity (Itot), increase the highest observed charge states (zhigh), and raise the average charge states (zavg) of all tested oligonucleotides analyzed in negative ESI. To quantify these increases, signal enhancement ratios (SER1%) and charge enhancement coefficients (CEC1%) were introduced. The SER1%, (defined as the quotient of total oligonucleotide ion abundances with 1 % m-NBA divided by total oligonucleotide abundance without m-NBA) was found to be greater than unity for every oligonucleotide tested. The CEC1% values (defined as the average charge state in the presence of 1 % m-NBA minus the average charge state in the absence of m-NBA) were found to be uniformly positive. Upon close inspection, the degree of charge enhancement for longer oligonucleotides was found to be dependent upon thymine density (i.e., the number and the location of phospho-thymidine units). A correlation between the charge enhancement induced by the presence of m-NBA and the apparent gas-phase acidity (largely determined by the sequence of thymine units but also by the presence of protons on other nucleobases) of multiply deprotonated oligonucleotide species, was thus established. Ammonium cations appeared to be directly involved in the m-NBA supercharging mechanism, and their role seems to be consistent with previously postulated ESI mechanisms describing desorption/ionization of single-stranded DNA into the gas phase.

Brahim, Bessem; Alves, Sandra; Cole, Richard B.; Tabet, Jean-Claude

2013-12-01

98

Determination of organic acids in ground water by liquid chromatography/atmospheric pressure chemical ionization/mass spectrometry  

SciTech Connect

Current methods of determining organic acids in ground water are labor-intensive, time-consuming and require a large volume of sample (100 milliliter to 1.0 liter). This paper reports a new method developed to determine aliphatic, alicyclic, and aromatic acids in ground water using liquid chromatography/atmospheric pressure chemical ionization/mass spectrometry (LC/APCI/MS). This method was shown to be fast (less than 1 hour), effective, and reproducible, requiring only 1.0 mL of ground-water sample. Ground water was pH-adjusted, filtered through 0.45 {micro}m filters and directly injected into the LC. A binary solvent system consisting of 40 mM of aqueous ammonium acetate and methanol and a C18 column were used for chromatographical separation. The APCI was operated under negative ionization mode. Selected ion monitoring (SIM) was used for detection and quantitation of the analytes. This method was applied to the analysis of organic acids in ground-water samples collected from an aquifer contaminated with JP-4 fuel hydrocarbons at Wurtsmith Air Force Base in Oscoda, Michigan. Aromatic acids identified in the contaminated ground water include o-, m-toluic acids (2- and 3-methylbenzoic acids), 2,6-dimethylbenzoic acid, 2,3,5-and 2,4,6-trimethylbenzoic acids and two additional trimethylbenzoic acids with unknown location of methylation. The detection of aromatic acids in groundwater from the KC-135 site provided evidence for in situ microbial degradation of hydrocarbons occurring in the aquifer.

Fang, J.; Barcelona, M.J. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Civil and Environmental Engineering

1999-05-01

99

Capillary electrophoresis-atmospheric pressure chemical ionization-mass spectrometry using an orthogonal interface: set-up and system parameters.  

PubMed

The feasibility of atmospheric pressure chemical ionization (APCI) as an alternative ionization technique for capillary electrophoresis-mass spectrometry (CE-MS) was investigated using a grounded sheath-flow CE-MS sprayer and an orthogonal APCI source. Infusion experiments indicated that highest analyte signals were achieved when the sprayer tip was in close vicinity of the vaporizer entrance. The APCI-MS set-up enabled detection of basic, neutral, and acidic compounds, whereas apolar and ionic compounds could not be detected. In the positive ion mode, analytes could be detected in the entire transfer voltage range (0-5 kV), whereas highest signal intensities were observed when the corona discharge current was between 1000 and 2000 nA. In the negative ion mode, the transfer voltage typically was 500 V and the optimum corona discharge current was 6000 nA. Analyte signals were raised with increasing nebulizing gas pressure, but the pressure was limited to 25 psi to avoid siphoning and current drops. Signal intensities appeared to be optimal and constant over a wide range of sheath liquid flow rate (5-25 microL/min) and vaporizer temperature (200-350 degrees C). APCI-MS signals were unaffected by the composition of the background electrolyte (BGE), even when it contained sodium phosphate and sodium dodecyl sulfate (SDS). Consequently, BGE composition, sheath-liquid flow rate, and vaporizer temperature can be optimized with respect to the CE separation without affecting the APCI-MS response. The analysis of a mixture of basic compounds and a steroid using volatile and nonvolatile BGEs further demonstrates the feasibility of CE-APCI-MS. Detection limits (S/N = 3) were 1.6-10 microM injected concentrations. PMID:19349196

Hommerson, Paul; Khan, Amjad M; de Jong, Gerhardus J; Somsen, Govert W

2009-07-01

100

An added dimension: GC atmospheric pressure chemical ionization FTICR MS and the Athabasca oil sands.  

PubMed

The Athabasca oil sands industry, an alternative source of petroleum, uses large quantities of water during processing of the oil sands. In keeping with Canadian environmental policy, the processed water cannot be released to natural waters and is thus retained on-site in large tailings ponds. There is an increasing need for further development of analytical methods for environmental monitoring. The following details the first example of the application of gas chromatography atmospheric pressure chemical ionization Fourier transform ion cyclotron resonance mass spectrometry (GC-APCI-FTICR MS) for the study of environmental samples from the Athabasca region of Canada. APCI offers the advantages of reduced fragmentation compared to other ionization methods and is also more amenable to compounds that are inaccessible by electrospray ionization. The combination of GC with ultrahigh resolution mass spectrometry can improve the characterization of complex mixtures where components cannot be resolved by GC alone. This, in turn, affords the ability to monitor extracted ion chromatograms for components of the same nominal mass and isomers in the complex mixtures. The proof of concept work described here is based upon the characterization of one oil sands process water sample and two groundwater samples in the area of oil sands activity. Using the new method, the Ox and OxS compound classes predominated, with OxS classes being particularly relevant to the oil sands industry. The potential to resolve retention times for individual components within the complex mixture, highlighting contributions from isomers, and to characterize retention time profiles for homologous series is shown, in addition to the ability to follow profiles of double bond equivalents and carbon number for a compound class as a function of retention time. The method is shown to be well-suited for environmental forensics. PMID:25036898

Barrow, Mark P; Peru, Kerry M; Headley, John V

2014-08-19

101

Kinetic and Thermodynamic Control of Protonation in Atmospheric Pressure Chemical Ionization  

NASA Astrophysics Data System (ADS)

For p-(dimethylamino)chalcone ( p-DMAC), the N atom is the most basic site in the liquid phase, whereas the O atom possesses the highest proton affinity in the gas phase. A novel and interesting observation is reported that the N- and O-protonated p-DMAC can be competitively produced in atmospheric pressure chemical ionization (APCI) with the change of solvents and ionization conditions. In neat methanol or acetonitrile, the protonation is always under thermodynamic control to form the O-protonated ion. When methanol/water or acetonitrile/water was used as the solvent, the protonation is kinetically controlled to form the N-protonated ion under conditions of relatively high infusion rate and high concentration of water in the mixed solvent. The regioselectivity of protonation of p-DMAC in APCI is probably attributed to the bulky solvent cluster reagent ions (SnH+) and the analyte having different preferred protonation sites in the liquid phase and gas phase.

Chai, Yunfeng; Hu, Nan; Pan, Yuanjiang

2013-07-01

102

Picoelectrospray Ionization Mass Spectrometry Using Narrow-bore Chemically Etched Emitters  

SciTech Connect

Electrospray ionization mass spectrometry (ESI-MS) at flow rates below ~10 nL/min has been only sporadically explored due to difficulty in reproducibly fabricating emitters that can operate at lower flow rates. Here we demonstrate narrow orifice chemically etched emitters for stable electrospray at flow rates as low as 400 pL/min. Depending on the analyte concentration, we observe two types of MS signal response as a function of flow rate. At low concentrations, an optimum flow rate is observed slightly above 1 nL/min, while the signal decreases monotonically with decreasing flow rates at higher concentrations. In spite of lower MS signal, the ion utilization efficiency increases exponentially with decreasing flow rate in all cases. No unimolecular response was observed within this flow rate range during the analysis of an equimolar mixture of peptides, indicating that ionization efficiency is an analyte-dependent characteristic in given experimental conditions. While little to no gain in signal-to-noise was achieved at ultralow flow rates for concentration-limited analyses, experiments consuming the same amount of analyte suggest that mass-limited analyses will benefit strongly from the use of low flow rates and avoiding unnecessary sample dilution. By operating under optimal conditions, consumption of just 500 zmol of sample yielded signal-to-noise ratios ~10 for some peptides. These findings have important implications for the analysis of trace biological samples.

Marginean, Ioan; Tang, Keqi; Smith, Richard D.; Kelly, Ryan T.

2014-01-01

103

Characterization of trimethylsilyl derivatives of cerebrosides by direct inlet-chemical ionization mass spectrometry.  

PubMed

Submicrogram quantities of trimethylsilyl derivatives of cerebrosides obtained from the spleen of a patient with Gaucher's disease and from bovine brain were analyzed by direct probe inlet-chemical ionization mass spectrometry, using isobutane as the reagent gas. Quasimolecular ions (QM+, M + 73) and other recognizable fragment ions produced by the successive elimination of trimethylsilanol and sugar residue gave useful information about fatty acid compositions. These ions could also be utilized for qualitative analyses of the molecular species of cerebrosides. Cerebrosides with non-hydroxy and hydroxy fatty acids could be discriminated from each other by comparing the intensities of their quasimolecular ions. Cerebrosides with saturated and monounsaturated fatty acids could also be discrimnated from each other, because the mass number decreased by two mass units in cerebrosides with monounsaturated fatty acids. It was concluded that structural information and molecular species determination could be obtained from small amounts of purified cerebrosides. PMID:650093

Murata, T; Ariga, T; Oshima, M; Miyatake, T

1978-03-01

104

Qualitative Gas Chromatography-Mass Spectrometry Analyses Using Amines as Chemical Ionization Reagent Gases  

NASA Astrophysics Data System (ADS)

Ammonia is a very useful chemical ionization (CI) reagent gas for the qualitative analyses of compounds by positive ion gas chromatography-mass spectrometry (GCMS). The gas is readily available, inexpensive, and leaves no carbon contamination in the MS source. Compounds of interest to our laboratory typically yield abundant protonated or ammoniated species, which are indicative of a compound's molecular weight. Nevertheless, some labile compounds fragment extensively by substitution and elimination reactions and yield no molecular weight information. In these cases, a CI reagent gas mixture of methylamine in methane prepared dynamically was found to be very useful in obtaining molecular weight data. Likewise, deuterated ammonia and deuterated methylamine are useful CI reagent gases for determining the exchangeable protons in organic compounds. Deuterated methylamine CI reagent gas is conveniently prepared by dynamically mixing small amounts of methylamine with excess deuterated ammonia.

Little, James L.; Howard, Adam S.

2013-12-01

105

Water chemical ionization mass spectrometry of aldehydes, ketones esters, and carboxylic acids  

SciTech Connect

Chemical ionization mass spectrometry (CI) of aliphatic and aromatic carbonyl compounds using water as the reagent gas provides intense pseudomolecular ions and class-specific fragmentation patterns that can be used to identify aliphatic aldehydes, ketones, carboxylic acids, and esters. The length of ester acyl and alkyl groups can easily be determined on the basis of loss of alcohols from the protonated parent. Water CI provides for an approximately 200:1 selectivity of carbonyl species over alkanes. No reagent ions are detected above 55 amu, allowing species as small as acetone, propanal, acetic acid, and methyl formate to be identified. When deuterate water was used as the reagent, only the carboxylic acids and ..beta..-diketones showed significant H/D exchange. The use of water CI to identify carbonyl compounds in a wastewater from the supercritical water extraction of lignite coal, in lemon oil, and in whiskey volatiles is discussed.

Hawthorne, S.B.; Miller, D.J.

1986-11-01

106

Atmospheric amines and ammonia measured with a chemical ionization mass spectrometer (CIMS)  

NASA Astrophysics Data System (ADS)

We report measurements of ambient amines and ammonia with a fast response chemical ionization mass spectrometer (CIMS) in a southeastern US forest and a moderately polluted midwestern site during the summer. At the forest site, mostly C3-amines (from pptv to tens of pptv) and ammonia (up to 2 ppbv) were detected, and they both showed temperature dependencies. Aerosol-phase amines measured thermal-desorption chemical ionization mass spectrometer (TDCIMS) showed a higher mass fraction in the evening with cooler temperatures and lower in the afternoon with warmer temperatures, a trend opposite to the gas-phase amines. Concentrations of aerosol-phase primary amines measured with Fourier transform infrared spectroscopy (FTIR) from micron and submicron particles were 2 orders of magnitude higher than the gas-phase amines. These results indicate that gas to particle conversion is one of the major processes that control the ambient amine concentrations at this forest site. Temperature dependencies of C3-amines and ammonia also imply reversible processes of evaporation of these nitrogen-containing compounds from soil surfaces in daytime and deposition to soil surfaces at nighttime. During the transported biomass burning plume events, various amines (C1-C6) appeared at the pptv level, indicating that biomass burning is a substantial source of amines in the southeastern US. At the moderately polluted Kent site, there were higher concentrations of C1- to C6-amines (pptv to tens of pptv) and ammonia (up to 6 ppbv). C1- to C3-amines and ammonia were well correlated with the ambient temperature. C4- to C6-amines showed frequent spikes during the nighttime, suggesting that they were emitted from local sources. These abundant amines and ammonia may in part explain the frequent new particle formation events reported from Kent. Higher amine concentrations measured at the polluted site than at the rural forested site highlight the importance of constraining anthropogenic emission sources of amines.

You, Y.; Kanawade, V. P.; de Gouw, J. A.; Guenther, A. B.; Madronich, S.; Sierra-Hernández, M. R.; Lawler, M.; Smith, J. N.; Takahama, S.; Ruggeri, G.; Koss, A.; Olson, K.; Baumann, K.; Weber, R. J.; Nenes, A.; Guo, H.; Edgerton, E. S.; Porcelli, L.; Brune, W. H.; Goldstein, A. H.; Lee, S.-H.

2014-11-01

107

High-Resolution Hybrid Lithography with Negative Tone Chemically Amplified Resists  

NASA Astrophysics Data System (ADS)

We present in this paper the development of a hybrid lithographic process using negative tone chemically amplified resists. Starting with the Sumitomo commercial negative-tone chemically amplified resist NEB-33, experimental formulations have been developed to extend resolution below 30 nm in electron beam lithography. Thermal and infrared spectroscopy measurements were carried out to determine the macroscopic properties of samples. Electron beam lithography at 50 kV and 100 kV was performed to determine the ultimate resolution. Although they were first designed for electron beam lithography, deep ultra-violet exposures were carried out to develop a hybrid process. Post exposure bake effects on resist line widths and cross-sectional profiles were examined. As a result of process optimization, 20 nm isolated lines have been resolved using these new resists.

Landis, S.; Pauliac, S.; Saint-Pol, J.; Gourgon, C.; Akita, M.; Hanawa, R.; Suetsugu, M.

2004-06-01

108

Soft Ionization of Saturated Hydrocarbons, Alcohols and Nonpolar Compounds by Negative-Ion Direct Analysis in Real-Time Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Large polarizable n-alkanes (approximately C18 and larger), alcohols, and other nonpolar compounds can be detected as negative ions when sample solutions are injected directly into the sampling orifice of the atmospheric pressure interface of the time-of-flight mass spectrometer with the direct analysis in real time (DART) ion source operating in negative-ion mode. The mass spectra are dominated by peaks corresponding to [M + O2]?•. No fragmentation is observed, making this a very soft ionization technique for samples that are otherwise difficult to analyze by DART. Detection limits for cholesterol were determined to be in the low nanogram range.

Cody, Robert B.; Dane, A. John

2013-03-01

109

Volume 209, number 1,2 CHEMICAL PHYSICS LETTERS 25 June 1993 Femtosecond two-photon ionization spectroscopy  

E-print Network

-photon ionization (TPI) spectroscopy [41 and by depletion spectroscopy [ 51. In the case of larger sodium clusters the TPI spectroscopy with nanose- cond lasers fails due to the very short lifetimes (0.33- 3.5 ps;Volume 209, number I,2 CHEMICAL PHYSICS LETTERS 25 June 1993 [12] showed that the TPI spectrum

Kassel, Universität

110

Facilities: NHMFL 9.4 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer Citation: Atmospheric Pressure Laser-Induced Acoustic Desorption Chemical Ionization Mass Spectrometry  

E-print Network

: Atmospheric Pressure Laser-Induced Acoustic Desorption Chemical Ionization Mass Spectrometry for Analysis of atmospheric pressure laser-induced acoustic desorption chemical ionization (AP/ LIAD-CI) source. The laser a powerful new approach for the analysis of saturated hydrocarbon mixtures: atmospheric pressure laser

Weston, Ken

111

Investigation of combwax of honeybees with high-temperature gas chromatography and high-temperature gas chromatography-chemical ionization mass spectrometry. II: High-temperature gas chromatography-chemical ionization mass spectrometry.  

PubMed

Crude combwax of six various honey bee species have been analyzed by high-temperature gas chromatography (HTGC)-chemical ionization mass spectrometry after a two-step silylation procedure. An optimized chromatographic procedure, described previously, enables the separation of high-molecular mass lipid compounds resulting in a characteristic fingerprint of the combwaxes of different honeybee species. The coupling of HTGC to mass spectrometry requires appropriate instrumentation in order to achieve sufficient sensitivity at high elution temperatures and avoid loss of chromatographic resolution. Chemical ionization was carried out using methane as reagent gas in order to determine the molecular mass of the individual compounds by means of abundant quasi molecular ions. To confirm the presence of unsaturated wax esters, ammonia was used as reagent gas. More than 80 lipid constituents were separated and characterized by their mass spectra. Representative chemical ionization mass spectra of individual compounds are presented. Both, HTGC-flame ionization detection data and the results of the HTGC-mass spectrometric investigations enabled a rapid profiling of the individual classes of compounds in crude combwaxes. PMID:10910202

Aichholz, R; Lorbeer, E

2000-06-23

112

Calibrated In Situ Measurement of UT/LS Water Vapor Using Chemical Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Over the past several decades there has been considerable disagreement among in situ water vapor measurements by different instruments at the low part per million (ppm) mixing ratios found in the upper troposphere and lower stratosphere (UT/LS). These discrepancies contribute to uncertainty in our understanding of the microphysics related to cirrus cloud particle nucleation and growth and affect our ability to determine the effect of climate changes on the radiatively important feedback from UT/LS water vapor. To address the discrepancies observed in measured UT/LS water vapor, a new chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor at low mixing ratios. The instrument utilizes a radioactive ? particle source to ionize a flow of sample air drawn into the instrument. A cascade of ion-molecule reactions results in the production of protonated water ions proportional to the water vapor mixing ratio that are then detected by the mass spectrometer. The multi-step nature of the ionization mechanism results in a non-linear sensitivity to water vapor, necessitating calibration across the full range of values to be measured. To accomplish this calibration, we have developed a novel calibration scheme using catalytic oxidation of hydrogen to produce well-defined water vapor mixing ratios that can be introduced into the instrument inlet during flight. The CIMS instrument was deployed for the first time aboard the NASA WB-57 high altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The sensitivity of the instrument to water vapor was calibrated every ~45 minutes in flight from < 1 to 150 ppm. Analysis of in-flight data demonstrates a typical sensitivity of 2000 Hz/ppm at 4.5 ppm with a signal to noise ratio (2 ?) > 50 for a 1 second measurement. The instrument and its calibration system performed successfully in 7 flights during the MACPEX mission, sampling water vapor mixing ratios as low as 4 ppm in stratospheric air. A comparison of the new measurement with other measurements on board the aircraft is expected to help resolve the long-standing differences in low water measurements in the lower stratosphere.

Thornberry, T. D.; Rollins, A.; Gao, R.; Watts, L. A.; Ciciora, S. J.; McLaughlin, R. J.; Fahey, D. W.

2011-12-01

113

Evaluation of ELISA kits followed by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry for the determination of organic pollutants in industrial effluents  

SciTech Connect

Contaminated industrial effluents often contain a variety of organic pollutants which are difficult to analyze by standard GC-MS methods since they often miss the more polar or nonvolatile of these organic compounds. The identification of highly polar analytes by chemical or rapid biological techniques is needed for characterization of the effluents. The present work evaluates the use of enzyme linked immunosorbent assays (ELISA) kits for determining pentachlorophenol, carcinogenic PAHs and BTEX (benzene, toluene, ethylbenzene, and o-, m-, and p-xylene) among the organic analytes present in various industrial effluents from Europe. The analytical protocol applied for the evaluation of the kits was based on the use of ELISA followed by solid-phase extraction (SPE) for the preconcentration of a variety of organic pollutants such as pentachlorophenol, phthalates, and nonylphenol and final determination with LC-MS characterization using an atmospheric pressure chemical ionization (APCI) interface in the positive and negative ionization modes. The developed protocol permitted the unequivocal identification of target analytes such as pentachlorophenol, nonylphenol, dibutylphthalate, dimethylphthalate, bis(2-ethylhexyl)phthalate 2-methylbenzenesulfonamide, and 2,2-dimethylbenzene-sulfonamide present in industrial effluents. The advantages and limitations of the three RaPID-magnetic particle-based ELISA kits applied to the characterization of industrial effluents are also reported.

Castillo, M.; Oubina, A.; Barcelo, D. [CID-CSIC, Barcelona (Spain). Dept. of Environmental Chemistry] [CID-CSIC, Barcelona (Spain). Dept. of Environmental Chemistry

1998-07-15

114

A rapid novel derivatization of amphetamine and methamphetamine using 2,2,2-trichloroethyl chloroformate for gas chromatography electron ionization and chemical ionization mass spectrometric analysis.  

PubMed

Amphetamine and methamphetamine are commonly abused central nervous system stimulants. We describe a rapid new derivatization of amphetamine and methamphetamine using 2,2,2-trichloroethyl chloroformate for gas chromatography-mass spectrometric analysis. Amphetamine and methamphetamine, along with N-propyl amphetamine (internal standard), were extracted from urine using 1-chlorobutane. The derivatization with 2,2,2-trichloroethyl chloroformate can be achieved at room temperature in 10 minutes. The electron ionization mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed two weak molecular ions at m/z 309 and 311, but showed diagnostic strong peaks at m/z 218, 220, and 222. In contrast, chemical ionization of the mass spectrum of amphetamine 2,2,2-trichloroethyl carbamate showed strong (M + 1) ions at m/z 310 and 312 and other strong diagnostic peaks at m/z 274 and 276. The major advantages of this derivative are the presence of a diagnostic cluster of peaks due to the isotopic effect of three chlorine atoms (isotopes 35 and 37) in the derivatized molecule and the relative ease of its preparation. We also observed strong molecular ions for derivatized methamphetamine in the chemical ionization mass spectrum, but the molecular ions were very weak in the electron ionization mass spectrum. We used the scan mode of mass spectrometry in all analyses. When using a urine standard containing 1,000 ng/mL of amphetamine (a 7.4-micromol/L concentration) and methamphetamine (a 6.7-micromol/L concentration), the within-run precisions were 4.8% for amphetamine and 3.6% for methamphetamine. The corresponding between-run precisions were 5.3% for amphetamine and 6.7% for methamphetamine. The assay was linear for amphetamine and methamphetamine concentrations of 250 to 5,000 ng/mL (amphetamine, 1.9-37.0 micromol/L; methamphetamine, 1.7-33.6 micromol/L). The detection limit was 100 ng/mL (amphetamine, 0.74 micromol/L; methamphetamine, 0.67 micromol/L) using the scan mode of electron ionization mass spectrometry. We observed good a correlation between the concentrations of amphetamine and methamphetamine in five urine specimens positive for amphetamines using the more conventional pentafluoropropionyl derivative and our new derivative using 2,2,2-trichloroethyl chloroformate. PMID:9576569

Dasgupta, A; Spies, J

1998-05-01

115

Direct Quantification of Chemical Warfare Agents and Related Compounds at Low ppt Levels: Comparing Active Capillary Dielectric Barrier Discharge Plasma Ionization and Secondary Electrospray Ionization Mass Spectrometry.  

PubMed

A novel active capillary dielectric barrier discharge plasma ionization (DBDI) technique for mass spectrometry is applied to the direct detection of 13 chemical warfare related compounds, including sarin, and compared to secondary electrospray ionization (SESI) in terms of selectivity and sensitivity. The investigated compounds include an intact chemical warfare agent and structurally related molecules, hydrolysis products and/or precursors of highly toxic nerve agents (G-series, V-series, and "new" nerve agents), and blistering and incapacitating warfare agents. Well-defined analyte gas phase concentrations were generated by a pressure-assisted nanospray with consecutive thermal evaporation and dilution. Identification was achieved by selected reaction monitoring (SRM). The most abundant fragment ion intensity of each compound was used for quantification. For DBDI and SESI, absolute gas phase detection limits in the low ppt range (in MS/MS mode) were achieved for all compounds investigated. Although the sensitivity of both methods was comparable, the active capillary DBDI sensitivity was found to be dependent on the applied AC voltage, thus enabling direct tuning of the sensitivity and the in-source fragmentation, which may become a key feature in terms of field applicability. Our findings underline the applicability of DBDI and SESI for the direct, sensitive detection and quantification of several CWA types and their degradation products. Furthermore, they suggest the use of DBDI in combination with hand-held instruments for CWAs on-site monitoring. PMID:25427190

Wolf, Jan-Christoph; Schaer, Martin; Siegenthaler, Peter; Zenobi, Renato

2015-01-01

116

Performance of a corona ion source for measurement of sulfuric acid by chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO3- ions with H2SO4. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (americium-241) ion source which has been used previously. The results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of 1 min it is ~6 × 104 molecule cm-3 of H2SO4. In addition, only a small cross-sensitivity to SO2 has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO2 is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H2SO4 concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H2SO4 is measured by CIMS.

Kürten, A.; Rondo, L.; Ehrhart, S.; Curtius, J.

2011-03-01

117

Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides.  

PubMed

Organic peroxides such as the cumene hydroperoxide I (M(r) = 152 u), the di-tert-butyl peroxide II (M(r) = 146 u) and the tert-butyl peroxybenzoate III (M(r) = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water-methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (< or =50 degrees C) and probe temperature (70-200 degrees C). The mass spectra of these compounds show the formation of (i) an [M + H](+) ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH(3)OH(2)](+) ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH(3)OH(2) (+), i.e. thermochemical parameters (DeltaHdegrees(reaction)) and two kinetic factors such as the capture constant of the initial stable ion-dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster. PMID:14505320

Rondeau, David; Vogel, René; Tabet, Jean-Claude

2003-09-01

118

Document authentication at molecular levels using desorption atmospheric pressure chemical ionization mass spectrometry imaging.  

PubMed

Molecular images of documents were obtained by sequentially scanning the surface of the document using desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS), which was operated in either a gasless, solvent-free or methanol vapor-assisted mode. The decay process of the ink used for handwriting was monitored by following the signal intensities recorded by DAPCI-MS. Handwritings made using four types of inks on four kinds of paper surfaces were tested. By studying the dynamic decay of the inks, DAPCI-MS imaging differentiated a 10-min old from two 4 h old samples. Non-destructive forensic analysis of forged signatures either handwritten or computer-assisted was achieved according to the difference of the contour in DAPCI images, which was attributed to the strength personalized by different writers. Distinction of the order of writing/stamping on documents and detection of illegal printings were accomplished with a spatial resolution of about 140 µm. A Matlab® written program was developed to facilitate the visualization of the similarity between signature images obtained by DAPCI-MS. The experimental results show that DAPCI-MS imaging provides rich information at the molecular level and thus can be used for the reliable document analysis in forensic applications. PMID:24078245

Li, Ming; Jia, Bin; Ding, Liying; Hong, Feng; Ouyang, Yongzhong; Chen, Rui; Zhou, Shumin; Chen, Huanwen; Fang, Xiang

2013-09-01

119

Characterization of prenylated xanthones and flavanones by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Reversed-phase liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) in the positive-ion mode was utilized to analyze crude ether extracts from the root bark of Maclura pomifera, a tree known to have a high content of prenylated xanthones and flavanones. Identification of three xanthones and two flavanones was based on their unique mass spectra. Under optimum conditions peaks corresponding to the [MH](+) ion and characteristic fragments for each compound were observed. (1)H NMR data were used to confirm the identities of two xanthones that had the same molecular mass and similar fragmentation patterns. Fragmentation of the analytes was achieved by application of an electrostatic potential at the entrance of the single quadrupole mass spectrometer. The optimum voltage for fragmentation was found to be related to the class of compounds analyzed and, within each class, to be dependent on the structure of the prenyl moiety. Collision-induced pathways consistent with precedent literature describing the MS characterization of similar compounds and with the observed fragmentation patterns are tentatively proposed. PMID:10797650

da Costa, C T; Dalluge, J J; Welch, M J; Coxon, B; Margolis, S A; Horton, D

2000-04-01

120

A corona discharge atmospheric pressure chemical ionization source with selective NO(+) formation and its application for monoaromatic VOC detection.  

PubMed

We have developed a new type of corona discharge (CD) for atmospheric pressure chemical ionization (APCI) for application in ion mobility spectrometry (IMS) as well as in mass spectrometry (MS). While the other CD-APCI sources are able to generate H3O(+)·(H2O)n as the major reactant ions in N2 or in zero air, the present CD-APCI source has the ability to generate up to 84% NO(+)·(H2O)n reactant ions in zero air. The change of the working gas from zero air to N2 allows us to change the major reactant ions from NO(+)·(H2O)n to H3O(+)·(H2O)n. In this paper we present the description of the new CD-APCI and discuss the processes associated with the NO(+) formation. The selective formation of NO(+)·(H2O)n reactant ions offers chemical ionization based on these ions which can be of great advantage for some classes of chemicals. We demonstrate here a significant increase in the sensitivity of the IMS-MS instrument for monoaromatic volatile organic compound (VOC) detection upon NO(+)·(H2O)n chemical ionization. PMID:24081306

Sabo, Martin; Matej?ík, Štefan

2013-11-21

121

We highlight the selective ionization of acidic components of crude oils and naphthenates by negative-ion electrospray  

E-print Network

We highlight the selective ionization of acidic components of crude oils and naphthenates sample consumption. Angola and offshore Canadian crude oils and Athabasca bitumen were used as supplied differences of acidic species in crude oils and naphthenates and also afford structural characterization

122

Pulsed Chemical Oxygen Iodine Lasers Excited by Pulse Gas Discharge with the Assistance of Surface Sliding Discharge Pre-ionization  

Microsoft Academic Search

Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power. The key point is to obtain a uniform and stable glow discharge in the mixture of singlet delta oxygen and iodide. We propose using an electrode system with the assistance of surface sliding pre-ionization to solve the problem of the stable

Li Guo-Fu; Yu Hai-Jun; Duo Li-Ping; Jin Yu-Qi; Wang Jian; Sang Feng-Ting; Wang De-Zhen

2012-01-01

123

Detection performance of a portable ion mobility spectrometer with 63 Ni radioactive ionization for chemical warfare agents  

Microsoft Academic Search

The detection performance of a portable ion mobility spectrometer (IMS) (SABRE 4000, Smiths Detection) with 63Ni ionization, air purification, and reduced ion mobility measurements using calibrants was investigated for vapors of chemical\\u000a warfare agents. In a matter of several seconds, the SABRE 4000 enabled tentative identification of sarin, soman, cyclohexylsarin,\\u000a tabun, and nitrogen mustard 3, each with a limit of

Shintaro Yamaguchi; Ryuji Asada; Shintaro Kishi; Ryoji Sekioka; Nobuyoshi Kitagawa; Kenichi Tokita; Soichiro Yamamoto; Yasuo Seto

2010-01-01

124

Determination of pharmaceuticals in aqueous samples using positive and negative voltage switching microbore liquid chromatography/electrospray ionization tandem mass spectrometry.  

PubMed

Analytical methods were developed for atorvastatin, novobiocin and roxithromycin using microbore liquid chromatography/electrospray ionization tandem mass spectrometry (microbore LC/ESI-MS/MS) in positive and negative voltage switching mode. Atorvastatin and roxithromycin require the positive-ion mode, whereas the negative-ion mode is required for the determination of novobiocin. Using the positive and negative voltage switching function, the three analytes were determined with one injection, and the time required was half that required using separately run positive- and negative-ion modes, without any reduction in sensitivity. A microbore LC column (100 x 1.0 mm i.d.) was chosen for chromatographic separation with mobile phase solvents acetonitrile and 10 mM aqueous ammonium acetate. The flow-rate was 0.1 ml min(-1) and the injection volume was 1 micro l. The analytes were quantified in the multiple reaction monitoring mode with external standards. By switching the positive and negative voltage, the three analytes were determined with a 4 min chromatographic run and with instrumental detection limits of 1-3 pg. This analytical method, using a microbore LC column combined with solid-phase extraction, was applied successfully to the determination of trace levels of the above pharmaceuticals in aqueous samples. Atorvastatin was detected in a sewage treatment plant final effluent. PMID:12526003

Miao, Xiu-Sheng; Metcalfe, Chris D

2003-01-01

125

Negative electrospray ionization on porous supporting tips for mass spectrometric analysis: electrostatic charging effect on detection sensitivity and its application to explosive detection.  

PubMed

The simplicity and easy manipulation of a porous substrate-based ESI-MS technique have been widely applied to the direct analysis of different types of samples in positive ion mode. However, the study and application of this technique in negative ion mode are sparse. A key challenge could be due to the ease of electrical discharge on supporting tips upon the application of negative voltage. The aim of this study is to investigate the effect of supporting materials, including polyester, polyethylene and wood, on the detection sensitivity of a porous substrate-based negative ESI-MS technique. By using nitrobenzene derivatives and nitrophenol derivatives as the target analytes, it was found that the hydrophobic materials (i.e., polyethylene and polyester) with a higher tendency to accumulate negative charge could enhance the detection sensitivity towards nitrobenzene derivatives via electron-capture ionization; whereas, compounds with electron affinities lower than the cut-off value (1.13 eV) were not detected. Nitrophenol derivatives with pKa smaller than 9.0 could be detected in the form of deprotonated ions; whereas polar materials (i.e., wood), which might undergo competitive deprotonation with the analytes, could suppress the detection sensitivity. With the investigation of the material effects on the detection sensitivity, the porous substrate-based negative ESI-MS method was developed and applied to the direct detection of two commonly encountered explosives in complex samples. PMID:24492411

Wong, Melody Yee-Man; Man, Sin-Heng; Che, Chi-Ming; Lau, Kai-Chung; Ng, Kwan-Ming

2014-03-21

126

Rapid screening procedures for the hydrolysis products of chemical warfare agents using positive and negative ion liquid chromatography–mass spectrometry with atmospheric pressure chemical ionisation  

Microsoft Academic Search

Qualitative screening procedures have been developed for the rapid detection and identification of the hydrolysis products of chemical warfare agents in aqueous samples and extracts, using liquid chromatography–mass spectrometry with positive and negative atmospheric pressure chemical ionisation (APCI). Previously reported screening procedures, which used positive APCI or electrospray ionisation (ESI), were modified by using LC conditions that allowed acquisition of

Robert W Read; Robin M Black

1999-01-01

127

Chemical Characterization of Crude Petroleum Using Nanospray Desorption Electrospray Ionization Coupled with High-Resolution Mass Spectrometry  

SciTech Connect

Nanospray desorption electrospray ionization (nano-DESI) combined with high-resolution mass spectrometry was used for the first time for the analysis of liquid petroleum crude oil samples. The analysis was performed in both positive and negative ionization modes using three solvents one of which (acetonitrile/toluene mixture) is commonly used in petroleomics studies while two other polar solvents (acetonitrile/water and methanol/water mixtures) are generally not compatible with petroleum characterization using mass spectrometry. The results demonstrate that nano-DESI analysis efficiently ionizes petroleum constituents soluble in a particular solvent. When acetonitrile/toluene is used as a solvent, nano-DESI generates electrospray-like spectra. In contrast, strikingly different spectra were obtained using acetonitrile/water and methanol/water. Comparison with the literature data indicates that these solvents selectively extract water-soluble constituents of the crude oil. Water-soluble compounds are predominantly observed as sodium adducts in nano-DESI spectra indicating that addition of sodium to the solvent may be a viable approach for efficient ionization of water-soluble crude oil constituents. Nano-DESI enables rapid screening of different classes of compounds in crude oil samples using solvents that are rarely used for petroleum characterization.

Eckert, Peter A.; Roach, Patrick J.; Laskin, Alexander; Laskin, Julia

2012-02-07

128

Atmospheric amines and ammonia measured with a Chemical Ionization Mass Spectrometer (CIMS)  

NASA Astrophysics Data System (ADS)

We report ambient measurements of amines and ammonia with a~fast response chemical ionization mass spectrometer (CIMS) in a southeastern US forest in Alabama and a~moderately polluted Midwestern site during the summer. In the Alabama forest, mostly C3-amines (from pptv to tens of pptv) and ammonia (up to 2 ppbv) were detected on a daily basis. C3-amines and ammonia showed similar diurnal trends and temperature and wind direction dependences, and were not associated with transported CO and SO2 plumes. Consistent with temperature dependences, amine and ammonia in the gas and aerosol phases showed opposite diurnal trends, indicating gas-to-particle partitioning of amines and ammonia. Temperature dependences also imply reversible processes of amines and ammonia evaporation from soil surfaces in daytime and deposition of amines and ammonia to soil surfaces at nighttime. Various amines (C1-C6) at the pptv level were observed in the transported biomass burning plumes, showing that biomass burning can be a substantial source of amines in the Southeast US. At the moderately polluted Kent site, higher concentrations of amines (C1-C6, from pptv to tens of pptv) and ammonia (up to 6 ppbv) were detected. Diurnal variations of C1- to C3-amines and ammonia were correlated with the ambient temperature. C4- to C6-amines showed abrupt increases during the nighttime, suggesting that they were emitted from local sources. These abundant amines and ammonia may in part explain the frequent new particle formation events reported from Kent. Lower amine concentrations at the rural forested site highlight the importance of constraining anthropogenic sources of amines.

You, Y.; Kanawade, V. P.; de Gouw, J. A.; Guenther, A. B.; Madronich, S.; Sierra-Hernández, M. R.; Lawler, M.; Smith, J. N.; Takahama, S.; Ruggeri, G.; Koss, A.; Olson, K.; Baumann, K.; Weber, R. J.; Nenes, A.; Guo, H.; Edgerton, E. S.; Porcelli, L.; Brune, W. H.; Goldstein, A. H.; Lee, S.-H.

2014-06-01

129

Atmospheric Amines and Ammonia Measured with a Chemical Ionization Mass Spectrometer (CIMS)  

SciTech Connect

We report ambient measurements of amines and ammonia with a fast response chemical ionization mass spectrometer (CIMS) in a Southeastern U.S. forest in Alabama and a moderately polluted Midwestern site during the summer. In the Alabama forest, mostly C3-amines (from pptv to tens of pptv) and ammonia (up to 2 ppbv) were detected on a daily basis. C3-amines and ammonia showed similar diurnal trends and temperature and wind direction dependences, and were not associated with transported CO and SO2 plumes. Consistent with temperature dependences, amine and ammonia in the gas and aerosol phases showed opposite diurnal trends, indicating gas-to-particle partitioning of amines and ammonia. Temperature dependences also imply reversible processes of amines and ammonia evaporation from soil surfaces in daytime and deposition of amines and ammonia to soil surfaces at nighttime. Various amines (C1-C6) at the pptv level were observed in the transported biomass burning plumes, showing that biomass burning can be a substantial source of amines in the Southeast U.S. At the moderately polluted Kent site, higher concentrations of amines (C1-C6, from pptv to tens of pptv) and ammonia (up to 6 ppbv) were detected. Diurnal variations of C1- to C3-amines and ammonia were correlated with the ambient temperature. C4- to C6-amines showed abrupt increases during the nighttime, suggesting that they were emitted from local sources. These abundant amines and ammonia may in part explain the frequent new particle formation events reported from Kent. Lower amine concentrations at the rural forested site highlight the importance of constraining anthropogenic sources of amines.

You, Y.; Kanawade, V. P.; de Gouw, J. A.; Guenther, Alex B.; Madronich, Sasha; Sierra-Hernandez, M. R.; Lawler, M.; Smith, James N.; Takahama, S.; Ruggeri, G.; Koss, A.; Olson, K.; Baumann, K.; Weber, R. J.; Nenes, A.; Guo, H.; Edgerton, Eric S.; Porcelli, L.; Brune, W. H.; Goldstein, Allen H.; Lee, S.-H

2014-11-19

130

Electron-transfer-induced decomposition of 1,2-dioxetanes in negative-mode matrix- assisted laser desorption/ionization time-of-flight mass spectrometry.  

PubMed

1,2-Dioxetanes bearing an aromatic electron donor undergo intramolecular charge-transfer-induced chemiluminescence (CTICL). Although there has been some controversy regarding the mechanisms involved, there is little experimental evidence to strongly support any of the proposed mechanisms. In the course of our investigations, to clarify these mechanisms, we tried to effectively ionize dioxetanes bearing a phenolic group and found that poly(3-octylthiophene-2,5-diyl) was a promising matrix for negative-mode matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS). Electron-transfer ionization was found to take place for dioxetanes bearing a hydroxyphenyl moiety that had been further substituted with an aromatic group, which acted as an antenna to catch an electron from the matrix. Furthermore, the characteristic fragmentation of dioxetanes 3c-3d was thought to occur by the elimination of 2-methyl-1-propene (56 u) and pivalaldehyde (86 u) from deprotonated ion [M - H](-) of dioxetanes, based on the results of muliple mass spectrometry measurements of dioxetanes using MALDI quadrupole ion trap ToF-MS. Based on a comparison of fragmentation in dioxetanes and the corresponding keto esters, dioxetanes were presumed to initially generate excited keto esters from which fragmentation took place. PMID:18401042

Ijuin, Hisako K; Yamada, Masaki; Ohashi, Mamoru; Watanabe, Nobuko; Matsumoto, Masakatsu

2008-01-01

131

Investigation of e-beam sensitive negative-tone chemically amplified resists for binary mask making  

NASA Astrophysics Data System (ADS)

Negative-tone chemically amplified resists MES-EN1G (JSR), FEN-270 (Fujifilm ARCH), EN-024M (TOK) and NEB-22 (Sumitomo) were evaluated for binary mask making. The investigations were performed on an advanced tool set comprising a 50kV e-beam writer Leica SB350, a Steag Hamatech hot/cool plate module APB5000, a Steag Hamatech developer ASP5000, an UNAXIS MASK ETCHER III and a SEM LEO1560 with integrated CD measurement option. We investigated and compared the evaluated resists in terms of resolution, e-beam sensitivity, resist profile, post exposure bake sensitivity, CD-uniformity, line edge roughness, pattern fidelity and etch resistance. Furthermore, the influence of post coating delay and post exposure delay in vacuum and air was determined.

Irmscher, Mathias; Berger, Lothar; Beyer, Dirk; Butschke, Joerg; Dress, Peter; Hoffmann, Thomas; Hudek, Peter; Koepernik, Corinna; Tschinkl, Martin; Voehringer, Peter

2003-08-01

132

A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater  

NASA Astrophysics Data System (ADS)

A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 220 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys.

Saltzman, E. S.; de Bruyn, W. J.; Lawler, M. J.; Marandino, C. A.; McCormick, C. A.

2009-11-01

133

A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater  

NASA Astrophysics Data System (ADS)

A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 170 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys.

Saltzman, E. S.; de Bruyn, W. J.; Lawler, M. J.; Marandino, C. A.; McCormick, C. A.

2009-07-01

134

Identification of milk fat triacylglycerols by capillary supercritical fluid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Identification of milk fat triacylglycerols was accomplished by capillary supercritical fluid chromatography (SFC) combined with atmospheric pressure chemical ionization mass spectrometry [(APCI)MS]. Supercritical carbon dioxide was the carrier fluid in SFC. Ionization was achieved by introducing vapor of ammonia in methanol into the ionization chamber which resulted in the formation of abundant [M + 18]+ and [M - RCCO]+ ions of triaclyglycerols. These ions defined both the molecular weight and the fatty acid constituents of a triacylglycerol, respectively. SFC on a nonpolar stationary phase provided an efficient separation of triacylglycerols according to the combined number of carbon atoms in the acyl chains a molecule. In addition to the identification of the major chromatographic peaks representing molecules with 26-54 acyl carbons, minor peaks representing triacylglycerols with an odd number of acyl carbons were separated and identified. Furthermore, compositional information on partially separated isobaric triacylglycerols, which differed substantially in the chain length of the fatty acyl residues, was achieved within some of the peaks. A new finding of the present study was the formation of abundant [M + 18]+ ions of saturated triacylglycerols in addition to diagnostic fragment ions,being of primary importance in structure elucidation. This extends the applicability of capillary SFC-(APCI)MS in the analysis of both saturated and unsaturated triacylglycerols. PMID:9438239

Laakso, P; Manninen, P

1997-12-01

135

Adhesion-dependent negative friction coefficient on chemically modified graphite at the nanoscale  

NASA Astrophysics Data System (ADS)

From the early tribological studies of Leonardo da Vinci to Amontons’ law, friction has been shown to increase with increasing normal load. This trend continues to hold at the nanoscale, where friction can vary nonlinearly with normal load. Here we present nanoscale friction force microscopy (FFM) experiments for a nanoscale probe tip sliding on a chemically modified graphite surface in an atomic force microscope (AFM). Our results demonstrate that, when adhesion between the AFM tip and surface is enhanced relative to the exfoliation energy of graphite, friction can increase as the load decreases under tip retraction. This leads to the emergence of an effectively negative coefficient of friction in the low-load regime. We show that the magnitude of this coefficient depends on the ratio of tip-sample adhesion to the exfoliation energy of graphite. Through both atomistic- and continuum-based simulations, we attribute this unusual phenomenon to a reversible partial delamination of the topmost atomic layers, which then mimic few- to single-layer graphene. Lifting of these layers with the AFM tip leads to greater deformability of the surface with decreasing applied load. This discovery suggests that the lamellar nature of graphite yields nanoscale tribological properties outside the predictive capacity of existing continuum mechanical models.

Deng, Zhao; Smolyanitsky, Alex; Li, Qunyang; Feng, Xi-Qiao; Cannara, Rachel J.

2012-12-01

136

Optimal choice of pH for toxicity and bioaccumulation studies of ionizing organic chemicals.  

PubMed

It is recognized that the pH of exposure solutions can influence the toxicity and bioaccumulation of ionizing compounds. The present study investigates whether it can be considered a general rule that an ionizable compound is more toxic and more bioaccumulative when in the neutral state. Three processes were identified to explain the behavior of ionizing compounds with changing pH: the change in lipophilicity when a neutral compound becomes ionized, electrical attraction, and the ion trap. The literature was screened for bioaccumulation and toxicity tests of ionizing organic compounds performed at multiple pH levels. Toxicity and bioconcentration factors (BCFs) were higher for acids at lower pH values, whereas the opposite was true for bases. The effect of pH was most pronounced when pH?-?pK(a) was in the range of -1 to 3 for acids, and -3 to 1 for bases. The factor by which toxicity and BCF changed with pH was correlated with the lipophilicity of the compound (log?K(OW) of the neutral compound). For both acids and bases, the correlation was positive, but it was significant only for acids. Because experimental data in the literature were limited, results were supplemented with model simulations using a dynamic flux model based on the Fick-Nernst-Planck diffusion equation known as the cell model. The cell model predicts that bases with delocalized charges may in some cases show declining bioaccumulation with increasing pH. Little information is available for amphoteric and zwitterionic compounds; however, based on simulations with the cell model, it is expected that the highest toxicity and bioaccumulation of these compounds will be found where the compounds are most neutral, at the isoelectric point. PMID:21823161

Rendal, Cecilie; Kusk, Kresten Ole; Trapp, Stefan

2011-11-01

137

Molecular characterization of S- and N-containing organic constituents in ambient aerosols by negative ion mode high-resolution Nanospray Desorption Electrospray Ionization Mass Spectrometry: CalNex 2010 field study  

NASA Astrophysics Data System (ADS)

of ambient aerosols from the 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study were analyzed using negative ion mode Nanospray Desorption Electrospray Ionization High-Resolution Mass Spectrometry (nano-DESI/MS). Four samples per day (6 h each) were collected in Bakersfield, CA on 20-24 June. Four characteristic groups were identified: molecules composed of carbon, hydrogen, and oxygen only (CHO), sulfur- (CHOS), nitrogen- (CHON), and both nitrogen- and sulfur-containing organics (CHONS). The chemical formula and elemental ratios were consistent with the presence of organonitrates, organosulfate, and nitroxy organosulfates in the negative ion mode mass spectra. The number of observed CHO compounds increased in the afternoon samples, suggesting photochemical processing as a source. The average number of CHOS compounds had the smallest changes during the day, consistent with a more broadly distributed source. Both of the nitrogen-containing groups (CHONS and CHON) had greater numbers of compounds in the early morning (midnight to 6 A.M.) and night (6 P.M. to midnight) samples, respectively, consistent with nitrate radical chemistry as a likely source for those compounds. Most of the compounds were found in submicron particles. The size distribution of the number of CHON compounds was bimodal, potentially indicating two types of sources. We conclude that the majority of the compounds observed were secondary in nature with both biogenic and anthropogenic sources. These data are complementary to previous results from positive ion mode nano-DESI/MS analysis of a subset of the same samples providing a more complete view of aerosol chemical composition at Bakersfield.

O'Brien, Rachel E.; Laskin, Alexander; Laskin, Julia; Rubitschun, Caitlin L.; Surratt, Jason D.; Goldstein, Allen H.

2014-11-01

138

Scanning Diode Laser Desorption Thin-Layer Chromatography Coupled with Atmospheric Pressure Chemical Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Continuous wave diode laser is applied for desorption of an analyte from a porous surface of a thin-layer plate covered with a graphite suspension. The thermally desorbed analyte molecules are ionized in the gas phase by a corona discharge at atmospheric pressure. Therefore, both essential processes - the desorption and the ionization of analyte molecules, which are often performed in one step - are separated. Reserpine was chosen as model analyte, which is often used for specification of mass spectrometers. No fragmentation was observed because of efficient collisional cooling under atmospheric pressure. The influence of diode laser power and the composition of the graphite suspension were investigated, and a primary optimization was performed. An interface to allow online qualitative and quantitative full plate detection and analysis of compounds separated by thin-layer chromatography is presented.

Peng, Song; Ahlmann, Norman; Edler, Michael; Franzke, Joachim

139

A field-deployable, chemical ionization time-of-flight mass spectrometer: application to the measurement of gas-phase organic and inorganic acids  

NASA Astrophysics Data System (ADS)

We report a new field-deployable chemical ionization time-of-flight mass spectrometer (CI-TOFMS) for the direct measurement of trace gases in the atmosphere. We apply the technique to the measurement of gas-phase inorganic and organic acids via negative-ion proton transfer, using acetate as the reagent ion. A novel high pressure interface, incorporating two RF-only quadrupoles is used to efficiently focus ions through four stages of differential pumping before analysis with a compact TOFMS. The high ion-duty cycle (>20%) of the TOFMS, coupled to efficient production and transmission of ions in the high pressure interface results in a highly sensitive (>300 ions s-1 pptv-1) instrument capable of the fast measurement of atmospheric gases at trace levels. We demonstrate the efficient transfer and detection of both bare ions and ion-molecule clusters, and characterize the instrument during field measurements aboard the R/V Atlantis as part of the CalNex campaign during the spring of 2010. The in-field short-term precision is better than 5% at 1 pptv (pL/L), for 1-second averages. The detection limit (3?, 1-second averages) of the current version of the CI-TOFMS, as applied to the in situ detection of gas-phase acids, is limited by the magnitude and variability in the background determination and was determined to be 4 pptv.

Bertram, T. H.; Kimmel, J. R.; Crisp, T. A.; Ryder, O. S.; Yatavelli, R. L. N.; Thornton, J. A.; Cubison, M. J.; Gonin, M.; Worsnop, D. R.

2011-03-01

140

Facilities: NHMFL 9.4 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometer Citation: Characterization of Pine Pellet and Peanut Hull Pyrolysis of Bio-Oils by Negative-Ion Electrospray Ionization Fourier  

E-print Network

: Characterization of Pine Pellet and Peanut Hull Pyrolysis of Bio-Oils by Negative-Ion Electrospray Ionization pine pellets and peanut hulls, generates a hydrocarbon-rich liquid product (bio-oil) consisting of oily solubility. Peanut hull bio-oil is much more compositionally complex and contains more nitrogen

Weston, Ken

141

Measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry during the 2009 SHARP field campaign  

NASA Astrophysics Data System (ADS)

We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry (ID-CIMS). HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. During the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) Field Campaign, HONO measurements were continuously conducted from 1 May to 1 June at a site located on the campus of the University of Houston. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise. The nighttime HONO peaks show close correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry likely contributes to HONO formation. A higher nighttime HONO peak concentration typically precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration. Because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

Levy, Misti; Zhang, Renyi; Zheng, Jun; Zhang, Annie L.; Xu, Wen; Gomez-Hernandez, Mario; Wang, Yuan; Olaguer, Eduardo

2014-09-01

142

Pulsed Chemical Oxygen Iodine Lasers Excited by Pulse Gas Discharge with the Assistance of Surface Sliding Discharge Pre-ionization  

NASA Astrophysics Data System (ADS)

Continuous-wave chemical oxygen-iodine lasers (COILs) can be operated in a pulsed operation mode to obtain a higher peak power. The key point is to obtain a uniform and stable glow discharge in the mixture of singlet delta oxygen and iodide. We propose using an electrode system with the assistance of surface sliding pre-ionization to solve the problem of the stable glow discharge with a large aperture. The pre-ionization unit is symmetrically fixed on the plane of the cathode surface. A uniform and stable glow discharge is obtained in a mixture of iodide (such as CH3I) and nitrogen at the specific deposition energy of 4.5 J/L, pressure of 1.99-3.32 kPa, aperture size of 11 cm × 10 cm. The electrode system is applied in a pulsed COIL. Laser energy up to 4.4 J is obtained and the specific energy output is 2 J/L.

Li, Guo-Fu; Yu, Hai-Jun; Duo, Li-Ping; Jin, Yu-Qi; Wang, Jian; Sang, Feng-Ting; Wang, De-Zhen

2012-05-01

143

Stability of plasma gamma-hydroxybutyrate determined by gas chromatography-positive ion chemical ionization-mass spectrometry.  

PubMed

An effective method for the determination of gamma-hydroxybutyric acid (GHB) in human plasma is described that utilizes a simple liquid-liquid extraction procedure and gas chromatography-positive ion chemical ionization-mass spectrometry (GC-PCI-MS). The method has been used to study the stability of plasma GHB under several storage conditions. Following the extraction with acetonitrile, GHB and deuterated GHB (GHB-d(6)) were derivatized with N,O-bis[trimethylsilyl] trifluoroacetamide (BSFTA). After the separation on a capillary GC column, the derivatives were ionized with ammonia reagent gas and analyzed by MS. The lower limit of quantitation in 100 microL of plasma was 2.5 microg/mL, over a range from 2.5 to 250 microg/mL. The coefficients of variation did not exceed 3.9% and the mean measured concentrations did not deviate more than 8% from the target for both intra- and interassay precision and accuracy. Plasma GHB was found to be stable at -20 degrees C for up to 9 months, at room temperature for 48 h, and after 3 freeze/thaw cycles. It was also found to be stable in processed samples stored at room temperature for 5 days and for 15 days at -20 degrees C. PMID:14606997

Chen, Meng; Andrenyak, David M; Moody, David E; Foltz, Rodger L

2003-10-01

144

Analysis of toxic norditerpenoid alkaloids in Delphinium species by electrospray, atmospheric pressure chemical ionization, and sequential tandem mass spectrometry.  

PubMed

A rapid electrospray mass spectrometry method was developed for screening larkspur (Delphinium spp.) plant material for toxic norditerpenoid alkaloids. The method was calibrated using two standard alkaloids, methyllycaconitine (1) and deltaline (2), with a recovery of 92% from spiked samples and relative standard deviations of 6.0% and 8.1% for the two alkaloids, respectively. Thirty-three samples of plains larkspur, Delphinium geyeri, were analyzed. Methyllycaconitine (1) concentration was 0.27% +/- 0.08% during a 1-month period in 1997 establishing the relative risk of poisoning from the plant to be low. The method was also applied to the trace analysis (<1 ppm) of 1 in serum samples from sheep dosed different levels of the alkaloid. Electrospray ionization combined with sequential tandem mass spectrometry and HPLC coupled to atmospheric pressure chemical ionization (APCI) mass spectrometry were used to detect and tentatively identify three new norditerpenoid alkaloids from Delphinium nuttallianum [bearline (6), 14-acetylbearline (7), 16-deacetylgeyerline (8)]. The tentative structure of the new alkaloids was predicted from the tandem mass spectra fragmentation patterns and assigning the substitution pattern for methoxy and acetyl groups at the C-14 and C-16 carbons. PMID:10606571

Gardner, D R; Panter, K E; Pfister, J A; Knight, A P

1999-12-01

145

Early time evolution of negative ion clouds and electron density depletions produced during electron attachment chemical release experiments  

NASA Technical Reports Server (NTRS)

Two-dimensional electrostatic particle-in-cell simulations are used to study the early time evolution of electron depletions and negative ion clouds produced during electron attachment chemical releases in the ionosphere. The simulation model considers the evolution in the plane perpendicular to the magnetic field and a three-species plasma that contains electrons, positive ions, and also heavy negative ions that result as a by-product of the electron attachment reaction. The early time evolution (less than the negative ion cyclotron period) of the system shows that a negative charge surplus initially develops outside of the depletion boundary as the heavy negative ions move across the boundary. The electrons are initially restricted from moving into the depletion due to the magnetic field. An inhomogenous electric field develops across the boundary layer due to this charge separation. A highly sheared electron flow velocity develops in the depletion boundary due to E x B and Delta-N x B drifts that result from electron density gradients and this inhomogenous electric field. Structure eventually develops in the depletion boundary layer due to low-frequency electrostatic waves that have growth times shorter than the negative ion cyclotron period. It is proposed that these waves are most likely produced by the electron-ion hybrid instability that results from sufficiently large shears in the electron flow velocity.

Scales, W. A.; Bernhardt, P. A.; Ganguli, G.

1994-01-01

146

Extracting chemical potentials of quarks from ratios of negatively/positively charged particles in high-energy collisions  

NASA Astrophysics Data System (ADS)

The transverse momentum spectrums of ? -, ? +, K -, K +, , and p produced in p-Pb collisions at TeV measured by the CMS Collaboration and in Pb-Pb collisions at TeV measured by the ALICE Collaboration are described by the Tsallis distribution. Then, the ratios of negatively/positively charged particles are obtained. The chemical potentials of u-quark, d-quark, s-quark, baryon number, isospin, and strangeness are obtained by using different configurations of the ratios. Comparing with the masses of final-state particles, all the six types of chemical potentials are small.

Liu, Fu-Hu; Tian, Tian; Zhao, Hong; Li, Bao-Chun

2014-03-01

147

Investigation of the unusual behavior of metolachlor under chemical ionization in a hybrid 3D ion trap mass spectrometer.  

PubMed

This article describes the strange behavior of the widely used herbicide metolachlor under chemical ionization conditions in a hybrid source ion trap mass spectrometer in gas chromatography/mass spectrometry (GC/MS) coupling. With the use of ammonia as the reagent gas, metolachlor provides a chlorinated ion at m/z 295/297, almost as abundant as the protonated molecule at m/z 284/286, which cannot be isolated to perform tandem mass spectrometry (MS(n)) experiments. Curiously, this ion at m/z = M + 12 is not observed for the herbicides acetochlor and alachlor, which present very similar chemical structures. The chemical structure of the m/z 295/297 ions and the explanation of the observed phenomenon based on the metastable behavior of these ions were elucidated on the basis of experiments including isotopic labeling and modifications of the operating conditions of the ion trap mass spectrometer. This work allows one to give new recommendations for an optimized use of hybrid source ion trap mass spectrometers. PMID:21923170

Goulden, Pierre Henri; Coffinet, Sarah; Genty, Christophe; Bourcier, Sophie; Sablier, Michel; Bouchonnet, Stéphane

2011-10-15

148

Molecular characterization of cancer reveals interactions between ionizing radiation and chemicals on rat mammary carcinogenesis.  

PubMed

Although various mechanisms have been inferred for combinatorial actions of multiple carcinogens, these mechanisms have not been well demonstrated in experimental carcinogenesis models. We evaluated mammary carcinogenesis initiated by combined exposure to various doses of radiation and chemical carcinogens. Female rats at 7 weeks of age were ?-irradiated (0.2-2 Gy) and/or exposed to 1-methyl-1-nitrosourea (MNU) (20 or 40 mg/kg, single intraperitoneal injection) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (40 mg/kg/day by gavage for 10 days) and were observed until 50 weeks of age. The incidence of mammary carcinoma increased steadily as a function of radiation dose in the absence of chemicals; mathematical analysis supported an additive increase when radiation was combined with a chemical carcinogen, irrespective of the chemical species and its dose. Hras mutations were characteristic of carcinomas that developed after chemical carcinogen treatments and were overrepresented in carcinomas induced by the combination of radiation and MNU (but not PhIP), indicating an interaction of radiation and MNU at the level of initiation. The expression profiles of seven classifier genes, previously shown to distinguish two classes of rat mammary carcinomas, categorized almost all examined carcinomas that developed after individual or combined treatments with radiation (1 Gy) and chemicals as belonging to a single class; more comprehensive screening using microarrays and a separate test sample set failed to identify differences in gene expression profiles among these carcinomas. These results suggest that a complex, multilevel interaction underlies the combinatorial action of radiation and chemical carcinogens in the experimental model. PMID:24105445

Imaoka, Tatsuhiko; Nishimura, Mayumi; Doi, Kazutaka; Tani, Shusuke; Ishikawa, Ken-ichi; Yamashita, Satoshi; Ushijima, Toshikazu; Imai, Takashi; Shimada, Yoshiya

2014-04-01

149

Rapid characterization of chemical compounds in liquid and solid states using thermal desorption electrospray ionization mass spectrometry.  

PubMed

Rapid characterization of thermally stable chemical compounds in solid or liquid states is achieved through thermal desorption electrospray ionization mass spectrometry (TD-ESI/MS). A feature of this technique is that sampling, desorption, ionization, and mass spectrometric detection are four separate events with respect to time and location. A metal probe was used to sample analytes in their solid or liquid states. The probe was then inserted in a preheated oven to thermally desorb the analytes on the probe. The desorbed analytes were carried by a nitrogen gas stream into an ESI plume, where analyte ions were formed via interactions with charged solvent species generated in the ESI plume. The analyte ions were subsequently detected by a mass analyzer attached to the TD-ESI source. Quantification of acetaminophen in aqueous solutions using TD-ESI/MS was also performed in which a linear response for acetaminophen was obtained between 25 and 500 ppb (R(2) = 0.9978). The standard deviation for a reproducibility test for ten liquid samples was 9.6%. Since sample preparation for TD-ESI/MS is unnecessary, a typical analysis can be completed in less than 10 s. Analytes such as the active ingredients in over-the-counter drugs were rapidly characterized regardless of the different physical properties of said drugs, which included liquid eye drops, viscous cold syrup solution, ointment cream, and a drug tablet. This approach was also used to detect trace chemical compounds in illicit drugs and explosives, in which samples were obtained from the surfaces of a cell phone, piece of luggage made from hard plastic, business card, and wooden desk. PMID:24050317

Huang, Min-Zong; Zhou, Chi-Chang; Liu, De-Lin; Jhang, Siou-Sian; Cheng, Sy-Chyi; Shiea, Jentaie

2013-10-01

150

Chemical Analysis of Complex Organic Mixtures Using Reactive Nanospray Desorption Electrospray Ionization Mass Spectrometry  

SciTech Connect

Reactive nanospray desorption electrospray ionization (nano-DESI) combined with high-resolution mass spectrometry was utilized for the analysis of secondary organic aerosol produced through ozonolysis of limonene (LSOA). Previous studies showed that LSOA constituents are multifunctional compounds containing aldehyde and ketone groups. In this study, we used the selectivity of the Girard T (GT) reagent towards carbonyl compounds to examine the utility of reactive nano-DESI for the analysis of complex organic mixtures. In these experiments, 1-100 {micro}M GT solution was used as a working solvent for reactive nano-DESI analysis. Abundant products of a single addition of GT to LSOA constituents were observed at GT concentrations in excess of 10 {micro}M. We found that LSOA compounds with 18-20 carbon atoms (dimers) and 27-30 carbon atoms (trimers) react with GT through a simple addition reaction resulting in formation of the carbinolamine derivative. In contrast, reactions of GT with monomeric species result in formation of both the carbinolamine and the hydrazone derivatives. In addition, several monomers did not react with GT on the timescale of our experiment. These molecules were characterized by relatively high values of the double bond equivalent (DBE) and low oxygen content. Furthermore, because addition of a charged GT tag to a neutral molecule eliminates the discrimination against the low proton affinity compounds in the ionization process, reactive nano-DESI analysis enables quantification of individual compounds in the complex mixture. For example, we were able to estimate for the first time the amounts of dimers and trimers in the LSOA mixture. Specifically, we found that the most abundant LSOA dimer was detected at ca. 0.5 pg level and the total amount of dimers and trimers in the analyzed sample was just around 11 pg. Our results indicate that reactive nano-DESI is a valuable approach for examining the presence of specific functional groups and quantification of compounds possessing these groups in complex mixtures.

Laskin, Julia; Eckert, Peter A.; Roach, Patrick J.; Heath, Brandi S.; Nizkorodov, Sergey A.; Laskin, Alexander

2012-08-21

151

Accurate mass measurements and ultrahigh-resolution: evaluation of different mass spectrometers for daily routine analysis of small molecules in negative electrospray ionization mode.  

PubMed

Six mass spectrometers based on different mass analyzer technologies, such as time-of-flight (TOF), hybrid quadrupole-TOF (Q-TOF), orbitrap, Fourier transform ion cyclotron resonance (FT-ICR), and triple quadrupole (QqQ), installed at independent laboratories have been tested during a single day of work for the analysis of small molecules in negative electrospray ionization (ESI) mode. The uncertainty in the mass measurements obtained from each mass spectrometer has been determined by taking the precision and accuracy of replicate measurements into account. The present study is focused on calibration processes (before, after, and during the mass measurement), the resolving power of the mass spectrometers, and the data processing for obtaining elemental formulae. The mass range between m/z 100 and 600 has been evaluated with a mix of four standards. This mass range includes small molecules usually detected in food and environmental samples. Negative ESI has been tested as there is almost no data on accurate mass (AM) measurements in this mode. Moreover, it has been used because it is the ESI mode for analysis of many compounds, such as pharmaceutical, herbicides, and fluorinated compounds. Natural organic matter has been used to demonstrate the significance of ultrahigh-resolution in complex mixtures. Sub-millidalton accuracy and precision have been obtained with Q-TOF, FT-ICR, and orbitrap achieving equivalent results. Poorer accuracy and precision have been obtained with the QqQ used: 11 mDa root-mean-square error and 6-11 mDa standard deviation. Some advice and requirements for daily AM routine analysis are also discussed here. PMID:21553215

Cortés-Francisco, Nuria; Flores, Cintia; Moyano, Encarnación; Caixach, Josep

2011-07-01

152

Simultaneous detection of polar and nonpolar compounds by ambient mass spectrometry with a dual electrospray and atmospheric pressure chemical ionization source.  

PubMed

A dual ionization source combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) was developed to simultaneously ionize both polar and nonpolar compounds. The source was constructed by inserting a fused silica capillary into a stainless steel column enclosed in a glass tube. A high dc voltage was applied to a methanol solution flowing in the fused silica capillary to generate an ESI plume at the capillary tip. A high ac voltage was applied to a ring electrode attached to the glass tube to generate plasma from the nitrogen gas flowing between the glass tube and the stainless steel column. The concentric arrangement of the ESI plume and the APCI plasma in the source ensured that analytes entering the ionization region interacted with both ESI and APCI primary ion species generated in the source. Because the high voltages required for ESI and APCI were independently applied and controlled, the dual ion source could be operated in ESI-only, APCI-only, or ESI+APCI modes. Analytes were introduced into the ESI and/or APCI plumes by irradiating sample surfaces with a continuous-wavelength laser or a pulsed laser beam. Analyte ions could also be produced by directing the dual ESI+APCI source toward sample surfaces for desorption and ionization. The ionization mechanisms involved in the dual ion source include Penning ionization, ion molecule reactions, and fused-droplet electrospray ionization. Standards of polycyclic aromatic hydrocarbons, angiotensin I, lidocaine, ferrocene, diesel, and rosemary oils were used for testing. Protonated analyte ions were detected in ESI-only mode, radical cations were detected in APCI-only mode, and both types of ions were detected in ESI+APCI mode. PMID:25562530

Cheng, Sy-Chyi; Jhang, Siou-Sian; Huang, Min-Zong; Shiea, Jentaie

2015-02-01

153

Analysis of intact tetraether lipids in archaeal cell material and sediments by high performance liquid chromatography\\/atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

A method combining normal phase high performance liquid chromatography (HPLC) with positive ion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was developed for the analysis of intact glycerol dialkyl glycerol tetraethers (GDGTs) in archaeal cell material and sediments. All GDGTs previously reported to occur in the thermophilic archaeon Sulfolobus solfataricus could be identified based on their mass spectra and retention

J. S. Sinninghe Damsté; E. C. Hopmans; S. Schouten; R. D. Pancost; M. T. J. van der Meer

2000-01-01

154

Chemically Etched Open Tubular and Monolithic Emitters for Nanoelectrospray Ionization Mass Spectrometry  

PubMed Central

We have developed a new procedure for fabricating fused silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior. Surface tension causes the etchant to climb the capillary exterior, and the etch rate in the resulting meniscus decreases as a function of distance from the bulk solution. Etching continues until the silica touching the hydrofluoric acid reservoir is completely removed, essentially stopping the etch process. The resulting emitters have no internal taper, making them much less prone to clogging compared to e.g. pulled emitters. The high aspect ratios and extremely thin walls at the orifice facilitate very low flow rate operation; stable ESI-MS signals were obtained for model analytes from 5-?m-diameter emitters at a flow rate of 5 nL/min with a high degree of inter-emitter reproducibility. In extensive evaluation, the etched emitters were found to enable approximately four times as many LC-MS analyses of proteomic samples before failing compared with conventional pulled emitters. The fabrication procedure was also employed to taper the ends of polymer monolith-containing silica capillaries for use as ESI emitters. In contrast to previous work, the monolithic material protrudes beyond the fused silica capillaries, improving the monolith-assisted electrospray process. PMID:17105173

Kelly, Ryan T.; Page, Jason S.; Luo, Quanzhou; Moore, Ronald J.; Orton, Daniel J.; Tang, Keqi; Smith, Richard D.

2007-01-01

155

Chemical Analysis of Organic Aerosols Using Reactive Nanospray Desorption Electrospray Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Nanospray Desorption Electrospray Ionization (nano-DESI) technique integrated with high resolution mass spectrometry (HR-MS) enables molecular level analysis of organic aerosol (OA) samples. In nano-DESI, analyte is desorbed into a small volume solvent bridge formed between two capillaries positioned in contact with analyte and enables fast and efficient characterization of OA collected on substrates without sample preparation. We report applications of the nano-DESI/HR-MS approach in a number of our recent studies focused on molecular identification of organic compounds in laboratory and in field collected OA samples. Reactive nano-DESI approach where selected reagent is added to the solvent is used for examining the presence of individual species containing specific functional groups and for their quantification within complex mixtures of OA. Specifically, we use the Girard's reagent T (GT) to probe and quantify carbonyl compounds in the SOA mixtures. We estimate for the first time the amounts of dimers and trimers in the SOA mixtures. We found that the most abundant dimer in limonene/O3 SOA was detected at the ˜0.5 pg level and the total amount of dimers and trimers in the analyzed sample was ˜11 pg. Understanding of the OA composition at the molecular level allowed us to identify key aging reactions, including the transformation of carbonyls to imines and carbonyl-imine oligomerization, that may contribute to the formation of brown carbon in the atmosphere.

Laskin, A.; Laskin, J.; Nizkorodov, S.

2013-12-01

156

Chemical chaperones reduce ionizing radiation-induced endoplasmic reticulum stress and cell death in IEC-6 cells.  

PubMed

Radiotherapy, which is one of the most effective approaches to the treatment of various cancers, plays an important role in malignant cell eradication in the pelvic area and abdomen. However, it also generates some degree of intestinal injury. Apoptosis in the intestinal epithelium is the primary pathological factor that initiates radiation-induced intestinal injury, but the mechanism by which ionizing radiation (IR) induces apoptosis in the intestinal epithelium is not clearly understood. Recently, IR has been shown to induce endoplasmic reticulum (ER) stress, thereby activating the unfolded protein response (UPR) signaling pathway in intestinal epithelial cells. However, the consequences of the IR-induced activation of the UPR signaling pathway on radiosensitivity in intestinal epithelial cells remain to be determined. In this study, we investigated the role of ER stress responses in IR-induced intestinal epithelial cell death. We show that chemical ER stress inducers, such as tunicamycin or thapsigargin, enhanced IR-induced caspase 3 activation and DNA fragmentation in intestinal epithelial cells. Knockdown of Xbp1 or Atf6 with small interfering RNA inhibited IR-induced caspase 3 activation. Treatment with chemical chaperones prevented ER stress and subsequent apoptosis in IR-exposed intestinal epithelial cells. Our results suggest a pro-apoptotic role of ER stress in IR-exposed intestinal epithelial cells. Furthermore, inhibiting ER stress may be an effective strategy to prevent IR-induced intestinal injury. PMID:24973711

Lee, Eun Sang; Lee, Hae-June; Lee, Yoon-Jin; Jeong, Jae-Hoon; Kang, Seongman; Lim, Young-Bin

2014-07-25

157

Measurement of atmospheric amines and ammonia using the high resolution time-of-flight chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Ammonia (NH3) and amines play important roles in the nucleation and growth of atmospheric aerosols. To identify the sources of these chemicals in the densely populated and industrialized Yangtze River Delta region of China, we conducted measurements of NH3 and several amines, including methylamine (CH3NH2), C2-amines (C2H7N), and C3-amines (C3H9N) at a suburban site of Nanjing, China, during summer 2012. Using a high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS, Aerodyne), 1-min-averaged concentrations of NH3 and amines ranged from a few parts per trillions by volume (pptv) to dozens of parts per billion by volume (ppbv). The average ± 1? concentrations of NH3 and total amines during the measurement period were 1.7 ± 2.3 ppbv and 7.2 ± 7.4 pptv, respectively. Among the amines, C2-amines were the most abundant, accounting for 54% of the total amine loading. Significant correlations between NH3 and all three types of amines (0.65 < r2 < 0.80) indicate similar emission sources. Analysis of meteorological conditions indicated that these NH3 and amine laden air masses mainly originated from nearby industrial areas where NH3 was used for selective catalytic reduction of nitrogen oxides (NOx). The results of this work indicate that industrial emissions in Nanjing, China may have a significant impact on local and regional aerosol chemistry by supplying considerable amount of amines.

Zheng, Jun; Ma, Yan; Chen, Mindong; Zhang, Qi; Wang, Lin; Khalizov, Alexei F.; Yao, Lei; Wang, Zhen; Wang, Xing; Chen, Linxi

2015-02-01

158

Determination of hydroxylated metabolites of polycyclic aromatic hydrocarbons in human hair by gas chromatography–negative chemical ionization mass spectrometry  

Microsoft Academic Search

The study describes the determination of mono-hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs), metabolites of PAHs, in human hair. Twelve selected OH-PAHs from two to four rings, generally determined in urine analysis, were investigated as markers of human exposure to PAHs. Following hydrolysis of hair specimens of 50–300mg with 1M NaOH, OH-PAHs were extracted using dichloromethane and submitted to an optimized derivatization

Claude Schummer; Brice M. R. Appenzeller; Maurice Millet; Robert Wennig

2009-01-01

159

Measurements of Nitrous Acid (HONO) Using Ion Drift - Chemical Ionization Mass Spectrometry during the 2009 SHARP Field Campaign  

NASA Astrophysics Data System (ADS)

During the 2009 SHARP Field Campaign in Houston, TX, measurements of HONO were continuously conducted from May 1 to June 1 at a site located on the campus of the University of Houston. We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift - chemical ionization mass spectrometry (ID-CIMS). In our innovative method, HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. In this presentation, we will discuss the temporal trends and sources of HONO, as well as, as the involvement of HONO in the formation of key atmospheric constituents, such as ozone. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise; the averaged daytime and nighttime concentrations are 0.15 × 0.05 and 0.26 × 0.04, respectively. The nighttime measured HONO peaks show strong correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry represents a significant contributor to the HONO yield. A higher nighttime HONO peak concentration consistently precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration do. Using a kinetic approach, we estimate an uptake coefficient in the range of 6 x 10-4 to 2 x 10-3 for the heterogeneous conversion of NO2 to HONO on aerosol surfaces, which is necessary to account for the measured nighttime HONO peaks. Our results underscore the importance of aerosol heterogeneous chemistry in HONO production and the contributions of this non-photolytic HONO source to the radical budget and the photochemical ozone production in this region. Furthermore, because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

Levy, M. E.; Zhang, R.

2013-12-01

160

Identification of Coagulase-Negative Staphylococci from Bovine Intramammary Infection by Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry  

PubMed Central

Coagulase-negative staphylococci (CoNS) are among the main pathogens causing bovine intramammary infection (IMI) in many countries. However, one of the limitations related to the specific diagnosis of CoNS is the lack of an accurate, rapid, and convenient method that can differentiate the bacterial species comprising this group. The aim of this study was to evaluate the ability of matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) to accurately identify CoNS species in dairy cow IMI. In addition, the study aimed to determine the frequency of CoNS species causing bovine IMI. A total of 108 bacterial isolates were diagnosed as CoNS by microbiological cultures from two milk samples collected from 21 dairy herds; the first sample was collected at the cow level (i.e., 1,242 composite samples from all quarters), while the second sample was collected at the mammary quarter level (i.e., 1,140 mammary samples collected from 285 cows). After CoNS isolation was confirmed by microbiological culture for both samples, all CoNS isolates (n = 108) were genotypically differentiated by PCR restriction fragment length polymorphism (RFLP) analysis of a partial groEL gene sequence and subjected to the MALDI-TOF MS identification procedure. MALDI-TOF MS correctly identified 103 (95.4%) of the CoNS isolates identified by PCR-RFLP at the species level. Eleven CoNS species isolated from bovine IMI were identified by PCR-RFLP, and the most prevalent species was Staphylococcus chromogenes (n = 80; 74.1%). In conclusion, MALDI-TOF MS may be a reliable alternative method for differentiating CoNS species causing bovine IMI. PMID:24622096

Gonçalves, Juliano Leonel; Barreiro, Juliana Regina; Braga, Patrícia Aparecida de Campos; Prada e Silva, Luis Felipe; Eberlin, Marcos Nogueira

2014-01-01

161

A validated UPLC-MS/MS assay using negative ionization mode for high-throughput determination of pomalidomide in rat plasma.  

PubMed

In this study, a sensitive UPLC-MS/MS assay was developed and validated for high-throughput determination of pomalidomide in rat plasma using celecoxib as an internal standard (IS). Liquid liquid extraction using dichloromethane was employed to extract pomalidomide and IS from 200?L of plasma. Chromatographic separation was carried on Acquity BEH™ C18 column (50mm×2.1mm, 1.7?m) using an isocratic mobile phase of acetonitrile: 10mM ammonium acetate (80:20, v/v), at a flow rate of 0.250mL/min. Both pomalidomide and IS were eluted at 0.66±0.03 and 0.80±0.03min, respectively, with a total run time of 1.5min only. A triple quadruple tandem mass spectrometer using electrospray ionization in negative mode was employed for analyte detection. The precursor to product ion transitions of m/z 272.01?160.89 for pomalidomide and m/z 380.08?316.01 for IS were used to quantify them respectively, multiple reaction monitoring mode. The developed method was validated according to regulatory guideline for bioanalytical method validation. The linearity in plasma sample was achieved in the concentration range of 0.47-400ng/mL (r(2)?0.997). The intra and inter-day precision values were ?11.1% (RSD, %) whereas accuracy values ranged from -6.8 to 8.5% (RE, %). In addition, other validation results were within the acceptance criteria and the method was successfully applied in a pharmacokinetic study of pomalidomide in rats. PMID:25621435

Iqbal, Muzaffar; Ezzeldin, Essam; Al-Rashood, Khalid A; Shakeel, Faiyaz

2015-03-01

162

Determination of the enantiomer fraction of PBB 149 by gas chromatography/electron capture negative ionization tandem mass spectrometry in the selected reaction monitoring mode.  

PubMed

Enantioselective determination of the atropisomers of 2,2',3,4',5',6-hexabromobiphenyl (PBB 149) in a purified sample from a bird egg was attempted in this work. By application of the classic method for PBB determination, i.e. gas chromatography coupled to electron capture negative ionization mass spectrometry (GC/ECNI-MS) using the bromide ions, the enantiomers interfered with another brominated compound. Subsequent measurements clarified that this interference did not occur in the mass chromatogram of the molecular ion of PBB 149. Therefore, a GC/ECNI tandem mass spectrometry (MS/MS) method was developed, based on the fragmentation of [M]-. A suitable precursor-product ion transition was found for m/z 627.5 --> 80 +/- 1.5, representing the most abundant ion trace of the molecular ion and the bromide ions. Optimization of the ion source temperature, the methane gas pressure, and the collision voltages resulted in a robust method that could solve the problem. Subsequent injections of a technical PBB product (Firemaster BP-6) resulted in the anticipated racemic proportion (enantiomer fraction (EF) = 0.50 +/- 0.02 (n = 8)). By contrast, the EF in the purified extract of a bird egg was found to be 0.42 +/- 0.02 (n = 10), indicative of a significant enantioenrichment of the second eluting atropisomer. Additional measurements were performed on a non-chiral column. These measurements allowed for the detection of 16 hexabromobiphenyls (hexa-BBs) in Firemaster BP-6. These comparisons verified that PBB 149 enantiomers did not interfere with an isomer that could falsify the enantiomer fraction in the sample. The novel method using GC/ECNI-MS/MS in the selected reaction monitoring (SRM) mode was eight times more sensitive than application of conventional GC/ECNI-MS selected ion monitoring (SIM) analysis of the molecular ion. PMID:16302204

von der Recke, Roland; Mariussen, Espen; Berger, Urs; Götsch, Arntraut; Herzke, Dorte; Vetter, Walter

2005-01-01

163

Analysis of chemical warfare agents in food products by atmospheric pressure ionization-high field asymmetric waveform ion mobility spectrometry-mass spectrometry.  

PubMed

Flow injection high field asymmetric waveform ion mobility spectrometry (FAIMS)-mass spectrometry (MS) methodology was developed for the detection and identification of chemical warfare (CW) agents in spiked food products. The CW agents, soman (GD), sarin (GB), tabun (GA), cyclohexyl sarin (GF), and four hydrolysis products, ethylphosphonic acid (EPA), methylphosphonic acid (MPA), pinacolyl methylphosphonic acid (Pin MPA), and isopropyl methylphosphonic acid (IMPA) were separated and detected by positive ion and negative ion atmospheric pressure ionization-FAIMS-MS. Under optimized conditions, the compensation voltages were 7.2 V for GD, 8.0 V for GA, 7.2 V for GF, 7.6 V for GB, 18.2 V for EPA, 25.9 V for MPA, -1.9 V for PinMPA, and +6.8 V for IMPA. Sample preparation was kept to a minimum, resulting in analysis times of 3 min or less per sample. The developed methodology was evaluated by spiking bottled water, canola oil, cornmeal, and honey samples at low microgram per gram (or microg/mL) levels with the CW agents or CW agent hydrolysis products. The detection limits observed for the CW agents in the spiked food samples ranged from 3 to 15 ng/mL in bottled water, 1-33 ng/mL in canola oil, 1-34 ng/g in cornmeal, and 13-18 ng/g in honey. Detection limits were much higher for the CW agent hydrolysis products, with only MPA being detected in spiked honey samples. PMID:17896827

Kolakowski, Beata M; D'Agostino, Paul A; Chenier, Claude; Mester, Zoltán

2007-11-01

164

Determination of total nitrofuran metabolites in shrimp muscle using liquid chromatography/tandem mass spectrometry in the atmospheric pressure chemical ionization mode.  

PubMed

The method of MacMahon and Lohne for analysis of nitrofuran metabolites in shrimp was optimized to streamline the extraction processes and the LC analysis. This revised method includes 16 h of mild acid hydrolysis/derivatization followed by ethyl acetate extraction and analysis by LC/MS/MS in the atmospheric pressure chemical ionization mode. This revised method was validated in shrimp for concentrations of 0.25 to 2.0 ng/g. The LOQ was 0.25 ng/g for all metabolites. The LOD was 0.052 nglg for 1-aminohydantoin (AHD), 0.206 ng/g for 3-amino-2-oxazolidinone (AOZ), 0.108 ng/g for semicarbazide (SC), and 0.062 ng/g for 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ). The spike recoveries with RSD into negative matrix at 1 ng/g were 100.2% (3.2%) for AHD, 102.5% (1.0%) for AOZ, 103.7% (2.3%) for SC, and 104.0% (3.3%) for AMOZ. The spike recoveries at 1 ng/g into unknown samples (n=108) containing varied levels of nitrofuran metabolites were 112.6% (25.7%) for AHD, 108.1% (12.1%) for AOZ, 103.0% (12.0%) for SC, and 100.3% (6.9%) for AMOZ. Interday precision with samples containing incurred AOZ concentrations of 0.92 to 17.8 ppb performed over a year was 10.4% RSD. The method is accurate and precise for determining nitrofuran concentrations in the edible tissue of shrimp. PMID:22970594

An, Haejung; Henry, Mark; Cain, Teresa; Tran, Bichsa; Paek, Han Chol; Farley, Dennis

2012-01-01

165

Use of gas chromatography/mass spectrometry with positive chemical ionization for the determination of opiates in human oral fluid.  

PubMed

An analytical method for the simultaneous determination of codeine, morphine and 6-acetylmorphine (6AM) in human oral fluid was developed. The method involves liquid-liquid extraction in Toxitubes A, derivatization with 99:1 (v/v) N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)/trimethylchlorosilane (TMCS), and gas chromatography/mass spectrometry with positive chemical ionization (GC/PCI-MS) determination. The detector response was linear over the concentration range 30-500 ng/mL with coefficients of correlation higher than 0.99. The precision was acceptable with coefficients of variation less than 7.5%. The limits of detection achieved were 0.7 ng/mL for codeine, 2.0 ng/mL for morphine, and 0.6 ng/mL for 6AM. The method proposed was applied to 80 oral fluid samples from opiates users, 98% of which were positive for the three analytes. Human oral fluid is a suitable biological fluid for the determination of opiates by GC/PCI-MS. PMID:16548052

Cámpora, Pamela; Bermejo, Ana María; Tabernero, María Jesús; Fernández, Purificación

2006-01-01

166

Self-Aspirated Atmospheric Pressure Chemical Ionization Source for Direct Sampling of Analytes on Surfaces and in Liquid Solutions  

SciTech Connect

A self-aspirating heated nebulizer probe is described and demonstrated for use in the direct analysis of analytes on surfaces and in liquid samples by atmospheric pressure chemical ionization (APCI) mass spectrometry. Functionality and performance of the probe as a self-aspirating APCI source is demonstrated using reserpine and progesterone as test compounds. The utility of the probe to sample analytes directly from surfaces was demonstrated first by scanning development lanes of a reversed-phase thin-layer chromatography plate in which a three-component dye mixture, viz., Fat Red 7B, Solvent Green 3, and Solvent Blue 35, was spotted and the components were separated. Development lanes were scanned by the sampling probe operated under computer control (x, y plane) while full-scan mass spectra were recorded using a quadrupole ion trap mass spectrometer. In addition, the ability to sample the surface of pharmaceutical tablets (viz., Extra Strength Tylenol(reg. sign) and Evista(reg. sign) tablets) and to detect the active ingredients (acetaminophen and raloxifene, respectively) selectively was demonstrated using tandem mass spectrometry (MS/MS). Finally, the capability to sample analyte solutions from the wells of a 384-well microtiter plate and to perform quantitative analyses using MS/MS detection was illustrated with cotinine standards spiked with cotinine-d{sub 3} as an internal standard.

Asano, Keiji G [ORNL; Ford, Michael J [ORNL; Tomkins, Bruce A [ORNL; Van Berkel, Gary J [ORNL

2005-01-01

167

Determination of triacylglycerols in donkey milk by using high performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry.  

PubMed

The separation and determination of triacylglycerols (TAGs), which are the main components of naturally occurring fats and oils, in milk fat is a challenging task due to the very complex nature of this matrix. In the present study the TAG fraction of donkey milk lipids has been characterized by using high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). HPLC in reversed phase mode has been used for TAG separation and silver ion (Ag+) HPLC has been used as a second dimension to clarify and confirm the identification. The RP-HPLC eluate was fractionated and the fractions of interest were injected onto the Ag+-HPLC column. In both cases peak assignment was carried out by combining retention data with APCI-MS spectra information. In total, 55 TAGs in donkey milk fat were identified (without considering the positional isomers) and quantified on the basis of percentage peak areas in the RP-HPLC chromatogram (without the use of correction factors). Amongst the identified triacylglycerols, POLn, POO, PPO, CaPO, POL, and PPoO proved to be the main components of the TAG fraction of donkey milk. PMID:16013829

Dugo, Paola; Kumm, Tiina; Lo Presti, Maria; Chiofalo, Biagina; Salimei, Elisabetta; Fazio, Alessia; Cotroneo, Antonella; Mondello, Luigi

2005-06-01

168

Chemical kinetics of low pressure high density hydrogen plasmas: application to negative ion sources for ITER  

NASA Astrophysics Data System (ADS)

This paper presents a systematic kinetic characterization of a low pressure high power hydrogen plasma. The plasma physics is described with a global model coupled to a homogeneous kinetic model for hydrogen. This model involves reactions which describe the vibrational and electronic excited kinetics of H2, the positive ?ft( H{+}{,}H2{+}{,}H3{+} \\right) and negative (H?) ion kinetics and the H chemistry. This enables the estimation of the particle density and the electron temperature and their evolutions as a function of power (1–100 kW) and pressure (0.3–4 Pa). These very specific plasma conditions involve physical phenomena not occurring in more usual plasmas, such as gas depletion. To account for this gas depletion, we incorporate in the global model both the H neutral heat equation to calculate the H temperature, and the gas pumping. Indeed, the gas depletion is mainly due to H atom heating leading to a higher pumping loss for H atoms. The consideration of the gas depletion allows us to obtain similar behaviors to the experiments when varying power and pressure. From an accurate analysis of the main formation and destruction pathways for each particle, the species kinetics is discussed and a simplified kinetic model that may be used to describe the non-equilibrium plasma in the negative source for ITER is proposed. Finally, the results point to strong coupling existing between the H atom wall recombination coefficient ?H and the gas depletion. An increase of ?H reduces the gas depletion, affecting the electron temperature and the electron density as well as the whole plasma kinetics.

Gaboriau, F.; Boeuf, J. P.

2014-12-01

169

Limitations of low resolution mass spectrometry in the electron capture negative ionization mode for the analysis of short- and medium-chain chlorinated paraffins.  

PubMed

The analysis of complex mixtures of chlorinated paraffins (CPs) with short (SCCPs, C(10)-C(13)) and medium (MCCPs, C(14)-C(17)) chain lengths can be disturbed by mass overlap, if low resolution mass spectrometry (LRMS) in the electron capture negative ionization mode is employed. This is caused by CP congeners with the same nominal mass, but with five carbon atoms more and two chlorine atoms less; for example C(11)H(17)(37)Cl(35)Cl(6) ( m/ z 395.9) and C(16)H(29)(35)Cl(5) ( m/ z 396.1). This can lead to an overestimation of congener group quantity and/or of total CP concentration. The magnitude of this interference was studied by evaluating the change after mixing a SCCP standard and a MCCP standard 1+1 (S+MCCP mixture) and comparing it to the single standards. A quantification of the less abundant C(16) and C(17) congeners present in the MCCP standard was not possible due to interference from the major C(11) and C(12) congeners in the SCCPs. Also, signals for SCCPs (C(10)-C(12)) with nine and ten chlorine atoms were mimicked by MCCPs (C(15)-C(17)) with seven and eight chlorine atoms (for instance C(10)H(12)Cl(10) by C(15)H(24)Cl(8)). A similar observation was made for signals from C(15)-C(17) CPs with four and five chlorine atoms resulting from SCCPs (C(10)-C(12)) with six and seven chlorine atoms (such as C(15)H(28)Cl(4) by C(10)H(16)Cl(6)) in the S+MCCP mixture. It could be shown that the quantification of the most abundant congeners (C(11)-C(14)) is not affected by any interference. The determination of C(10) and C(15) congeners is partly disturbed, but this can be detected by investigating isotope ratios, retention time ranges and the shapes of the CP signals. Also, lower chlorinated compounds forming [M+Cl](-) as the most abundant ion instead of [M-Cl](-) are especially sensitive to systematic errors caused by superposition of ions of different composition and the same nominal mass. PMID:14997265

Reth, Margot; Oehme, Michael

2004-04-01

170

A fast-response chemical ionization mass spectrometer for in situ measurements of HNO3 in the upper troposphere and lower stratosphere  

Microsoft Academic Search

A chemical ionization mass spectrometer instrument has been developed for in situ measurements of nitric acid (HNO3) in the upper troposphere and lower stratosphere from the NASA WB-57 aircraft. Fast and sensitive measurements of HNO3 are achieved by using a low surface area heated Teflon sampling inlet and detection techniques that employ ion-molecule reactions. Sensitivity to HNO3 is determined in

J. A. Neuman; R. S. Gao; M. E. Schein; S. J. Ciciora; J. C. Holecek; T. L. Thompson; R. H. Winkler; R. J. McLaughlin; M. J. Northway; E. C. Richard; D. W. Fahey

2000-01-01

171

Improved quantitative detection of 11 urinary phthalate metabolites in humans using liquid chromatography–atmospheric pressure chemical ionization tandem mass spectrometry  

Microsoft Academic Search

Phthalates are widely used as industrial solvents and plasticizers, with global use exceeding four million tons per year. We improved our previously developed high-performance liquid chromatography–atmospheric pressure chemical ionization-tandem mass spectrometric (HPLC–APCI-MS\\/MS) method to measure urinary phthalate metabolites by increasing the selectivity and the sensitivity by better resolving them from the solvent front, adding three more phthalate metabolites, monomethyl phthalate

Manori J Silva; Nicole A Malek; Carolyn C Hodge; John A Reidy; Kayoko Kato; Dana B Barr; Larry L Needham; John W Brock

2003-01-01

172

Analysis of aristolochic acid in nine sources of Xixin, a traditional Chinese medicine, by liquid chromatography\\/atmospheric pressure chemical ionization\\/tandem mass spectrometry  

Microsoft Academic Search

Aristolochic acid I (AA-I), which is a known nephrotoxin, is found in a commonly used Chinese medicine, Xixin, that originates from nine Asarum species (Aristolochiaceae) found in China. A method has been developed using reversed-phase liquid chromatography coupled with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry under the positive ion detection mode [LC\\/(+)APCI\\/MS\\/MS] to determine the amount of AA-I

Ting-Ting Jong; Maw-Rong Lee; Shun-Sheng Hsiao; Jar-Lung Hsai; Tian-Shung Wu; Shu Tuan Chiang; Shao-Qing Cai

2003-01-01

173

Rapid and sensitive analysis of azadirachtin and related triterpenoids from Neem ( Azadirachta indica) by high-performance liquid chromatography–atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

Based on reversed-phase high-performance liquid chromatography (RP-HPLC) and atmospheric pressure chemical ionization (APCI) mass spectrometry, a HPLC–MS method was developed to permit the rapid qualitative and quantitative analysis of azadirachtin and related tetranortriterpenoids from seeds and tissue cultures of Neem (Azadirachta indica). APCI+ standard scanning mass spectra of the major Neem triterpenoids were recorded and utilized to select suitable ions

Otmar Schaaf; Andrew P Jarvis; S. Andrew van der Esch; Germina Giagnacovo; Neil J Oldham

2000-01-01

174

Studies of soluble organics in simulated in situ oil-shale retort water by electron impact and chemical ionization from a combined gas chromatograph-mass spectrometer system  

Microsoft Academic Search

Retort water samples collected from the Laramie 10-ton simulated in-situ retort were examined by both electron impact (EI) and chemical ionization (CI) mass spectrometry with a Finnigan Model 3300 gas chromatograph--mass spectrometer (GC-MS). These water samples, formed in retorting Green River oil shale of either Utah or Colorado origin, were filtered, lyophilized, extracted with benzene, and esterified. Both the benzene

C. S. Wen; T. F. Yen; J. B. Knight; R. E. Poulson

1976-01-01

175

Simultaneous determination of fatty, dicarboxylic and amino acids based on derivatization with isobutyl chloroformate followed by gas chromatography—positive ion chemical ionization mass spectrometry  

Microsoft Academic Search

Gas chromatography–mass spectrometry (GC–MS) with positive ion chemical ionization (PICI) using isobutane as reagent gas was applied for analysis of isobutoxycarbonyl\\/isobutyl derivatives of 13 fatty, 6 dicarboxylic and 13 amino acids in a single run. For all investigated compounds (except several amino acids) the quasimolecular ions [MH]+ were registered. Asparagine underwent fragmentation via decarboxylation followed by elimination of OC4H9 ([M?117]+),

Tim G. Sobolevsky; Alexander I. Revelsky; Igor A. Revelsky; Barbara Miller; Vincent Oriedo

2004-01-01

176

Comparison of the positive and negative ion electrospray ionization and matrix-assisted laser desorption ionization-time-of-flight mass spectra of the reaction products of phosphatidylethanolamines and hypochlorous acid.  

PubMed

Phosphatidylethanolamines (PEs) react with HOCl under formation of the mono- and dichloramines which are easily converted into secondary products (nitriles and imines). PEs with unsaturated acyl residues also give chlorhydrines. The aim of this study was to investigate whether all products may be detected by electrospray ionization (ESI) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Results indicated that chloramines and imines are nearly exclusively detectable by ESI-MS, whereas all other products are detectable by both MALDI and ESI-MS. Therefore, ESI-MS is superior for the detection of chlorinated products of PEs. PMID:18295587

Richter, Grit; Schober, Celestina; Süss, Rosmarie; Fuchs, Beate; Birkemeyer, Claudia; Schiller, Jürgen

2008-05-01

177

Structural transformation with "negative volume expansion": chemical bonding and physical behavior of TiGePt.  

PubMed

The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10?%. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885?°C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2)?Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9)?Å, b = 3.89081(5)?Å, c = 7.5034(1)?Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9?eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties. PMID:22461109

Ackerbauer, S-V; Senyshyn, A; Borrmann, H; Burkhardt, U; Ormeci, A; Rosner, H; Schnelle, W; Gam?a, M; Gumeniuk, R; Ramlau, R; Bischoff, E; Schuster, J C; Weitzer, F; Leithe-Jasper, A; Tjeng, L H; Grin, Yu

2012-05-14

178

Determination of rice herbicides, their transformation products and clofibric acid using on-line solid-phase extraction followed by liquid chromatography with diode array and atmospheric pressure chemical ionization mass spectrometric detection.  

PubMed

A simultaneous method for the trace determination of acidic, neutral herbicides and their transformation products in estuarine waters has been developed through an on-line solid-phase extraction method followed by liquid chromatography with diode array and mass spectrometric detection. An atmospheric pressure chemical ionization (APCI) interface was used in the negative ionization mode after optimization of the main APCI parameters. Limits of detection ranged from 0.1 to 0.02 ng/ml for 50 ml of acidified estuarine waters preconcentrated into polymeric precolumns and using time-scheduled selected ion monitoring mode. Two degradation products of the acidic herbicides (4-chloro-2-methylphenol and 2,4-dichlorophenol) did not show good signal response using APCI-MS at the concentration studied due to the higher fragmentor voltage needed for their determination. For molinate and the major degradation product of propanil, 3,4-dichloroaniline, positive ion mode was needed for APCI-MS detection. The proposed method was applied to the determination of herbicides in drainage waters from rice fields of the Delta del Ebro (Spain). During the 3-month monitoring of the herbicides, 8-hydroxybentazone and 4-chloro-2-methylphenoxyacetic acid were successively found in those samples. PMID:10870691

Santos, T C; Rocha, J C; Barceló, D

2000-05-19

179

Observation of negative differential resistance and electrical bi-stability in chemically synthesized ZnO nanorods  

NASA Astrophysics Data System (ADS)

Zinc oxide nanorods/p-Si heterostructures have been fabricated by depositing the chemically synthesized ZnO nanorods on p-type silicon substrate. Heterostructure shows electrical bi-stability and negative differential resistance (NDR) only at the beginning of the forward bias region, and these phenomena have been explained with the help of energy band diagram. An explanation is proposed for the origin of electrical bi-stability in light of the electric field induced charge transfer across the junction, and the NDR phenomena could be attributed to interfacial traps and defect level that arises due to oxygen and zinc interstitial vacancies. Room temperature photoluminescence measurement of ZnO nanorods exhibits the emission peaks at about 466 nm and 566 nm which are attributed to oxygen vacancies and Zn interstitials. A correlation between NDR and blue emission phenomena in the ZnO nanorods due to defects states has been established.

Roy, Nandini; Chowdhury, Avijit; Roy, Asim

2014-06-01

180

Computational and Experimental Assessment of Benzene Cation Chemistry for the Measurement of Marine Derived Biogenic Volatile Organic Compounds with Chemical Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Chemical ionization mass spectrometry (CIMS) is a highly selective and sensitive technique for the measurement of trace gases in the atmosphere. However, competing side reactions and dependence on relative humidity (RH) can make the transition from the laboratory to the field challenging. Effective implementation of chemical ionization requires a thorough knowledge of the elementary steps leading to ionization of the analyte. We have recently investigated benzene cations for the detection of marine derived biogenic volatile organic compounds (BVOCs), such isoprene and terpene compounds, from algal bloom events. Our experimental results indicate that benzene ion chemistry is an attractive candidate for field measurements, and the RH dependence is weak. To further understand the advantages and limitations of this approach, we have also used electronic structure theory calculations to compliment the experimental work. These theoretical methods can provide valuable insight into the physical chemistry of ion molecule reactions including thermodynamical information, the stability of ions to fragmentation, and potential sources of interference such as dehydration to form isobaric ions. The combined experimental and computational approach also allows validation of the theoretical methods and will provide useful information towards gaining predictive power for the selection of appropriate reagent ions for future experiments.

Zoerb, M.; Kim, M.; Zimmermann, K.; Bertram, T. H.

2013-12-01

181

Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Analysis of Gram-Positive, Catalase-Negative Cocci Not Belonging to the Streptococcus or Enterococcus Genus and Benefits of Database Extension  

PubMed Central

Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry with a Bruker Daltonics microflex LT system was applied to 90 well-characterized catalase-negative, Gram-positive cocci not belonging to the streptococci or enterococci. Biotyper version 2.0.43.1 software was used singly or in combination with a database extension generated in this study with 51 collection strains from 16 genera. Most strains were identified by using both databases individually, and some were identified only by applying the combined database. Thus, the methodology is very useful and the generated database extension was helpful. PMID:22403420

Dargis, Rimtas; Hammer, Monja; Justesen, Ulrik Stenz; Nielsen, Xiaohui C.; Kemp, Michael

2012-01-01

182

High-throughput and simultaneous analysis of eight central-acting muscle relaxants in human plasma by ultra-performance liquid chromatography–tandem mass spectrometry in the positive and negative ionization modes  

Microsoft Academic Search

In this report, a high-throughput and sensitive method for analysis of eight central-acting muscle relaxants in human plasma\\u000a by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS\\/MS) in the positive and negative ionization modes\\u000a using tolbutamide as internal standard is presented. After pretreatment of a plasma sample by solid-phase extraction with\\u000a an Oasis HLB cartridge, muscle relaxants were analyzed by UPLC with

Tadashi Ogawa; Hideki Hattori; Rina Kaneko; Kenjiro Ito; Masae Iwai; Yoko Mizutani; Tetsuya Arinobu; Akira Ishii; Hiroshi Seno

2011-01-01

183

Determination of molecular weight distribution of aromatic components in petroleum products by chemical ionization mass spectrometry with chlorobenzene as reagent gas  

SciTech Connect

A chemical ionization mass spectrometic technique for direct determination of the the molecular weight distributions of the major aromatic components in liquid fuels and other petro-products is discussed. The basic mechanism involves selective charge exchange reactions between chlorobenzene cations and the substituted benzenes and naphthalenes present in the sample. Chlorobenzene also serves as the solvent for the fuel, and screening of successive samples can be carried out with a 3-min turn-around time. Depending upon conditions, the paraffinic components present in the fuel are absent in the resulting mass spectrum.

Sieck, L.W.

1983-01-01

184

Chemical composition of single aerosol particles at Idaho Hill: Positive ion measurements  

Microsoft Academic Search

The chemical compositions of single aerosol particles larger than 0.3 gm optical diameter were measured at Idaho Hill using a laser ionization mass spectrometer. The mass spectrometer can analyze either positive or negative ions; this paper covers the negative ion results. Sulfate, nitrate, organics, O-, and OH- were the most common peaks observed in the negative ion spectra. Other species

D. M. Murphy; D. S. Thomson

1997-01-01

185

Metal-organic chemical vapor-deposited cobalt oxide films as negative electrodes for thin film Li-ion battery  

NASA Astrophysics Data System (ADS)

In this study, thin films of cobalt oxide (Co3O4) have been grown by the metal-organic chemical vapor deposition (MOCVD) technique on stainless steel substrate at two preferred temperatures (450 °C and 500 °C), using cobalt acetylacetonate dihydrate as precursor. Spherical as well as columnar microstructures of Co3O4 have been observed under controlled growth conditions. Further investigations reveal these films are phase-pure, well crystallized and carbon-free. High-resolution TEM analysis confirms that each columnar structure is a continuous stack of minute crystals. Comparative study between these Co3O4 films grown at 450 °C and 500 °C has been carried out for their application as negative electrodes in Li-ion batteries. Our method of electrode fabrication leads to a coating of active material directly on current collector without any use of external additives. A high specific capacity of 1168 micro Ah cm-2 ?m-1 has been measured reproducibly for the film deposited at 500°C with columnar morphology. Further, high rate capability is observed when cycled at different current densities. The Co3O4 electrode with columnar structure has a specific capacity 38% higher than the electrode with spherical microstructure (grown at 450°C). Impedance measurements on the Co3O4 electrode grown at 500 °C also carried out to study the kinetics of the electrode process.

Jena, Anirudha; Munichandraiah, N.; Shivashankar, S. A.

2015-03-01

186

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX).  

PubMed

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H](+)) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H](+) ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d(15) provided evidence that [M+H](+) production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H](+) ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample. PMID:21435478

Smith, Philip A; Lepage, Carmela R Jackson; Savage, Paul B; Bowerbank, Christopher R; Lee, Edgar D; Lukacs, Michael J

2011-04-01

187

High-throughput and simultaneous analysis of eight central-acting muscle relaxants in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry in the positive and negative ionization modes.  

PubMed

In this report, a high-throughput and sensitive method for analysis of eight central-acting muscle relaxants in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in the positive and negative ionization modes using tolbutamide as internal standard is presented. After pretreatment of a plasma sample by solid-phase extraction with an Oasis HLB cartridge, muscle relaxants were analyzed by UPLC with Acquity UPLC BEH C(18) column and Acquity TQD tandem quadrupole mass spectrometer equipped with an electrospray ionization interface. The calibration curves for muscle relaxants spiked into human plasma equally showed good linearities in the nanogram per milliliter order range. The detection limits (signal-to-noise ratio?=?3) was as low as 0.1-2 ng/mL. The method gave satisfactory recovery rates, accuracy, and precision for quality control samples spiked with muscle relaxants. To further validate the present method, 250 mg of chlorphenesin carbamate was orally administered to a healthy male volunteer, and the concentrations of chlorphenesin carbamate in plasma were measured 0.5, 1, 2, 4, 6, and 8 h after dosing; their concentrations in human plasma were between 0.62 and 2.44 ?g/mL. To our knowledge, this is the first report describing simultaneous analysis of over more than two central-acting muscle relaxants by liquid chromatography-tandem mass spectrometry. This has been realized by the capability of our instrument for simultaneous multiple reaction monitoring of the target compounds in both positive and negative ionization modes. Therefore, the present method seems very useful in forensic and clinical toxicology and pharmacokinetic studies. PMID:21394449

Ogawa, Tadashi; Hattori, Hideki; Kaneko, Rina; Ito, Kenjiro; Iwai, Masae; Mizutani, Yoko; Arinobu, Tetsuya; Ishii, Akira; Seno, Hiroshi

2011-06-01

188

Ataxia telangiectasia: an inherited human disorder involving hypersensitivity to ionizing radiation and related DNA-damaging chemicals  

Microsoft Academic Search

This review is primarily devoted to ataxia telangiectasia - a complex multisystem disorder exhibiting many characteristics, both in vivo and in vitro, expected of an ionizing radiation analogue of XP. The recent upsurge of investigative interest in the cytotoxic, cytogenetic, and DNA repair properties of cultured AT cells after radiation treatment was prompted by the disclosure that AT patients are

M. C. Paterson; P. J. Smith

1979-01-01

189

THE JOURNAL OF CHEMICAL PHYSICS 135, 044702 (2011) Universal mechanism for breaking amide bonds by ionizing radiation  

E-print Network

by ionizing radiation Phillip S. Johnson,1 Peter L. Cook,1 Xiaosong Liu,2 Wanli Yang,2 Yiqun Bai,3 Nicholas L the two characteristic transitions at the N 1s edge. A variety of other models is considered and tested aromatic components absorb near-UV light). A va- riety of models for specific photodissociation processes

Himpsel, Franz J.

190

Zero-Net-Charge Air Ionizer  

NASA Technical Reports Server (NTRS)

Instrument monitors air supplied by air ionizer and regulates ionizer to ensure net charge neutral. High-impedance electrometer and nulling control amplifier regulate output of air ionizer. Primarily intended to furnish ionized air having no net charge, instrument adaptable to generating air with positive or negative net charge is so desired. Useful where integrated circuit chips are manufactured, inspected, tested or assembled.

Woods, W. R., Jr.

1985-01-01

191

Comparison of the concepts used to develop and apply occupational exposure limits for ionizing radiation and hazardous chemical substances  

Microsoft Academic Search

The rationales used by the American Conference of Governmental Industrial Hygienists (AC-GIH) to recommend exposure limits for 10 chemicals were reviewed. The 10 chemicals chosen were known to produce chronic disease after prolonged overexposure in the workplace. The chemicals were toluene diisocyanate, hydrogen fluoride, n-hexane, carbon disulfide, cadmium, inorganic mercury, cobalt, nitroglycerol, silica, and vinyl chloride. The rationales used by

D HALTON

1988-01-01

192

Thermal dissociation atmospheric chemical ionization ion trap mass spectrometry with a miniature source for selective trace detection of dimethoate in fruit juices.  

PubMed

A miniature thermal dissociation atmospheric chemical ionization (TDCI) source, coupled with LTQ-MS, has been developed for rapid trace detection of pesticide residues such as dimethoate in highly viscous fruit juice samples. Instead of toxic organic solvents and the high electric field used in the conventional ionizations, an ionic liquid, a "green solvent", was employed to directly generate reagent ions in the TDCI process, followed by the proton or charge transfer with the analytes prior to the LTQ instrument for mass analysis. Trace amounts of dimethoate in fresh orange juices have been quantitatively detected, without any sample pretreatment or aid of high-pressure gas. A low limit of detection (LOD = 8.76 × 10(-11) g mL(-1)), acceptable relative standard deviation (RSD = 3.1-10.0%), and reasonable recoveries (91.2-102.8%) were achieved with this method for direct detection of dimethoate in highly viscous orange juice samples. The average analysis time for each single sample was less than 30 seconds. These experimental results showed that the miniature TDCI developed here is a powerful tool for the fast trace detection of pesticide residues in complex viscous fruit juices, with the advantage of high sensitivity, high speed, and high-throughput, ease of operation, and so on. Because of no chemical contamination and high voltage damage to the analytes and the environment, the technique has promising applications for online quality monitoring in the area of food safety. PMID:23181260

Ouyang, Yongzhong; Zhang, Xinglei; Han, Jing; Guo, Xiali; Zhu, Zhiqiang; Chen, Huanwen; Luo, Liping

2013-01-21

193

Specificity enhancement by electrospray ionization multistage mass spectrometry--a valuable tool for differentiation and identification of 'V'-type chemical warfare agents.  

PubMed

The use of chemical warfare agents has become an issue of emerging concern. One of the challenges in analytical monitoring of the extremely toxic 'V'-type chemical weapons [O-alkyl S-(2-dialkylamino)ethyl alkylphosphonothiolates] is to distinguish and identify compounds of similar structure. MS analysis of these compounds reveals mostly fragment/product ions representing the amine-containing residue. Hence, isomers or derivatives with the same amine residue exhibit similar mass spectral patterns in both classical EI/MS and electrospray ionization-MS, leading to unavoidable ambiguity in the identification of the phosphonate moiety. A set of five 'V'-type agents, including O-ethyl S-(2-diisopropylamino)ethyl methylphosphonothiolate (VX), O-isobutyl S-(2-diethylamino)ethyl methylphosphonothiolate (RVX) and O-ethyl S-(2-diethylamino)ethyl methylphosphonothiolate (VM) were studied by liquid chromatography/electrospray ionization/MS, utilizing a QTRAP mass detector. MS/MS enhanced product ion scans and multistage MS(3) experiments were carried out. Based on the results, possible fragmentation pathways were proposed, and a method for the differentiation and identification of structural isomers and derivatives of 'V'-type chemical warfare agents was obtained. MS/MS enhanced product ion scans at various collision energies provided information-rich spectra, although many of the product ions obtained were at low abundance. Employing MS(3) experiments enhanced the selectivity for those low abundance product ions and provided spectra indicative of the different phosphonate groups. Study of the fragmentation pathways, revealing some less expected structures, was carried out and allowed the formulation of mechanistic rules and the determination of sets of ions typical of specific groups, for example, methylphosphonothiolates versus ethylphosphonothiolates. The new group-specific ions elucidated in this work are also useful for screening unknown 'V'-type agents and related compounds, utilizing precursor ion scan experiments. PMID:24338889

Weissberg, Avi; Tzanani, Nitzan; Dagan, Shai

2013-12-01

194

Effect of processing on surface roughness for a negative-tone chemically amplified resist exposed by x-ray lithography  

NASA Astrophysics Data System (ADS)

As critical dimensions for devices continue to shrink, there is concern over the possible resist sidewall contributions to the critical dimension error budget. Because top surface roughness is substantially easier to measure than the sidewall roughness, it is the purpose of this paper to correlate top surface and sidewall roughness to the processing parameters of dose and development conditions that effect the overall roughness and to explore some possible reasons for the differences in the top surface and sidewall roughness. Initial atomic force microscopy results on the resist top surface indicate that there is a general correlation between the top surface roughness and the processing conditions of dose and development. The sidewall roughness results, however, indicate that the sidewall roughness is relatively independent of the dose and development conditions for the negative-tone, chemically- amplified resist, Shipley SAL 605. The root mean square roughness (Rrms) for the resist sidewalls was on the order of 5.2 +/- 0.5 nm for X-ray exposure. The top surface roughness for the resist at optimized lithographic conditions of 80 mJ/cm2 developed with 0.254 N tetramethylammonium hydroxide was 7.2 +/- 1 nm. These studies, looking at the effects of dose, have shown that increasing the dose decreases the top surface roughness. The extent of the linking reaction, as measured by FTIR, has been compared to the roughness of the resist for samples that have the same approximate linking but have had radically different dose and thermal histories. These preliminary results indicate that there is a general correlation between the extent of linking and the roughness. Samples exposed to a very high dose (650 mJ/cm2) but subjected to short post-exposure bake times (4.1 sec at 108 degree(s)) show similar roughness to samples exposed with lower doses (150 mJ/cm2) but longer PEB times (40 sec at 108 degree(s)). The development conditions provide another major contributing factor in the top surface roughness. Decreasing the developer concentration decreases the top surface roughness of the resist. Adding particular quaternary ammonium salts to the developer decreases the surface roughness and slows the dissolution rate. The goal of these efforts with developer additives was to find the appropriate processing conditions that would yield surface roughness below 3 nm for 100 nm lines. This paper will also explore possible explanations for the effect of developer conditions on the observed roughness in light of current dissolution theories.

Reynolds, Geoffrey W.; Taylor, James W.

1998-06-01

195

Comparison of Bruker Biotyper Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometer to BD Phoenix Automated Microbiology System for Identification of Gram-Negative Bacilli?  

PubMed Central

We compared the BD Phoenix automated microbiology system to the Bruker Biotyper (version 2.0) matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (MS) system for identification of Gram-negative bacilli, using biochemical testing and/or genetic sequencing to resolve discordant results. The BD Phoenix correctly identified 363 (83%) and 330 (75%) isolates to the genus and species level, respectively. The Bruker Biotyper correctly identified 408 (93%) and 360 (82%) isolates to the genus and species level, respectively. The 440 isolates were grouped into common (308) and infrequent (132) isolates in the clinical laboratory. For the 308 common isolates, the BD Phoenix and Bruker Biotyper correctly identified 294 (95%) and 296 (96%) of the isolates to the genus level, respectively. For species identification, the BD Phoenix and Bruker Biotyper correctly identified 93% of the common isolates (285 and 286, respectively). In contrast, for the 132 infrequent isolates, the Bruker Biotyper correctly identified 112 (85%) and 74 (56%) isolates to the genus and species level, respectively, compared to the BD Phoenix, which identified only 69 (52%) and 45 (34%) isolates to the genus and species level, respectively. Statistically, the Bruker Biotyper overall outperformed the BD Phoenix for identification of Gram-negative bacilli to the genus (P < 0.0001) and species (P = 0.0005) level in this sample set. When isolates were categorized as common or infrequent isolates, there was statistically no difference between the instruments for identification of common Gram-negative bacilli (P > 0.05). However, the Bruker Biotyper outperformed the BD Phoenix for identification of infrequently isolated Gram-negative bacilli (P < 0.0001). PMID:21209160

Saffert, Ryan T.; Cunningham, Scott A.; Ihde, Sherry M.; Monson Jobe, Kristine E.; Mandrekar, Jayawant; Patel, Robin

2011-01-01

196

Physico-Chemical-Managed Killing of Penicillin-Resistant Static and Growing Gram-Positive and Gram-Negative Vegetative Bacteria  

NASA Technical Reports Server (NTRS)

Systems and methods for the use of compounds from the Hofmeister series coupled with specific pH and temperature to provide rapid physico-chemical-managed killing of penicillin-resistant static and growing Gram-positive and Gram-negative vegetative bacteria. The systems and methods represent the more general physico-chemical enhancement of susceptibility for a wide range of pathological macromolecular targets to clinical management by establishing the reactivity of those targets to topically applied drugs or anti-toxins.

Richmond, Robert Chaffee (Inventor); Schramm, Jr., Harry F. (Inventor); Defalco, Francis G. (Inventor); Farris, III, Alex F. (Inventor)

2012-01-01

197

A quantum chemical study from a molecular transport perspective: ionization and electron attachment energies for species often used to fabricate single-molecule junctions.  

PubMed

The accurate determination of the lowest electron attachment (EA) and ionization (IP) energies for molecules embedded in molecular junctions is important for correctly estimating, for example, the magnitude of the currents (I) or the biases (V) where an I-V curve exhibits significant non-Ohmic behavior. Benchmark calculations for the lowest electron attachment and ionization energies of several typical molecules utilized to fabricate single-molecule junctions characterized by n-type conduction (4,4'-bipyridine, 1,4-dicyanobenzene and 4,4'-dicyano-1,1'-biphenyl) and p-type conduction (benzenedithiol, biphenyldithiol, hexanemonothiol and hexanedithiol) based on the EOM-CCSD (equation-of-motion coupled-cluster singles and doubles) state-of-the-art method of quantum chemistry are presented. They indicate significant differences from the results obtained within current approaches to molecular transport. The present study emphasizes that, in addition to a reliable quantum chemical method, basis sets much better than the ubiquitous double-zeta set employed for transport calculations are needed. The latter is a particularly critical issue for correctly determining EAs, which is impossible without including sufficient diffuse basis functions. The spatial distribution of the dominant molecular orbitals (MOs) is another important issue, on which the present study draws attention, because it sensitively affects the MO energy shifts ? due to image charges formed in electrodes. The present results cannot substantiate the common assumption of a point-like MO midway between electrodes, which substantially affects the actual ?-values. PMID:25270244

Bâldea, Ioan

2014-01-01

198

Potential of gas chromatography-atmospheric pressure chemical ionization-time-of-flight mass spectrometry for the determination of sterols in human plasma.  

PubMed

The application of Gas Chromatography (GC)-Atmospheric Pressure Chemical Ionization (APCI)-Time-of-Flight Mass Spectrometry (TOF-MS) is presented for sterol analysis in human plasma. A commercial APCI interface was modified to ensure a well-defined humidity which is essential for controlled ionization. In the first step, optimization regarding flow rates of auxiliary gases was performed by using a mixture of model analytes. Secondly, the qualitative and quantitative analysis of sterols including oxysterols, cholesterol precursors, and plant sterols as trimethylsilyl-derivatives was successfully carried out. The characteristics of APCI together with the very good mass accuracy of TOF-MS data enable the reliable identification of relevant sterols in complex matrices. Linear calibration lines and plausible results for healthy volunteers and patients could be obtained whereas all mass signals were extracted with an extraction width of 20 ppm from the full mass data set. One advantage of high mass accuracy can be seen in the fact that from one recorded run any search for m/z can be performed. PMID:24463103

Matysik, S; Schmitz, G; Bauer, S; Kiermaier, J; Matysik, F-M

2014-04-11

199

Fast determination of 3-ethenylpyridine as a marker of environmental tobacco smoke at trace level using direct atmospheric pressure chemical ionization tandem mass spectrometry  

NASA Astrophysics Data System (ADS)

A method with atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) was developed and applied to direct analysis of Environmental Tobacco Smoke (ETS), using 3-ethenylpyridine (3-EP) as a vapour-phase marker. In this study, the ion source of APCI-MS/MS was modified and direct analysis of gas sample was achieved by the modified instrument. ETS samples were directly introduced, via an atmospheric pressure inlet, into the APCI source. Ionization was carried out in positive-ion APCI mode and 3-EP was identified by both full scan mode and daughter scan mode. Quantification of 3-EP was performed by multiple reaction monitoring (MRM) mode. The calibration curve was obtained in the range of 1-250 ng L-1 with a satisfactory regression coefficient of 0.999. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.5 ng L-1 and 1.6 ng L-1, respectively. The precision of the method, calculated as relative standard deviation (RSD), was characterized by repeatability (RSD 3.92%) and reproducibility (RSD 4.81%), respectively. In real-world ETS samples analysis, compared with the conventional GC-MS method, the direct APCI-MS/MS has shown better reliability and practicability in the determination of 3-EP at trace level. The developed method is simple, fast, sensitive and repeatable; furthermore, it could provide an alternative way for the determination of other volatile pollutants in ambient air at low levels.

Jiang, Cheng-Yong; Sun, Shi-Hao; Zhang, Qi-Dong; Liu, Jun-Hui; Zhang, Jian-Xun; Zong, Yong-Li; Xie, Jian-Ping

2013-03-01

200

Negative-tone CAR resists for e-beam lithography: modification of chemical composition for R&D application (high resolution) or production application (high sensitivity)  

NASA Astrophysics Data System (ADS)

In this study, it is investigated how chemical modifications of a given resist platform can induce improvements in e-beam lithographic performances. Molecular weight (Mw) as well as photo-acid generator (PAG) modifications will act as fine tuners for Sumitomo NEB-33 negative resist to match specific applications: preparation of advanced CMOS R&D architecture (highly resolving resists needed) and fast patterning for production environment (highly sensitive resists needed).

Charpin, Murielle; Pain, Laurent; Tedesco, Serge V.; Gourgon, C.; Andrei, A.; Henry, Daniel; LaPlanche, Yves; Hanawa, Ryotaro; Kusumoto, Tadashi; Suetsugu, Masumi; Yokoyama, H.

2002-07-01

201

Separation of triacylglycerols in a complex lipidic matrix by using comprehensive two-dimensional liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection.  

PubMed

The present investigation describes the employment of a comprehensive 2-D HPLC system, based on the combination of a silver ion and an RP column, for the characterization of the triacylglycerol (TAG) fraction of a very complex lipidic sample: donkey milk fat. The TAGs were grouped on the resulting bidimensional contour plot according to their double bond numbers (aligned along vertical bands) and according to their partition numbers (aligned along horizontal bands). Peak assignment was supported by using atmospheric pressure chemical ionization mass spectrometric (APCI-MS) detection. The combination of the enhanced resolving power of comprehensive multidimensional LC, the formation of ordered 2-D patterns, and APCI-MS detection proved to be an effective tool for the characterization of the complex matrix, enabling the separation and identification of nearly 60 TAGs. PMID:16830730

Dugo, Paola; Kumm, Tiina; Chiofalo, Biagina; Cotroneo, Antonella; Mondello, Luigi

2006-05-01

202

Simultaneous determination of fatty, dicarboxylic and amino acids based on derivatization with isobutyl chloroformate followed by gas chromatography-positive ion chemical ionization mass spectrometry.  

PubMed

Gas chromatography-mass spectrometry (GC-MS) with positive ion chemical ionization (PICI) using isobutane as reagent gas was applied for analysis of isobutoxycarbonyl/isobutyl derivatives of 13 fatty, 6 dicarboxylic and 13 amino acids in a single run. For all investigated compounds (except several amino acids) the quasimolecular ions [MH](+) were registered. Asparagine underwent fragmentation via decarboxylation followed by elimination of OC(4)H(9) ([M-117](+)), whereas serine and tyrosine produced the cluster ions [M+C(4)H(9)OCO](+). Estimated detection limits were 6-250 pg in the total ion current (TIC) mode and 3-10 times lower using the selected-ion monitoring (SIM) mode. PMID:14698242

Sobolevsky, Tim G; Revelsky, Alexander I; Revelsky, Igor A; Miller, Barbara; Oriedo, Vincent

2004-02-01

203

Dow and Kaw,eff vs. Kow and Kaw degrees: acid/base ionization effects on partitioning properties and screening commercial chemicals for long-range transport and bioaccumulation potential.  

PubMed

A set of 543 ionizable commercial organic compounds with various acid/base functionalities and experimental octanol-water partitioning coefficients (log Kow) were obtained from the Canadian Domestic Substances List. Corresponding pH-dependent octanol-water distribution coefficients (log Dow) and air-water partitioning coefficients (log Kaw,eff) were estimated using the SPARC software program, as were log Kow and log Kaw degrees values for the neutral forms of each chemical. Significant ionization dependent effects on chemical screening results at various pH values were obtained using established criteria for bioaccumulation potential (BAP) in aquatic organisms, terrestrial animals, and humans, as well as for atmospheric long range transport potential (LRTP). Future modelling efforts for environmental and toxicological screening of commercial chemicals should therefore explicitly include the influence of ionization for both weak and strong organic acids and bases on bioavailability and air-water mobility within the respective regulatory frameworks. Functional group specific sorption of both ionizable and neutral compounds to particulate and dissolved inorganic and organic matter will also affect chemical screening results for BAP and LRTP. More complex sorption related modelling in various types of representative aquatic systems also appears necessary to achieve reliable chemical screening results for commercial organic compounds. PMID:20721799

Rayne, Sierra; Forest, Kaya

2010-10-01

204

Application of high-resolution time-of-flight chemical ionization mass spectrometry measurements to estimate volatility distributions of ?-pinene and naphthalene oxidation products  

NASA Astrophysics Data System (ADS)

Recent developments in high-resolution time-of-flight chemical ionization mass spectrometry (HR-ToF-CIMS) have made it possible to directly detect atmospheric organic compounds in real time with high sensitivity and with little or no fragmentation, including low-volatility, highly oxygenated organic vapors that are precursors to secondary organic aerosol formation. Here, using ions identified by high-resolution spectra from an HR-ToF-CIMS with acetate reagent ion chemistry, we develop an algorithm to estimate the vapor pressures of measured organic acids. The algorithm uses identified ion formulas and calculated double bond equivalencies, information unavailable in quadrupole CIMS technology, as constraints for the number of possible oxygen-containing functional groups. The algorithm is tested with acetate chemical ionization mass spectrometry (acetate-CIMS) spectra of O3 and OH oxidation products of ?-pinene and naphthalene formed in a flow reactor with integrated OH exposures ranged from 1.2 × 1011 to 9.7 × 1011 molec s cm-3, corresponding to approximately 1.0 to 7.5 days of equivalent atmospheric oxidation. Measured gas-phase organic acids are similar to those previously observed in environmental chamber studies. For both precursors, we find that acetate-CIMS spectra capture both functionalization (oxygen addition) and fragmentation (carbon loss) as a function of OH exposure. The level of fragmentation is observed to increase with increased oxidation. The predicted condensed-phase secondary organic aerosol (SOA) average acid yields and O/C and H/C ratios agree within uncertainties with previous chamber and flow reactor measurements and ambient CIMS results. While acetate reagent ion chemistry is used to selectively measure organic acids, in principle this method can be applied to additional reagent ion chemistries depending on the application.

Chhabra, P. S.; Lambe, A. T.; Canagaratna, M. R.; Stark, H.; Jayne, J. T.; Onasch, T. B.; Davidovits, P.; Kimmel, J. R.; Worsnop, D. R.

2015-01-01

205

Electronic dynamics by ultrafast pump photoelectron detachment probed by ionization: a dynamical simulation of negative-neutral-positive in LiH(-).  

PubMed

The control of electronic dynamics in the neutral electronic states of LiH before the onset of significant nuclei motion is investigated using a negative-neutral-positive (NeNePo) ultrafast IR pump-attoescond pulse train (APT) probe scheme. Starting from the ground state of the anion (LiH(-)), multiphoton ultrafast electron detachment and subsequent excitation of the neutral by a few femtosecond intense IR pulse produces a non-equilibrium electronic density in neutral LiH. The coherent electronic wave packet is then probed by angularly resolved photoionization to the cation by an APT generated from a replica of the pump IR pulse at several time delays. Realistic parameters for the pump and the APT are used. Several NeNePo schemes are simulated using different IR carrier frequencies, showing that the delay between the successive attosecond pulses in the train can be used as a filter to probe the different pairs of states present in the coherent electronic wave packet produced by the pump pulse. The dynamical simulations include the pump and the probe pulses to all orders by solving the time-dependent Schrödinger equation using a coupled equation scheme for the manifolds of the anion, neutral, and cation subspaces. We show that an incomplete molecular orientation of the molecule in the laboratory frame does not prevent probing the electronic density localization by angularly resolved photoelectron maps. PMID:24936939

Mignolet, B; Levine, R D; Remacle, F

2014-08-21

206

Photochemical Dimerization of Dibenzylideneacetone: A Convenient Exercise in [2+2] Cycloaddition Using Chemical Ionization Mass Spectrometry  

ERIC Educational Resources Information Center

Chemical reactions induced by light have been utilized for synthesizing highly strained, thermodynamically unstable compounds, which are inaccessible through non-photochemical methods. Photochemical cycloaddition reactions, especially those leading to the formation of four-membered rings, constitute a convenient route to compounds that are…

Rao, G. Nageswara; Janardhana, Chelli; Ramanathan, V.; Rajesh, T.; Kumar, P. Harish

2006-01-01

207

Chemical analysis of pharmaceuticals and explosives in fingermarks using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry.  

PubMed

Chemical analysis of latent fingermarks, "touch chemistry," has the potential of providing intelligence or forensically relevant information. Matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI/TOF MS) was used as an analytical platform for obtaining mass spectra and chemical images of target drugs and explosives in fingermark residues following conventional fingerprint development methods and MALDI matrix processing. There were two main purposes of this research: (1) develop effective laboratory methods for detecting drugs and explosives in fingermark residues and (2) determine the feasibility of detecting drugs and explosives after casual contact with pills, powders, and residues. Further, synthetic latent print reference pads were evaluated as mimics of natural fingermark residue to determine if the pads could be used for method development and quality control. The results suggest that artificial amino acid and sebaceous oil residue pads are not suitable to adequately simulate natural fingermark chemistry for MALDI/TOF MS analysis. However, the pads were useful for designing experiments and setting instrumental parameters. Based on the natural fingermark residue experiments, handling whole or broken pills did not transfer sufficient quantities of drugs to allow for definitive detection. Transferring drugs or explosives in the form of powders and residues was successful for preparing analytes for detection after contact with fingers and deposition of fingermark residue. One downfall to handling powders was that the analyte particles were easily spread beyond the original fingermark during development. Analyte particles were confined in the original fingermark when using transfer residues. The MALDI/TOF MS was able to detect procaine, pseudoephedrine, TNT, and RDX from contact residue under laboratory conditions with the integration of conventional fingerprint development methods and MALDI matrix. MALDI/TOF MS is a nondestructive technique which provides chemical information in both the mass spectra and chemical images. PMID:24447453

Kaplan-Sandquist, Kimberly; LeBeau, Marc A; Miller, Mark L

2014-02-01

208

Basic Vapor Exposure for Tuning the Charge State Distribution of Proteins in Negative Electrospray Ionization: Elucidation of Mechanisms by Fluorescence Spectroscopy  

NASA Astrophysics Data System (ADS)

Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH- ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors.

Girod, Marion; Antoine, Rodolphe; Dugourd, Philippe; Love, Craig; Mordehai, Alex; Stafford, George

2012-07-01

209

Basic vapor exposure for tuning the charge state distribution of proteins in negative electrospray ionization: elucidation of mechanisms by fluorescence spectroscopy.  

PubMed

Manipulation for simplifying or increasing the observed charge state distributions of proteins can be highly desirable in mass spectrometry experiments. In the present work, we implemented a vapor introduction technique to an Agilent Jet Stream ESI (Agilent Technologies, Santa Clara, CA, USA) source. An apparatus was designed to allow for the enrichment of the nitrogen sheath gas with basic vapors. An optical setup, using laser-induced fluorescence and a pH-chromic dye, permits the pH profiling of the droplets as they evaporate in the electrospray plume. Mechanisms of pH droplet modification and its effect on the protein charging phenomenon are elucidated. An important finding is that the enrichment with basic vapors of the nitrogen sheath gas, which surrounds the nebulizer spray, leads to an increase in the spray current. This is attributed to an increase in the electrical conductivity of water-amine enriched solvent at the tip exit. Here, the increased current results in a generation of additional electrolytically produced OH(-) ions and a corresponding increase in the pH at the tip exit. Along the electrospray plume, the pH of the droplets increases due to both droplet evaporation and exposure to basic vapors from the seeded sheath gas. The pH evolution in the ESI plume obtained using pure and basic seeded sheath gas was correlated with the evolution of the charge state distribution observed in mass spectra of proteins, in the negative ion mode. Taking advantage of the Agilent Jet Stream source geometry, similar protein charge state distributions and ion intensities obtained with basic initial solutions, can be obtained using native solution conditions by seeding the heated sheath gas with basic vapors. PMID:22565506

Girod, Marion; Antoine, Rodolphe; Dugourd, Philippe; Love, Craig; Mordehai, Alex; Stafford, George

2012-07-01

210

Chemical reactivity of alkenes and alkynes as seen from activation energies, enthalpies of protonation, and carbon 1s ionization energies.  

PubMed

Electrophilic addition to multiple carbon-carbon bonds has been investigated for a series of twelve aliphatic and aromatic alkenes and the corresponding alkynes. For all molecules, enthalpies of protonation and activation energies for HCl addition across the multiple bonds have been calculated. Considering the protonation process as a cationic limiting case of electrophilic addition, the sets of protonation enthalpies and gas-phase activation energies allow for direct comparison between double- and triple-bond reactivities in both ionic and dipolar electrophilic reactions. The results from these model reactions show that the alkenes have similar or slightly lower enthalpies of protonation, but have consistently lower activation energies than do the alkynes. These findings are compared with results from high resolution carbon 1s photoelectron spectra measured in the gas phase, where the contribution from carbons of the unsaturated bonds are identified. Linear correlations are found for both protonation and activation energies as functions of carbon 1s energies. However, there are deviations from the lines that reflect differences between the three processes. Finally, substituent effects for alkenes and alkynes are compared using both activation and carbon 1s ionization energies. PMID:23050665

Holme, Alf; Sæthre, Leif J; Børve, Knut J; Thomas, T Darrah

2012-11-16

211

Direct probe atmospheric pressure photoionization/atmospheric pressure chemical ionization high-resolution mass spectrometry for fast screening of flame retardants and plasticizers in products and waste.  

PubMed

In this study, we develop fast screening methods for flame retardants and plasticizers in products and waste based on direct probe (DP) atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI) coupled to a high-resolution (HR) time-of-flight mass spectrometer. DP-APPI is reported for the first time in this study, and DP-APCI that has been scarcely exploited is optimized for comparison. DP-APPI was more selective than DP-APCI and also more sensitive for the most hydrophobic compounds. No sample treatment was necessary, and only a minimal amount of sample (few milligrams) was used for analysis that was performed within a few minutes. Both methods were applied to the analysis of plastic products, electronic waste, and car interiors. Polybrominated diphenylethers, new brominated flame retardants, and organophosphorus flame retardants were present in most of the samples. The combination of DP with HR mass spectra and data processing based on mass accuracy and isotopic patterns allowed the unambiguous identification of chemicals at low levels of about 0.025 % (w/w). Under untargeted screening, resorcinol bis(biphenylphosphate) and bisphenol A bis(bisphenylphosphate) were identified in many of the consumer products of which literature data are still very limited. PMID:24493336

Ballesteros-Gómez, A; Brandsma, S H; de Boer, J; Leonards, P E G

2014-04-01

212

Chemical analysis of raw and processed Fructus arctii by high-performance liquid chromatography/diode array detection-electrospray ionization-mass spectrometry  

PubMed Central

Background: In traditional Chinese medicine (TCM), raw and processed herbs are used to treat the different diseases. Fructus Arctii, the dried fruits of Arctium lappa l. (Compositae), is widely used in the TCM. Stir-frying is the most common processing method, which might modify the chemical compositions in Fructus Arctii. Materials and Methods: To test this hypothesis, we focused on analysis and identification of the main chemical constituents in raw and processed Fructus Arctii (PFA) by high-performance liquid chromatography/diode array detection-electrospray ionization-mass spectrometry. Results: The results indicated that there was less arctiin in stir-fried materials than in raw materials. however, there were higher levels of arctigenin in stir-fried materials than in raw materials. Conclusion: We suggest that arctiin reduced significantly following the thermal conversion of arctiin to arctigenin. In conclusion, this finding may shed some light on understanding the differences in the therapeutic values of raw versus PFA in TCM. PMID:25422559

Qin, Kunming; Liu, Qidi; Cai, Hao; Cao, Gang; Lu, Tulin; Shen, Baojia; Shu, Yachun; Cai, Baochang

2014-01-01

213

Chemical actions of ionizing radiation on oligopeptide derivatives of glycine in the neutral (Zwitterion) and basic forms  

SciTech Connect

Effects of protonation of the terminal NH/sub 2/ group on the relative yields of reductive deamination and deamidation by e/sup -/ in the ..gamma..-radiolysis of di, tri and tetra glycine in the solid state are described. The experimental data provide direct chemical evidence of specific sites of addition of e/sup -/ to c = o bonds along the peptide chain.

Garrison, W.M.; Sokol, H.A.

1980-01-01

214

Dicarboxylic degradation products of nonylphenol polyethoxylates: synthesis and identification by gas chromatography-mass spectrometry using electron and chemical ionization modes.  

PubMed

The synthesis, mass spectra and detectability of four selected dicarboxylic degradation products (CAPECs) of nonylphenol polyethoxylates (NPEOs) are reported. The selected isomers have an alpha,alpha-dimethyl configuration (expressed as "dm" in their abbreviation), five to eight C atoms and a carboxyl group in the alkyl chain, and a carboxymethoxy acid group (dm-CA5-8P1ECs). The synthesis was successfully accomplished via a reaction sequence that started from anisole. After trimethylsilylation with N,O-bis(trimethylsilyl)acetamide or methylation with (trimethylsilyl)diazomethane, the derivatives of the dm-CA5-8P1ECs were subjected to a GC-electron ionization (EI)-MS and GC-isobutane chemical ionization (CI)-MS. In EI-MS, ion peaks at m/z = 265 and 207, corresponding to the alpha,alpha-dimethyl structures via the benzyl cleavage of carboxyalkyl chain, were the most significant ions of the trimethylsilyl and methyl derivatives, respectively. In CI-MS, the main ion peaks of dm-CA5-, dm-CA6-, dm-CA7-, and dm-CA8P1EC after methylation were at m/z= 129, 143, 157, and 171, respectively, corresponding to the loss of methyl phenoxyacetate from [M+ H]+; meanwhile significant peaks were detected at 321, 335, 349, and 363, corresponding to the loss of the trimethylsilanol after trimethylsilylation. The potential for the identification and quantification of individual branched carboxyalkyl isomeric mixtures of CA5-, CA6-, CA7-, and CA8P1EC metabolites based on corresponding dm-CA5-8P1ECs revealed the advantage of the GC-CI-MS although the detection limits in CI were clearly higher than those in EI. PMID:15633752

Hoai, Pham Manh; Tsunoi, Shinji; Ike, Michihiko; Inui, Naoko; Tanaka, Minoru; Fujita, Masanori

2004-12-17

215

Comprehensive 2-dimensional gas chromatography fast quadrupole mass spectrometry (GC × GC-qMS) for urinary steroid profiling: mass spectral characteristics with chemical ionization.  

PubMed

Comprehensive 2-dimensional gas chromatography (GC × GC), coupled to either a time of flight mass spectrometry (TOF-MS) or a fast scanning quadrupole MS (qMS) has greatly increased the peak capacity and separation space compared to conventional GC-MS. However, commercial GC × GC-TOFMS systems are not equipped with chemical ionization (CI) and do not provide dominant molecular ions or enable single ion monitoring for maximal sensitivity. A GC × GC-qMS in mass scanning mode was investigated with electron ionization (EI) and positive CI (PCI), using CH(4) and NH(3) as reagent gases. Compared to EI, PCI-NH(3) produced more abundant molecular ions and high mass, structure-specific ions for steroid acetates. Chromatography in two dimensions was optimized with a mixture of 12 endogenous and 3 standard acetylated steroids (SM15-AC) relevant to doping control. Eleven endogenous target steroid acetates were identified in normal urine based on their two retention times, and EI and PCI-NH(3) mass spectra; nine of these endogenous target steroid acetates were identified in congenital adrenal hyperplasia (CAH) patients. The difference between the urinary steroids profiles of normal individuals and those from CAH patients can easily be visually distinguished by their GC × GC-qMS chromatograms. We focus here on the comparison and interpretation of the various mass spectra of the targeted endogenous steroids. PCI-NH(3) mass spectra were most useful for unambiguous molecular weight determination and for establishing the number of -OH by the losses of one or more acetate groups. We conclude that PCI-NH(3) with GC × GC-qMS provides improved peak capacity and pseudomolecular ions with structural specificity. PMID:22147458

Zhang, Ying; Tobias, Herbert J; Auchus, Richard J; Brenna, J Thomas

2011-01-01

216

Measurement of low-ppm mixing ratios of water vapor in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

A chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor (H2O) at low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A low-pressure flow of sample air passes through an ionization volume containing an ?-particle radiation source, resulting in a cascade of ion-molecule reactions that produce hydronium ions (H3O+) from ambient H2O. The production of H3O+ ions from ambient H2O depends on pressure and flow through the ion source, which were tightly controlled in order to maintain the measurement sensitivity independent of changes in the airborne sampling environment. The instrument was calibrated every 45 min in flight by introducing a series of H2O mixing ratios between 0.5 and 153 parts per million (ppm) generated by Pt-catalyzed oxidation of H2 standards while overflowing the inlet with dry synthetic air. The CIMS H2O instrument was deployed in an unpressurized payload area aboard the NASA WB-57 high altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The instrument performed successfully during seven flights, measuring H2O mixing ratios below 5 ppm in the lower stratosphere at altitudes up to 17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz and reported as 1-s averages. In-flight calibrations demonstrated a typical sensitivity of 2000 Hz ppm-1 at 3 ppm with a signal to noise ratio (2?, 1-s) greater than 32. The total measurement uncertainty was 9 to 11%, derived from the uncertainty in the in situ calibrations.

Thornberry, T. D.; Rollins, A. W.; Gao, R. S.; Watts, L. A.; Ciciora, S. J.; McLaughlin, R. J.; Voigt, C.; Hall, B.; Fahey, D. W.

2013-01-01

217

Measurement of low-ppm mixing ratios of water vapor in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

A chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor (H2O) at low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A low-pressure flow of sample air passes through an ionization volume containing an ?-particle radiation source, resulting in a cascade of ion-molecule reactions that produce hydronium ions (H3O+) from ambient H2O. The production of H3O+ ions from ambient H2O depends on pressure and flow through the ion source, which were tightly controlled in order to maintain the measurement sensitivity independent of changes in the airborne sampling environment. The instrument was calibrated every 45 min in flight by introducing a series of H2O mixing ratios between 0.5 and 153 parts per million (ppm, 10-6 mol mol-1) generated by Pt-catalyzed oxidation of H2 standards while overflowing the inlet with dry synthetic air. The CIMS H2O instrument was deployed in an unpressurized payload area aboard the NASA WB-57F high-altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The instrument performed successfully during seven flights, measuring H2O mixing ratios below 5 ppm in the lower stratosphere at altitudes up to 17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz and reported as 1 s averages. In-flight calibrations demonstrated a typical sensitivity of 2000 Hz ppm-1 at 3 ppm with a signal to noise ratio (2 ?, 1 s) greater than 32. The total measurement uncertainty was 9 to 11%, derived from the uncertainty in the in situ calibrations.

Thornberry, T. D.; Rollins, A. W.; Gao, R. S.; Watts, L. A.; Ciciora, S. J.; McLaughlin, R. J.; Voigt, C.; Hall, B.; Fahey, D. W.

2013-06-01

218

Highly sensitive and selective analysis of urinary steroids by comprehensive two-dimensional gas chromatography combined with positive chemical ionization quadrupole mass spectrometry  

PubMed Central

Comprehensive two dimensional gas chromatography (GC×GC) provides greater separation space than conventional GC. Because of fast peak elution, a time of flight mass spectrometer (TOFMS) is the usual structure-specific detector of choice. The quantitative capabilities of a novel GC×GC fast quadrupole MS were investigated with electron ionization (EI), and CH4 or NH3 positive chemical ionization (PCI) for analysis of endogenous urinary steroids targeted in anti-doping tests. Average precisions for steroid quantitative analysis from replicate urine extractions were 6% (RSD) for EI and 8% for PCI-NH3. The average limits of detection (LOD) calculated by quantification ions for 12 target steroids spiked into steroid-free urine matrix (SFUM) were 2.6 ng mL?1 for EI, 1.3 ng mL?1 for PCI-CH4, and 0.3 ng mL?1 for PCI-NH3, all in mass scanning mode. The measured limits of quantification (LOQ) with full mass scan GC×GC-qMS were comparable with the LOQ values measured by one-dimensional GC-MS in single ion monitoring (SIM) mode. PCI-NH3 yields fewer fragments and greater (pseudo)molecular ion abundances than EI or PCI-CH4. These data show a benchtop GC×GC-qMS system has the sensitivity, specificity, and resolution to analyze urinary steroids at normal urine concentrations, and that PCI-NH3, not currently available on most GC×GC-TOFMS instruments, is of particular value for generation of structure-specific ions. PMID:22606686

Zhang, Ying; Tobias, Herbert J.; Brenna, J. Thomas

2014-01-01

219

Chemical Ionization Mass Spectrometry-Based Measurements of HO2 and RO2 During TRACE-P  

NASA Technical Reports Server (NTRS)

The Transport and Chemical Evolution over the Pacific (TRACE-P) mission extends NASA's Global Tropospheric Experiment (GTE) series of campaigns. TRACE-P was an aircraft-based campaign that was part of a larger ground-based and aircraft-based program (APARE) under the auspices of the International Global Atmospheric Chemistry (IGAC) program. TRACE-P was designed to (1) determine the chemical composition of Asian outflow over the western Pacific, and to (2) determine the chemical evolution of the Asian outflow. These objectives were addressed through a variety of observations and numerical modeling exercises. In particular, the goals included sampling strategies that would improve understanding of the budgets of odd hydrogen species (OH and HO2), budgets of NOx (NO, NO2, and their reservoirs), and impacts of oxidants produced in the outflow on air quality in the United States. The NASA DC-8 and P-3B aircraft were deployed in the March and April, 2001 out of primary bases of operation in Hong Kong and Yokota Air Base in Japan. These two aircraft have complementary capabilities which allow high altitude and long range impacts, as well as low altitude, local impacts to be assessed. In order to quantify the composition and evolution of Asian outflow, it is important to quantify as many species as possible including photochemically active species (e.g. NO2, CH2O, O3, acetone, etc.), sources species (VOCs, CO, NOx, SO2, aerosols), reactive intermediates including free radicals (OH, HO2, RO2, and their reservoirs), and end products (nitric acid, sulfuric acid, secondary aerosols, etc.). The more complete the measurement suite, the more tightly constrained the numerical modeling can be (within the uncertainties of the measurements). The numerical models range in sophistication from simple steady state box models (as employed in this study) to multi-dimensional chemical transport models. Data were collected on approximately 20 flights of the DC-8 and 21 flights of the P-3B. Observations from both aircraft were used in the present analysis, but primarily focused on the P-3B flights since that was the platform on which the peroxy radical instrumentation was based.

Cantrell, Christopher A.; Eisele, Fred L.

2004-01-01

220

Amorphous silicon ionizing particle detectors  

DOEpatents

Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation.

Street, Robert A. (Palo Alto, CA); Mendez, Victor P. (Berkeley, CA); Kaplan, Selig N. (El Cerrito, CA)

1988-01-01

221

Amorphous silicon ionizing particle detectors  

DOEpatents

Amorphous silicon ionizing particle detectors having a hydrogenated amorphous silicon (a--Si:H) thin film deposited via plasma assisted chemical vapor deposition techniques are utilized to detect the presence, position and counting of high energy ionizing particles, such as electrons, x-rays, alpha particles, beta particles and gamma radiation. 15 figs.

Street, R.A.; Mendez, V.P.; Kaplan, S.N.

1988-11-15

222

Microprobe sampling--photo ionization-time-of-flight mass spectrometry for in situ chemical analysis of pyrolysis and combustion gases: examination of the thermo-chemical processes within a burning cigarette.  

PubMed

A microprobe sampling device (?-probe) has been developed for in situ on-line photo ionization mass spectrometric analysis of volatile chemical species formed within objects consisting of organic matter during thermal processing. With this approach the chemical signature occurring during heating, pyrolysis, combustion, roasting and charring of organic material within burning objects such as burning fuel particles (e.g., biomass or coal pieces), lit cigarettes or thermally processed food products (e.g., roasting of coffee beans) can be investigated. Due to its dynamic changes between combustion and pyrolysis phases the cigarette smoking process is particularly interesting and has been chosen as first application. For this investigation the tip of the ?-probe is inserted directly into the tobacco rod and volatile organic compounds from inside the burning cigarette are extracted and real-time analyzed as the glowing front (or coal) approaches and passes the ?-probe sampling position. The combination of micro-sampling with photo ionization time-of-flight mass spectrometry (PI-TOFMS) allows on-line intrapuff-resolved analysis of species formation inside a burning cigarette. Monitoring volatile smoke compounds during cigarette puffing and smoldering cycles in this way provides unparalleled insights into formation mechanisms and their time-dependent change. Using this technique the changes from pyrolysis conditions to combustion conditions inside the coal of a cigarette could be observed directly. A comparative analysis of species formation within a burning Kentucky 2R4F reference cigarette with ?-probe analysis reveals different patterns and behaviors for nicotine, and a range of semi-volatile aromatic and aliphatic species. PMID:22244143

Hertz, Romy; Streibel, Thorsten; Liu, Chuan; McAdam, Kevin; Zimmermann, Ralf

2012-02-10

223

Wafer Treatment Using Electrolysis-Ionized Water  

NASA Astrophysics Data System (ADS)

Electrolysis-ionized water treatment is shown to be useful for removing polystyrene particles from contact holes, silicon surface cleaning and the removal of metal contamination such as copper. Electrolysis-ionized waterhas a controllable pH and a higher oxidation-reduction potential than chemicals. Moreover, this water does notcontain acid or alkaline chemicals, and can easily be neutralized without adding chemicals. Electrolysis-ionized water treatment has great potential for ecologically safe and low cost semiconductor processing.

Aoki, Hidemitsu; Nakamori, Masaharu; Aoto, Nahomi; Ikawa, Eiji

1994-10-01

224

An advanced method for the determination of carboxyl methyl esterase activity using gas chromatography-chemical ionization-mass spectrometry.  

PubMed

We developed a quantitative method for the determination of methyl esterase activity, analyzing substrate specificity against three major signal molecules, jasmonic acid methyl ester (MeJA), salicylic acid methyl ester (MeSA), and indole-3-acetic acid methyl ester (MeIAA). We used a silylation reagent for chemical derivatization and used gas chromatography (GC)-mass spectroscopy in analyses, for high precision. To test this method, an Arabidopsis esterase gene, AtME8, was expressed in Escherichia coli, and then the kinetic parameters of the recombinant enzyme were determined for three substrates. Finally, this method was also applied to the direct quantification of phytohormones in petals from lilies and roses. PMID:18255361

Koo, Yeon Jong; Yoon, Eunsil; Song, Jong Tae; Seo, Hak Soo; Kim, Jeong-Han; Lee, Yin-Won; Lee, Jong Seob; Cheong, Jong-Joo; Choi, Yang Do

2008-02-15

225

Negative ion source  

DOEpatents

An ionization vessel is divided into an ionizing zone and an extraction zone by a magnetic filter. The magnetic filter prevents high-energy electrons from crossing from the ionizing zone to the extraction zone. A small positive voltage impressed on a plasma grid, located adjacent an extraction grid, positively biases the plasma in the extraction zone to thereby prevent positive ions from migrating from the ionizing zone to the extraction zone. Low-energy electrons, which would ordinarily be dragged by the positive ions into the extraction zone, are thereby prevented from being present in the extraction zone and being extracted along with negative ions by the extraction grid. Additional electrons are suppressed from the output flux using ExB drift provided by permanent magnets and the extractor grid electrical field.

Leung, Ka-Ngo (Hercules, CA); Ehlers, Kenneth W. (Alamo, CA)

1984-01-01

226

Negative ion source  

DOEpatents

An ionization vessel is divided into an ionizing zone and an extraction zone by a magnetic filter. The magnetic filter prevents high-energy electrons from crossing from the ionizing zone to the extraction zone. A small positive voltage impressed on a plasma grid, located adjacent an extraction grid, positively biases the plasma in the extraction zone to thereby prevent positive ions from migrating from the ionizing zone to the extraction zone. Low-energy electrons, which would ordinarily be dragged by the positive ions into the extraction zone, are thereby prevented from being present in the extraction zone and being extracted along with negative ions by the extraction grid. Additional electrons are suppressed from the output flux using ExB drift provided by permanent magnets and the extractor grid electrical field.

Leung, K.N.; Ehlers, K.W.

1982-08-06

227

Chemical composition of lipids present in cat and dog oocyte by matrix-assisted desorption ionization mass spectrometry (MALDI- MS).  

PubMed

The aim of the present study was to investigate the level of information on the chemical structures and relative abundances of lipids present in cat and dog oocytes by matrix-assisted laser desorption mass spectrometry (MALDI-MS). The MALDI-MS approach requires a simple analysis workflow (no lipid extraction) and few samples (two or three oocytes per analysis in this work) providing concomitant profiles of both intact phospholipids such as sphingomyelins (SM) and phosphatidylcholines (PC) as well as triacylglycerols (TAG). The lipids were detected in oocytes by MALDI using dihydroxybenzoic acid (DHB) as the matrix. The most abundant lipid present in the MS profiles of bitch and queen oocytes was a PC containing 34 carbons and one unsaturation [PC (34:1)]. Oocytes of these two species are characterized by differences in PC and TAG profiles detected qualitatively as well as by means of principal component analysis (PCA). Cat oocytes were mainly discriminated by more intense C52 and C54 TAG species and a higher number of unsaturations, indicating predominantly linoleic and oleic fatty acyl residues. Comparison of the lipid profile of bitch and queen oocytes with that of bovine oocytes revealed some similarities and also some species specificity: TAG species present in bovine oocytes were also present in bitches and queens; however, a more pronounced contribution of palmitic, stearic and oleic fatty acid residues was noticed in the lipid profile of bovine oocytes. MALDI-MS provides novel information on chemical lipid composition in canine and feline oocytes, offering a suitable tool to concomitantly monitor, in a nearly direct and simple fashion the composition of phospholipids and TAG. This detailed information is highly needed to the development of improved protocols for in vitro culture and cryopreservation of cat and dog oocytes. PMID:23279478

Apparicio, M; Ferreira, C R; Tata, A; Santos, V G; Alves, A E; Mostachio, G Q; Pires-Butler, E A; Motheo, T F; Padilha, L C; Pilau, E J; Gozzo, F C; Eberlin, M N; Lo Turco, E G; Luvoni, G C; Vicente, W R R

2012-12-01

228

Development and validation of a sensitive method for simultaneous determination of rosuvastatin and N-desmethyl rosuvastatin in human plasma using liquid chromatography/negative electrospray ionization/tandem mass spectrometry.  

PubMed

A sensitive and specific liquid chromatography tandem mass spectrometric method was developed and validated for the simultaneous determination of rosuvastatin (ROS) and N-desmethyl rosuvastatin (NOR-ROS) in human plasma using deuterium-labeled internal standards. The plasma samples were prepared using liquid-liquid extraction with diethyl ether. Chromatographic separation was accomplished on an Xterra MS C18 column. The mobile phase consisted of a gradient mixture of 15?µmol/L ammonium acetate in water and in methanol, maintained at a flow rate of 0.4?mL/min. Mass spectrometric detection was carried out in negative electrospray ionization mode and monitored by quantification and qualification transitions for each analyte. Using 300 ?L plasma samples, the lower limits of quantification of ROS and NOR-ROS were 0.05 and 0.02?µg/L respectively. The linearity of ROS and NOR-ROS ranged from 0.05 to 42 and 0.02 to 14?µg/L respectively. The relative standard deviations of ROS and NOR-ROS were <13 and 9%, respectively, while the deviations from expected values were within -4.7-9.8 and -5.2-4.6%, respectively. The present method offered high sensitivity and was successfully applied to a 24?h pharmacokinetic study of ROS and NOR-ROS in healthy subjects receiving a single dose of 10?mg ROS. PMID:23722358

Lee, H K; Ho, C S; Hu, M; Tomlinson, B; Wong, C K

2013-11-01

229

Sensitive determination of RDX, nitroso-RDX metabolites, and other munitions in ground water by solid-phase extraction and isotope dilution liquid chromatography–atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

Recent improvements in the LC–MS interface have increased the sensitivity and selectivity of this instrument in the analysis of polar and thermally-labile aqueous constituents. Determination of RDX, nitroso-RDX metabolites, and other munitions was enhanced using LC–MS with solid-phase extraction, 15N3-RDX internal standard, and electrospray ionization (ESI) in negative ion mode. ESI produced a five-fold increase in detector response over atmospheric

D. A. Cassada; S. J. Monson; D. D. Snow; R. F. Spalding

1999-01-01

230

Secondary ion counting for surface-sensitive chemical analysis of organic compounds using time-of-flight secondary ion mass spectroscopy with cluster ion impact ionization  

SciTech Connect

We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C{sub 8} and C{sub 60} cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.

Hirata, K. [National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 (Japan); Saitoh, Y.; Chiba, A.; Yamada, K. [Takasaki Advanced Radiation Research Institute (TARRI), Japan Atomic Energy Agency (JAEA), Takasaki Gumma 370-1292 (Japan); Takahashi, Y.; Narumi, K. [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Takasaki, Gumma 370-1292 (Japan)

2011-03-15

231

Analysis of cocaine and its metabolites from biological specimens using solid-phase extraction and positive ion chemical ionization mass spectrometry.  

PubMed

An accurate and reliable gas chromatographic-mass spectrometric method was developed to analyze tissue, whole blood, plasma, and urine samples for cocaine (COC) and its major metabolites. COC, benzoylecgonine (BZE), and ecgonine methyl ester (EME) were isolated from the biological matrix using solid-phase extraction, and the tert-butyldimethylsilyl derivatives of BZE, EME, and their deuterium-labeled internal standards were formed. Separation of the compounds was performed by capillary chromatography, and analysis was performed by positive ion chemical ionization mass spectrometry using methane and ammonia as the reagent gases. The tert-butyldimethylsilyl derivatives of BZE and EME were stable and produced mass spectral ions with higher mass-to-charge ratios than trimethylsilyl derivatives. Recovery of COC and its metabolites exceeded 80% at all three concentrations tested. Linearity of the method was established from 2.5 to 2000 microg/L. Intra-assay precision had a coefficient of variation (CV) of less than 9% for all analytes when tested at 10, 25, 100, and 200 microg/L. Interassay precision also had a CV of less than 9% for COC, BZE, and EME at 25 and 100 microg/L. At 200 microg/L, %CVs for COC, BZE, and EME were 11.5, 12.0, and 12.7, respectively. In addition to the analysis of COC, BZE, and EME, the method was used to quantitate cocaethylene and to identify norcocaine. PMID:8926728

Crouch, D J; Alburges, M E; Spanbauer, A C; Rollins, D E; Moody, D E

1995-10-01

232

Chemical separation and mass spectrometry of Cr, Fe, Ni, Zn, and Cu in terrestrial and extraterrestrial materials using thermal ionization mass spectrometry.  

PubMed

A sequential chemical separation technique for Cr, Fe, Ni, Zn, and Cu in terrestrial and extraterrestrial silicate rocks was developed for precise and accurate determination of elemental concentration by the isotope dilution method (ID). The technique uses a combination of cation-anion exchange chromatography and Eichrom nickel specific resin. The method was tested using a variety of matrixes including bulk meteorite (Allende), terrestrial peridotite (JP-1), and basalt (JB-1b). Concentrations of each element was determined by thermal ionization mass spectrometry (TIMS) using W filaments and a Si-B-Al type activator for Cr, Fe, Ni, and Zn and a Re filament and silicic acid-H3PO4 activator for Cu. The method can be used to precisely determine the concentrations of these elements in very small silicate samples, including meteorites, geochemical reference samples, and mineral standards for microprobe analysis. Furthermore, the Cr mass spectrometry procedure developed in this study can be extended to determine the isotopic ratios of 53Cr/52Cr and 54Cr/52Cr with precision of approximately 0.05epsilon and approximately 0.10epsilon (1epsilon = 0.01%), respectively, enabling cosmochemical applications such as high precision Mn-Cr chronology and investigation of nucleosynthetic isotopic anomalies in meteorites. PMID:19886654

Yamakawa, Akane; Yamashita, Katsuyuki; Makishima, Akio; Nakamura, Eizo

2009-12-01

233

Analysis of 1,2-diol diesters in vernix caseosa by high-performance liquid chromatography - atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Fatty acid diesters of long-chain 1,2-diols (1,2-DDE), or type II wax diesters, were analyzed in the vernix caseosa of a newborn girl. 1,2-DDE were isolated from the total lipid extract by the semipreparative TLC using plates coated with silica gel. Chromatographic separation of the 1,2-DDE molecular species was achieved on the non-aqueous reversed-phase HPLC with two Nova-Pak C18 columns connected in series (a total length of 45cm) and using an acetonitrile-ethyl acetate gradient. 1,2-DDE eluted from the column in the order of their equivalent chain number. The analytes were detected as ammonium adducts by an ion-trap mass spectrometer equipped with an atmospheric pressure chemical ionization source. Their structures were elucidated using tandem mass spectrometry with MS, MS(2) and MS(3) steps in a data-dependent mode. More than two thousand molecular species of 1,2-DDE were identified in 141 chromatographic peaks. The most abundant 1,2-DDE were monounsaturated lipids consisting of a C22 diol and a C18:1 fatty acid together with C16:0, C14:0 or C15:0 fatty acids. The positions of double bonds were characterized by the fragmentation of [M+C3H5N](+) formed in the ion source. PMID:25555408

Šub?íková, Lenka; Hoskovec, Michal; Vrkoslav, Vladimír; ?melíková, Tereza; Háková, Eva; Míková, Radka; Coufal, Pavel; Doležal, Antonín; Plavka, Richard; Cva?ka, Josef

2015-01-23

234

Characterization of cis-9 trans-11 trans-15 C18:3 in milk fat by GC and covalent adduct chemical ionization tandem MS.  

PubMed

Rumen biohydrogenation of dietary alpha-linolenic acid gives rise in ruminants to accumulation of fatty acid intermediates, some of which may be transferred into milk. Rumelenic acid [cis-9 trans-11 cis-15 C18:3 (RLnA)] has recently been characterized, but other C18:3 minor isomers are still unknown. The objective of this work was to identify a new isomer of octatridecenoic acid present in milk fat from ewes fed different sources of alpha-linolenic acid. Structural characterization of this fatty acid was achieved by GC-MS. Analysis of dimethyloxazoline and picolinyl ester derivatives allowed for location of the double bond positions. Covalent adduct chemical ionization tandem mass spectrometry confirmed the positional structure 9-11-15, identical to RLnA, and helped to establish double bond geometry (cis-trans-trans). This new C18:3 isomer could be formed by isomerization of cis-15 bond of RLnA and subsequently converted by hydrogenation to trans-11 trans-15 C18:2, an octadecadienoic acid also detected in this study. PMID:19542528

Gómez-Cortés, Pilar; Tyburczy, Cynthia; Brenna, J Thomas; Juárez, Manuela; de la Fuente, Miguel Angel

2009-12-01

235

Quantitation of the 5HT1D agonists MK-462 and sumatriptan in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

The 5HT1D agonist sumatriptan is efficacious in the treatment of migraines. MK-462 is a drug of the same class which is under development in our laboratories. Bioanalytical methods of high efficiency, specificity and sensitivity were required to support the preclinical and clinical programs. These assays were based on HPLC with tandem MS-MS detection. MK-462 and sumatriptan were extracted using an automated solid-phase extraction technique on a C2 Varian Bond-Elut cartridge. The n-diethyl analogues of MK-462 and sumatriptan were used as internal standards. The analytes were chromatographed using reversed-phase (nitrile) columns coupled via a heated nebulizer interface to an atmospheric pressure chemical ionization source. The chromatographic run times were less than 7 min. Both methods were precise, accurate and selective down to plasma concentrations of 0.5 ng/ml. The assay for MK-462 was adapted to separately monitor the unlabeled and 14C-labeled species of the drug following intravenous administration of radiolabeled material to man. PMID:8900521

McLoughlin, D A; Olah, T V; Ellis, J D; Gilbert, J D; Halpin, R A

1996-03-01

236

Characterization of cis-9 trans-11 trans-15 C18:3 in milk fat by GC and covalent adduct chemical ionization tandem MS  

PubMed Central

Rumen biohydrogenation of dietary ?-linolenic acid gives rise in ruminants to accumulation of fatty acid intermediates, some of which may be transferred into milk. Rumelenic acid [cis-9 trans-11 cis-15 C18:3 (RLnA)] has recently been characterized, but other C18:3 minor isomers are still unknown. The objective of this work was to identify a new isomer of octatridecenoic acid present in milk fat from ewes fed different sources of ?-linolenic acid. Structural characterization of this fatty acid was achieved by GC-MS. Analysis of dimethyloxazoline and picolinyl ester derivatives allowed for location of the double bond positions. Covalent adduct chemical ionization tandem mass spectrometry confirmed the positional structure 9-11-15, identical to RLnA, and helped to establish double bond geometry (cis-trans-trans). This new C18:3 isomer could be formed by isomerization of cis-15 bond of RLnA and subsequently converted by hydrogenation to trans-11 trans-15 C18:2, an octadecadienoic acid also detected in this study. PMID:19542528

Gómez-Cortés, Pilar; Tyburczy, Cynthia; Brenna, J. Thomas; Juárez, Manuela; de la Fuente, Miguel Angel

2009-01-01

237

Identification and quantification of antitumor thioproline and methylthioproline in Korean traditional foods by a liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

A liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometric method (LC-APCI-MS/MS) has been developed for the sensitive determination of antitumor thioproline and methylthioproline from fermented foods. Thioproline and methylthioproline were derivatized in one step with ethyl chloroformate at room temperature. These compounds were identified and quantified in various traditional Korean fermented foods by LC-APCI-MS/MS. The concentration range of thioproline of each food was found for doenjang (0.011-0.032mg/kg), gochujang (0.010-0.038mg/kg), and ganjang (0.010-0.038mg/kg). Those of methylthioproline of each food was found for doenjang (0.098-0.632mg/kg), gochujang (0.015-0.112mg/kg), and ganjang (0.023-1.468mg/kg). A prolonged aging time leads to an increase in both the thioproline and methylthioproline contents, suggesting that the storage time plays a key role in the formation of thioproline and methylthioproline in Korean traditional foods. The results here suggest that thioproline and methylthioproline are related to the biological activities of traditional Korean fermented foods. PMID:25128876

Kim, Sun Hyo; Kim, Hyun-Ji; Shin, Ho-Sang

2014-11-01

238

Molecular negative surface ionization of UF6  

Microsoft Academic Search

Investigations have been carried out to elucidate the process of formation of UF6? molecular ions on heated surfaces. On a carbon coated Pt surface the absolute efficiency of conversion of UF6 to UF6? was found to be 99+1?5% over a wide temperature range in accordance with anticipations based solely on measured thermionic work functions and the molecular electron affinity of

P. F. Dittner; S. Datz

1978-01-01

239

Molecular Characterization of S- and N-containing Organic Constituents in Ambient Aerosols by negative ion mode High-Resolution Nanospray Desorption Electrospray Ionization Mass Spectrometry: CalNex 2010 field study  

SciTech Connect

Samples of ambient aerosols from the 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study were analyzed using Nanospray Desorption Electrospray Ionization High Resolution Mass Spectrometry (nano-DESI/MS). Four samples per day were collected in Bakersfield, CA on June 20-24 with a collection time of 6 hours per sample. Four characteristic groups of organic constituents were identified in the samples: compounds containing carbon, hydrogen, and oxygen only (CHO), sulfur- (CHOS), nitrogen-(CHON), and both nitrogen- and sulfur-containing organics (CHONS). Within the groups, organonitrates, organosulfates, and nitroxy organosulfates were assigned based on accurate mass measurements and elemental ratio comparisons. Changes in the chemical composition of the aerosol samples were observed throughout the day. The number of observed CHO compounds increased in the afternoon samples, suggesting regional photochemical processing as a source. The average number of CHOS compounds had the smallest changes throughout the day, consistent with a more broadly distributed source. Both of the nitrogen-containing groups (CHON and CHONS) had greater numbers of compounds in the night and morning samples, indicating that nitrate radical chemistry was likely a source for those compounds. Most of the compounds were found in submicron particles. The size distribution of CHON compounds was bimodal. We conclude that the majority of the compounds observed were secondary in nature with both biogenic and anthropogenic sources.

O'Brien, Rachel E.; Laskin, Alexander; Laskin, Julia; Rubitschun, Caitlin L.; Surratt, Jason D.; Goldstein, Allen H.

2014-11-19

240

Determination of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls by gas chromatography/mass spectrometry in the negative chemical ionization mode with different reagent gases.  

PubMed

Reagent gases that are used in mass spectrometry in the NCI mode for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) are discussed. Ion-molecule reactions and respective characteristic ions that form while using reagent gases (CH(4), O(2), i-C(4)H(10), NH(3), H(2), He, Ar, Xe, SF(6)) or gas mixtures (CH(4)/O(2), Ar/CH(4), CH(4)/H(2)O, Ar/O(2), i-C(4)H(10)/CH(2)Cl(2)/O(2)) are reviewed. It is shown that only CH(4), O(2), CH(4)/O(2), and CH(4)/N(2)O are widely used and well studied, even though-in the case of these reagent gases-there are contradictions between the publications of various authors. Such reagent gases as NH(3) and He are not well studied, but further investigations of their use for the determination of organochlorine pollutants could be of interest. The possibilities of more sensitive and selective determination of PCDDs, PCDFs, and PCBs are discussed. PMID:12666147

Chernetsova, Elena S; Revelsky, Alexander I; Revelsky, Igor A; Mikhasenko, Ilya A; Sobolevsky, Tim G

2002-01-01

241

Gridded electron reversal ionizer  

NASA Technical Reports Server (NTRS)

A gridded electron reversal ionizer forms a three dimensional cloud of zero or near-zero energy electrons in a cavity within a filament structure surrounding a central electrode having holes through which the sample gas, at reduced pressure, enters an elongated reversal volume. The resultant negative ion stream is applied to a mass analyzer. The reduced electron and ion space-charge limitations of this configuration enhances detection sensitivity for material to be detected by electron attachment, such as narcotic and explosive vapors. Positive ions may be generated by generating electrons having a higher energy, sufficient to ionize the target gas and pulsing the grid negative to stop the electron flow and pulsing the extraction aperture positive to draw out the positive ions.

Chutjian, Ara (Inventor)

1993-01-01

242

Harnessing entropic and enthalpic contributions to create a negative tone chemically amplified molecular resist for high-resolution lithography  

NASA Astrophysics Data System (ADS)

Here we present a new resist design concept. By adding dilute cross-linkers to a chemically amplified molecular resist, we synergize entropic and enthalpic contributions to dissolution by harnessing both changes to molecular weight and changes in intermolecular bonding to create a system that outperforms resists that emphasize one contribution over the other. We study patterning performance, resist modulus, solubility kinetics and material redistribution as a function of cross-linker concentration. Cross-linking varies from dilute oligomerization to creating a highly networked system. The addition of small amounts of cross-linker improves resist performance by reducing material diffusion and redistribution during development and stiffening the features to avoid pattern collapse. The new dilute cross-linking system achieves the highest resolution of a sensitive molecular glass resist at 20 nm half-pitch and line-edge roughness (LER) of 4.3 nm and can inform new resist design towards patterned feature control at the molecular level.

Kulshreshtha, Prashant K.; Maruyama, Ken; Kiani, Sara; Blackwell, James; Olynick, Deirdre L.; Ashby, Paul D.

2014-08-01

243

Separation and detection of compounds in Honeysuckle by integration of ion-exchange chromatography fractionation with reversed-phase liquid chromatography-atmospheric pressure chemical ionization mass spectrometer and matrix-assisted laser desorption\\/ionization time-of-flight mass spectrometry analysis  

Microsoft Academic Search

A hyphenated method for the isolation and identification of components in a traditional Chinese medicine of Honeysuckle was developed. Ion-exchange chromatography (IEC) was chosen for the fractionation of Honeysuckle extract, and then followed by concentration of all the fractions with rotary vacuum evaporator. Each of the enriched fractions was then further analyzed by reversed-phase liquid chromatography-atmospheric pressure chemical ionization mass

Xueguo Chen; Lianghai Hu; Xingye Su; Liang Kong; Mingliang Ye; Hanfa Zou

2006-01-01

244

Sensitivity improvement in hydrophilic interaction chromatography negative mode electrospray ionization mass spectrometry using 2-(2-methoxyethoxy)ethanol as a post-column modifier for non-targeted metabolomics.  

PubMed

The application of ammonia acetate buffered liquid chromatography (LC) eluents is known to concomitantly lead to ion suppression when electrospray ionization mass spectrometry (ESI-MS) detection is used. In negative ESI mode, post column infusion of 2-(2-methoxyethoxy)ethanol (2-MEE) was shown in the literature to help to compensate this adverse effect occurring in reversed phase liquid chromatography mass spectrometry (RP-LC-MS) analyses. Here a setup of direct infusion and hydrophilic interaction chromatography (HILIC) post-column infusion experiments was established in order to investigate systematically the beneficial effects of 2-MEE. We demonstrate that, 2-MEE can help to improve ESI-MS sensitivity in HILIC too and reveal analyte structure specific behaviors. Our study indicates that 2-MEE especially improves ESI response for small and polar molecules. The ESI response of stable isotope labeled amino acids spiked into biological matrices increases up to 50-fold (i.e. D5-l-glutamic acid) when post column infusion of 2-MEE is applied. A non-targeted analysis of a pooled urine sample via HILIC-ESI-QTOF-MS supports this hypothesis. In direct infusion, the combined application of an ammonia acetate buffered solution together with 2-MEE results in an improved ESI response compared to a non-buffered solution. We observed up to 60-fold increased ESI response of l-lysine. We propose this effect is putatively caused by the formation of smaller ESI droplets and stripping of positive charge from ESI droplets due to evaporation of acetic acid anions. In summary, post-column infusion of 2-MEE especially enhances ESI response of small and polar molecules. Therefore it can be regarded as a valuable add-on in targeted or non-targeted metabolomic HILIC-MS studies since this method sets a focus on this molecule category. PMID:25160955

Koch, Wendelin; Forcisi, Sara; Lehmann, Rainer; Schmitt-Kopplin, Philippe

2014-09-26

245

Differentiation of Positional Isomers of Hybrid Peptides Containing Repeats of ?-Nucleoside Derived Amino Acid (?-Nda-) and L-Amino Acids by Positive and Negative Ion Electrospray Ionization Tandem Mass Spectrometry (ESI-MS n )  

NASA Astrophysics Data System (ADS)

A new class of positional isomeric pairs of -Boc protected oligopeptides comprised of alternating nucleoside derived ?-amino acid (?-Nda-) and L-amino acid residues (alanine, valine, and phenylalanine) have been differentiated by both positive and negative ion electrospray ionization ion-trap tandem mass spectrometry (ESI-MS n ). The protonated dipeptide positional isomers with ?-Nda- at the N-terminus lose CH3OH, NH3, and C2H4O2, whereas these processes are absent for the peptides with L-amino acids at the N-terminus. Instead, the presence of L-amino acids at the N-terminus results in characteristic retro-Mannich reaction involving elimination of imine. A good correlation has been observed between the conformational structure of the peptides and the abundance of y{n/+} and b{n/+} ions in MS n spectra. In the case of tetrapeptide isomers that are reported to form helical structures in solution phase, no y{n/+} and b{n/+} ions are observed when the corresponding amide -NH- participates in the helical structures. In contrast, significant y{n/+} and b{n/+} ions are formed when the amide -NH- is not involved in the H-bonding. In the case of tetra- and hexapeptides, it is observed that abundant b{n/+} ions are formed, presumably with stable oxazolone structures when the C-terminus of the b{n/+} ions possessed L-amino acid and the ?-Nda- at the C-terminus appears to prevent the cyclization process leading to the absence of corresponding b{n/+} ions.

Raju, B.; Ramesh, M.; Srinivas, R.; Chandrasekhar, S.; Kiranmai, N.; Sarma, V. U. M.

2011-04-01

246

pH-dependent random coil (1)H, (13)C, and (15)N chemical shifts of the ionizable amino acids: a guide for protein pK a measurements.  

PubMed

The pK a values and charge states of ionizable residues in polypeptides and proteins are frequently determined via NMR-monitored pH titrations. To aid the interpretation of the resulting titration data, we have measured the pH-dependent chemical shifts of nearly all the (1)H, (13)C, and (15)N nuclei in the seven common ionizable amino acids (X = Asp, Glu, His, Cys, Tyr, Lys, and Arg) within the context of a blocked tripeptide, acetyl-Gly-X-Gly-amide. Alanine amide and N-acetyl alanine were used as models of the N- and C-termini, respectively. Together, this study provides an essentially complete set of pH-dependent intra-residue and nearest-neighbor reference chemical shifts to help guide protein pK a measurements. These data should also facilitate pH-dependent corrections in algorithms used to predict the chemical shifts of random coil polypeptides. In parallel, deuterium isotope shifts for the side chain (15)N nuclei of His, Lys, and Arg in their positively-charged and neutral states were also measured. Along with previously published results for Asp, Glu, Cys, and Tyr, these deuterium isotope shifts can provide complementary experimental evidence for defining the ionization states of protein residues. PMID:25239571

Platzer, Gerald; Okon, Mark; McIntosh, Lawrence P

2014-11-01

247

Harnessing entropic and enthalpic contributions to create a negative tone chemically amplified molecular resist for high-resolution lithography.  

PubMed

Here we present a new resist design concept. By adding dilute cross-linkers to a chemically amplified molecular resist, we synergize entropic and enthalpic contributions to dissolution by harnessing both changes to molecular weight and changes in intermolecular bonding to create a system that outperforms resists that emphasize one contribution over the other. We study patterning performance, resist modulus, solubility kinetics and material redistribution as a function of cross-linker concentration. Cross-linking varies from dilute oligomerization to creating a highly networked system. The addition of small amounts of cross-linker improves resist performance by reducing material diffusion and redistribution during development and stiffening the features to avoid pattern collapse. The new dilute cross-linking system achieves the highest resolution of a sensitive molecular glass resist at 20 nm half-pitch and line-edge roughness (LER) of 4.3 nm and can inform new resist design towards patterned feature control at the molecular level. PMID:25026410

Kulshreshtha, Prashant K; Maruyama, Ken; Kiani, Sara; Blackwell, James; Olynick, Deirdre L; Ashby, Paul D

2014-08-01

248

Determination of melamine and cyanuric acid in powdered milk using injection-port derivatization and gas chromatography-tandem mass spectrometry with furan chemical ionization.  

PubMed

A reliable, sensitive and eco-friendly injection-port trimethylsilylated (TMS) derivatization and gas chromatography-tandem mass spectrometry (GC-MS/MS) with furan chemical ionization (furan-CI) method was developed to determine melamine and cyanuric acid in powdered milk samples. The effects of several parameters related to the TMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) and of various CI agents were investigated. Addition of a solution (3 ?L) of bis(trimethyl)silyltrifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane (TMCS) reagent to a 20-?L extract from the powdered milk sample gave an excellent yield of the tris-TMS-derivatives of melamine and cyanuric acid at an injection-port temperature of 90°C. Furthermore, using furan as the CI agent in conjunction with tandem mass spectrometry provided the greatest sensitivity and selectivity of detection. The limits of quantitation (LOQs) for melamine and cyanuric acid were 0.5 and 1.0 ng/g in 0.5-g of powdered milk samples, respectively. The recoveries from spiked samples--after simple ultra-sonication with 5% dimethyl sulfoxide in acetonitrile coupled with n-hexane liquid-liquid extraction--ranged from 72% to 93% with relative standard deviations of lower than or equal to 18%. In three of four real powdered milk samples, melamine was detected at concentrations ranging from 36 to 1460 ng/g; and cyanuric acid was detected in two of these samples at concentrations of 17 and 180 ng/g. PMID:20800234

Tzing, Shin-Hwa; Ding, Wang-Hsien

2010-10-01

249

Measurements of Oxidized Organic Compounds during SOAS 2013 using nitrate ion chemical ionization coupled with High Resolution Time-of-Flight Mass Spectrometry  

NASA Astrophysics Data System (ADS)

We present ambient measurements of gaseous organic compounds by means of a High Resolution Time-of-Flight Chemical Ionization Mass Spectrometry (HR-ToF-CIMS) using nitrate ion (NO3-) chemistry. This technique allows to selectively detect oxidized gas-phase species, e.g., oxidized organic molecules and sulfuric acid via clustering with NO3- and its high order clusters. The capability of making such measurements is important because both sulfuric acid and organic gas molecules have a recognized key role in new particle formation (NPF) processes and likely have an important role in particulate phase chemistry and formation of secondary organic aerosols (SOA). The HR-ToF-CIMS was deployed during the Southern Oxidant and Aerosol Study (SOAS) at the forest supersite in Centreville, AL, from June 1 to July 15, 2013. The main goal of the SOAS campaign was to investigate the composition and sources of SOA in the Southeast US, where emissions are mainly represented by biogenic volatile organic compounds (BVOC) emissions and in less extent by anthropogenic emissions (AVOC). During SOAS, the HR-ToF-CIMS detected a range of organic ions that based on previous literature could be identified as oxidation products of both isoprene and terpenes. The isoprene products were 5 to 10 times more abundant than the terpene products. The isoprene-related molecules showed a diurnal cycle with a day time peak, typically after 1500 local time, while the terpene products were higher at night (between 2000 and 0600 local time). These results are consistent with the diurnal trends of primary BVOC emissions from other co-located instruments. The ambient data are also compared to laboratory measurements where oxidized organic vapors are produced using a Potential Aerosol Mass (PAM) flow reactor by the OH oxidation of biogenic gas-phase precursors (isoprene, a-pinene) over multiple days of equivalent atmospheric exposure.

Massoli, P.; Stark, H.; Cnagaratna, M.; Junninen, H.; Hakala, J. P.; Mauldin, R.; Ehn, M.; Sipila, M.; Krechmer, J.; Kimmel, J.; Jimenez, J. L.; Jayne, J. T.; Worsnop, D. R.

2013-12-01

250

Development of An Ion-Drift Time-of-Flight Chemical Ionization Mass Spectrometry Technique for Measurements of Aerosol Precursor Gases  

NASA Astrophysics Data System (ADS)

We have developed a new technique, i.e., ion-drift time-of-flight chemical ionization mass spectrometry (ID-ToF-CIMS) for measurements of aerosol precursor gases, including ammonia, amines, organic acids and oxygenated VOCs at pptv level with a response time less than 1 s. The ID-ToF-CIMS was modified from an Aerodyne high resolution ToF-CIMS with a custom-designed ion-drift tube, which can control the ion flight velocity and hence the ion-molecular reaction time. In addition, the tunable electric field generated by the drift tube can break up water clusters to select the major reagent ions. The advantages of the ID-ToF-CIMS over the traditional quadrupole-based ID-CIMS were the high mass-resolving power of the ToF mass analyzer and the capability of simultaneous measurement of the full mass range (typically up to 300 m/z) of product ions. Using hydronium ion based reagent ions, we demonstrated that the ID-ToF-CIMS can unambiguously measure ammonia (NH3) at 18.03 m/z, methyl amine (CH3NH2) at 32.05 m/z, formic acid (HCOOH) at 47.01 m/z and acetone (CH3COCH3) at 59.05 m/z. Calibrations were performed with both compressed commercial standard gases and permeation tubes and the results showed that the instrument detection limit can reach pptv level for 1 s average time or less. The ID-ToF-CIMS was also field tested in a mobile laboratory on the campus of Nanjing University of Information Science & Technology (NUIST). The preliminary results will be discussed.

Zheng, J.; Ma, Y.; Chen, M.

2012-12-01

251

Profiling of triacylglycerols in plant oils by high-performance liquid chromatography-atmosphere pressure chemical ionization mass spectrometry using a novel mixed-mode column.  

PubMed

In this investigation, a rapid and high-throughput method for profiling of TAGs in plant oils by liquid chromatography using a single column coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry was reported. A novel mixed-mode phenyl-hexyl chromatographic column was employed in this separation system. The phenyl-hexyl column could provide hydrophobic interactions as well as ?-? interactions. Compared with two traditionally columns used in TAG separation - the C18 column and silver-ion column, this column exhibited much higher selectivity for the separation of TAGs with great efficiency and rapid speed. By comparison with a novel mix-mode column (Ag-HiSep OTS column), which can also provide both hydrophobic interactions as well as ?-? interactions for the separation of TAGs, phenyl-hexyl column exhibited excellent stability. LC method using phenyl-hexyl column coupled with APCI-MS was successfully applied for the profiling of TAGs in soybean oils, peanut oils, corn oils, and sesame oils. 29 TAGs in peanut oils, 22 TAGs in soybean oils, 19 TAGs in corn oils, and 19 TAGs in sesame oils were determined and quantified. The LC-MS data was analyzed by barcodes and principal component analysis (PCA). The resulting barcodes constitute a simple tool to display differences between different plant oils. Results of PCA also enabled a clear identification of different plant oils. This method provided an efficient and convenient chromatographic technology for the fast characterization and quantification of complex TAGs in plant oils at high selectivity. It has great potential as a routine analytical method for analysis of edible oil quality and authenticity control. PMID:25444539

Hu, Na; Wei, Fang; Lv, Xin; Wu, Lin; Dong, Xu-Yan; Chen, Hong

2014-12-01

252

Investigating the potential of high-performance liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry as an alternative method for the speciation analysis of organotin compounds.  

PubMed

Liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was applied for the determination of butyl- and phenyltin compounds. Chromatography was performed on a 30 x 2 mm, 3 microm C18 column, enabling the separation of mono-, di- and trisubstituted butyl- and phenyltin compounds in less than 10 min using a water/1% trifluoroacetic acid/methanol gradient. While satisfactory retention and resolution is achieved for the di- and trisubstituted butyl- and phenyltin compounds, monobutyltin and monophenyltin cannot be resolved chromatographically. Depending on the parameter values of the interface, APCI-MS detection allows both specific detection of the molecular ion or cluster ion at low to intermediate fragmentor voltages or quasi-element specific detection of the Sn+ ion released from the organotin compounds at high fragmentor voltages. The sensitivity of MS detection is similar for butyl- and phenyltin compounds, but varies largely from mono- to trisubstituted organotin compounds with tributyl- and triphenyltin being the most sensitively detectable compounds. Detection limits are in the 20-65 pg (abs.) range in SIM mode and in the 750-2000 pg (abs.) range in the scan mode for tributyl- and triphenyltin and for dibutyl- and diphenyltin, respectively. Monobutyl- and monophenyltin can be detected with much lower sensitivity which, together with their unfavorable chromatographic behavior, accounts for the fact that they cannot be analyzed at environmentally relevant concentrations. Although LC-APCI-MS is generally less sensitive than comparable GC methods, it is applicable to the analysis of environmental samples as demonstrated by the analysis of the PACS-2 sediment certified reference material. Although the derivatization of the ionic organotin compounds, which particularly in real samples is a potential source of error, is circumvented when LC-APCI-MS is used, the extraction step is still critical and may lead to underestimation when quantitation is not done by the method of standard addition. PMID:11220328

Rosenberg, E; Kmetov, V; Grasserbauer, M

2000-02-01

253

Validation of a qualitative screening method for pesticides in fruits and vegetables by gas chromatography quadrupole-time of flight mass spectrometry with atmospheric pressure chemical ionization.  

PubMed

A wide-scope screening method was developed for the detection of pesticides in fruit and vegetables. The method was based on gas chromatography coupled to a hybrid quadrupole time-of-flight mass spectrometer with an atmospheric pressure chemical ionization source (GC-(APCI)QTOF MS). A non-target acquisition was performed through two alternating scan events: one at low collision energy and another at a higher collision energy ramp (MS(E)). In this way, both protonated molecule and/or molecular ion together with fragment ions were obtained in a single run. Validation was performed according to SANCO/12571/2013 by analysing 20 samples (10 different commodities in duplicate), fortified with a test set of 132 pesticides at 0.01, 0.05 and 0.20mg kg(-1). For screening, the detection was based on one diagnostic ion (in most cases the protonated molecule). Overall, at the 0.01mg kg(-1) level, 89% of the 2620 fortifications made were detected. The screening detection limit for individual pesticides was 0.01mg kg(-1) for 77% of the pesticides investigated. The possibilities for identification according to the SANCO criteria, requiring two ions with a mass accuracy ?±5ppm and an ion-ratio deviation ?±30%, were investigated. At the 0.01mg kg(-1) level, identification was possible for 70% of the pesticides detected during screening. This increased to 87% and 93% at the 0.05 and 0.20mg kg(-1) level, respectively. Insufficient sensitivity for the second ion was the main reason for the inability to identify detected pesticides, followed by deviations in mass accuracy and ion ratios. PMID:25064246

Portolés, T; Mol, J G J; Sancho, J V; López, Francisco J; Hernández, F

2014-08-01

254

High performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry for sensitive determination of bioactive amines in donkey milk.  

PubMed

In the present study we report on the optimization and validation of a sensitive high performance liquid chromatography atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) method for the determination of 8 bioactive amines (histamine, tyramine, tryptamine, 2-phenylethylamine, cadaverine, putrescine, spermidine and spermine) in donkey milk samples. The method involves donkey milk pre-treatment to remove proteins and pre-column dansylation of the amines. HPLC in reversed phase mode has been used for bioactive amines separation and the operating condition of the APCI-MS system proved to be powerful and very efficient for peak assignment. The separation was accomplished in a short time with an excellent resolution for all the amine peaks. Quantification was carried out by monitoring the characteristic [M+H](+) ion of each amine derivative. The method sensitivity, linearity and repeatability were assayed with satisfactory results. The detection limits of the analysed amines ranged from 0.5 microg L(-1) to 15 microg L(-1); the highest LOD was for spermine. Also remarkably good recovery values were obtained; at the lowest spiking level (1 microg L(-1)) the percent mean recoveries ranged from 77.7 to 109.7. Furthermore, as the investigations relate to a complex matrix as donkey milk, suitable studies on matrix effect were performed. Finally, the developed and validated method was applied to analyse 13 donkey milk samples. Among the identified bioactive amines, putrescine, spermine and spermidine proved to be the main amines in donkey milk. Their concentration levels in the present study were lower than the values determined in mature human, cow and sow milk. PMID:20598311

La Torre, Giovanna Loredana; Saitta, Marcello; Giorgia Potortì, Angela; Di Bella, Giuseppa; Dugo, Giacomo

2010-08-01

255

Quantitation of Benzo[a]pyrene Metabolic Profiles in Human Bronchoalveolar H358) Cells by Stable Isotope Dilution Liquid Chromatography-Atmospheric Chemical Ionization Mass Spectrometry  

PubMed Central

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants and are carcinogenic in multiple organs and species. Benzo[a]pyrene (B[a]P) is a representative PAH and has been studied extensively for its carcinogenicity and toxicity. B[a]P itself is chemically inert and requires metabolic activation to exhibit its toxicity and carcinogenicity. Three major metabolic pathways have been well documented. The signature metabolites generated from the radical cation (peroxidase or monooxygenase mediated) pathway are B[a]P-1,6-dione and B[a]P-3,6-dione, the signature metabolite generated from the diol-epoxide (P450 mediated) pathway is B[a]P-r-7,t-8,t-9,c-10-tetrahydrotetrol (B[a]P-tetrol-1) and the signature metabolite generated from the o-quinone (aldo-keto reductase mediated) pathway is B[a]P-7,8-dione. The contributions of these different metabolic pathways to cancer initiation and the exploitation of this information for cancer prevention are still under debate. With the availability of a library of [13C4]-labeled B[a]P metabolite internal standards, we developed a sensitive stable isotope dilution atmospheric pressure chemical ionization tandem mass spectrometry method to address this issue by quantitating B[a]P metabolites from each metabolic pathway in human lung cells. This analytical method represents a 500 fold increased sensitivity compared with a method using HPLC-radiometric detection. The limit of quantitation (LOQ) was determined to be 6 fmol on column for 3-hydroxybenzo[a]pyrene (3-OH-B[a]P), the generally accepted biomarker for B[a]P exposure. This high level of sensitivity and robustness of the method was demonstrated in a study of B[a]P metabolic profiles in human bronchoalveolar H358 cells induced or uninduced with the AhR ligand, 2,3,7,8-tetrachlorodibenzodioxin (TCDD). All the signature metabolites were detected and successfully quantitated. Our results suggest that all three metabolic pathways contribute equally in the overall metabolism of B[a]P in H358 cells with or without TCDD induction. The sensitivity of the method should permit the identification of cell-type differences in B[a]P activation and detoxication and could also be used for biomonitoring human exposure to PAH. PMID:21962213

Lu, Ding; Harvey, Ronald G.; Blair, Ian A.; Penning, Trevor M.

2013-01-01

256

Results of the negative control chemical allyl alcohol in the 15-day intact adult male rat screening assay for endocrine activity.  

PubMed

Development, standardization, and validation of methods to assess the potential of chemicals to disrupt hormonal homeostasis have been the focus of considerable research efforts over the past 10 years. As part of our validation effort, we evaluated the specificity of the 15-day intact adult male rat assay, using a negative control chemical, allyl alcohol, a known hepatotoxicant that was not expected to induce endocrine effects. Male rats were dosed for 15 days via oral gavage with 0, 10, 30, 40, or 50 mg/kg/day allyl alcohol. The endpoints evaluated included final body and organ weights, serum hormone concentrations, and a limited histopathology assessment. No mortality or adverse clinical signs were observed. Mean final body weight for rats in the 50-mg/kg/day dose group was decreased to 90% of control. Mean relative liver weights were increased at 40 and 50 mg/kg/day (115% and 117% of control, respectively). Serum testosterone and DHT concentrations were statistically significantly decreased at 50 mg/kg/day (72% of control). Serum prolactin concentrations were statistically significantly decreased at 40 mg/kg/day (58% of control), but not at 50 mg/kg/day. There were no effects on the other endpoints evaluated. Consistent with previous guidance for interpreting the 15-day intact adult male rat assay, histological and weight changes of target organs were given a higher weight-of-evidence than changes in serum hormone concentrations alone. Therefore, with only minimal changes in serum hormone concentrations and no effects on organ weights or microscopic alterations, the results of allyl alcohol in the 15-day intact adult male rat assay were considered negative and consistent with the predicted results. PMID:18383315

O'Connor, John C; Marty, M Sue; Becker, Richard A; Snajdr, Suzanne; Kaplan, A Michael

2008-04-01

257

Three chamber negative ion source  

DOEpatents

A negative ion vessel is divided into an excitation chamber, a negative ionization chamber and an extraction chamber by two magnetic filters. Input means introduces neutral molecules into a first chamber where a first electron discharge means vibrationally excites the molecules which migrate to a second chamber. In the second chamber a second electron discharge means ionizes the molecules, producing negative ions which are extracted into or by a third chamber. A first magnetic filter prevents high energy electrons from entering the negative ionization chamber from the excitation chamber. A second magnetic filter prevents high energy electrons from entering the extraction chamber from the negative ionizing chamber. An extraction grid at the end of the negative ion vessel attracts negative ions into the third chamber and accelerates them. Another grid, located adjacent to the extraction grid, carries a small positive voltage in order to inhibit positive ions from migrating into the extraction chamber and contour the plasma potential. Additional electrons can be suppressed from the output flux using ExB forces provided by magnetic field means and the extractor grid electric potential.

Leung, Ka-Ngo (Hercules, CA); Ehlers, Kenneth W. (Alamo, CA); Hiskes, John R. (Livermore, CA)

1985-01-01

258

Degradation of lithium ion batteries employing graphite negatives and nickel-cobalt-manganese oxide + spinel manganese oxide positives: Part 2, chemical-mechanical degradation model  

NASA Astrophysics Data System (ADS)

Capacity fade is reported for 1.5 Ah Li-ion batteries containing a mixture of Li-Ni-Co-Mn oxide (NCM) + Li-Mn oxide spinel (LMO) as positive electrode material and a graphite negative electrode. The batteries were cycled at a wide range of temperatures (10 °C-46 °C) and discharge currents (0.5C-6.5C). The measured capacity losses were fit to a simple physics-based model which calculates lithium inventory loss from two related mechanisms: (1) mechanical degradation at the graphite anode particle surface caused by diffusion-induced stresses (DIS) and (2) chemical degradation caused by lithium loss to continued growth of the solid-electrolyte interphase (SEI). These two mechanisms are coupled because lithium is consumed through SEI formation on newly exposed crack surfaces. The growth of crack surface area is modeled as a fatigue phenomenon due to the cyclic stresses generated by repeated lithium insertion and de-insertion of graphite particles. This coupled chemical-mechanical degradation model is consistent with the observed capacity loss features for the NCM + LMO/graphite cells.

Purewal, Justin; Wang, John; Graetz, Jason; Soukiazian, Souren; Tataria, Harshad; Verbrugge, Mark W.

2014-12-01

259

Photoemission ambient pressure ionization (PAPI) with an ultraviolet light emitting diode and detection of organic compounds.  

PubMed

The development of compact, rugged and low-power ion sources is critical for the further advancement of handheld mass analyzers. Further, there is a need to replace the common (63)Ni source used at atmospheric pressure with a non-radioactive substitute. We present here a description of a light emitting diode (LED) photoemission ionization source for use in mass spectrometry for the detection of volatile organic compounds. This technique relies upon the generation of photoelectrons from a low-work function metal via low-energy ultraviolet (UV) light (280 or 240 nm) generated by a single LED in air at atmospheric pressure. These low-energy photoelectrons result in either direct electron capture by the analyte or chemical ionization. Currently, only negative ions are demonstrated due to operation at atmospheric pressure. Ion generation occurs without use of high electric fields such as those found in corona discharge or electrospray ionization. This source is effective for measuring organic vapors from gases, liquids and surface residues via atmospheric pressure chemical ionization, initiated by photoemission off a conductive surface. Several classes of organic vapors are analyzed and found to be effectively detected, including compounds that ionize via electron attachment, dissociative electron capture, proton abstraction, adduct formation and replacement ionization. PMID:21913267

Short, Luke C; Ewing, Robert G; Barinaga, Charles J

2011-10-15

260

Ionization chamber  

DOEpatents

An ionization chamber has separate drift and detection regions electrically isolated from each other by a fine wire grid. A relatively weak electric field can be maintained in the drift region when the grid and another electrode in the chamber are connected to a high voltage source. A much stronger electric field can be provided in the detection region by connecting wire electrodes therein to another high voltage source. The detection region can thus be operated in a proportional mode when a suitable gas is contained in the chamber. High resolution output pulse waveforms are provided across a resistor connected to the detection region anode, after ionizing radiation enters the drift region and ionize the gas.

Walenta, Albert H. (Port Jefferson Station, NY)

1981-01-01

261

Artifact-Free Quantification of Free 3-Chlorotyrosine, 3-Bromotyrosine, and 3-Nitrotyrosine in Human Plasma by Electron Capture–Negative Chemical Ionization Gas Chromatography Mass Spectrometry and Liquid Chromatography–Electrospray Ionization Tandem Mass Spectrometry  

Microsoft Academic Search

Halogenation and nitration of biomolecules have been proposed as key mechanisms of host defense against bacteria, fungi, and viruses. Reactive oxidants also have the potential to damage host tissue, and they have been implicated in disease. In the current studies, we describe specific, sensitive, and quantitative methods for detecting three stable markers of oxidative damage: 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine. Our

Joseph P. Gaut; Jaeman Byun; Hung D. Tran; Jay W. Heinecke

2002-01-01

262

Measurements of HNO3 and N2O5 using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign  

NASA Astrophysics Data System (ADS)

An ion drift-chemical ionization mass spectrometer (ID-CIMS) was deployed in Mexico City between 7 and 31 March to measure gas-phase nitric acid (HNO3) and dinitrogen pentoxide (N2O5 during the Mexico City Metropolitan Area (MCMA)-2006 field campaign. The observation site was located at the Instituto Mexicano del Petróleo in the northern part of Mexico City urban area with major emissions of pollutants from residential, vehicular and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and early morning. The concentration of HNO3 increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and then declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good agreement between the two HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with submicron-sized aerosol nitrate, suggesting that the gas-particle partitioning process was a major factor in determining the gaseous HNO3 concentration. Losses by irreversible reactions with mineral dust and via dry deposition also could be important at this site. Most of the times during the MCMA 2006 field campaign, N2O5 was found to be below the detection limit (about 30 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio at the surface (>100 ppb) during the night. An exception occurred on 26 March 2006, when about 40 ppt N2O5 was observed during the late afternoon and early evening hours under cloudy conditions before the build-up of NO at the surface site. The results revealed that during the MCMA-2006 field campaign HNO3 was primarily produced from the reaction of OH with NO2 and regulated by gas/particle transfer and dry deposition. The production of HNO3 from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

Zheng, J.; Zhang, R.; Fortner, E. C.; Volkamer, R. M.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gaeggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

2008-11-01

263

Measurements of HNO3 and N2O5 using Ion drift - Chemical Ionization Mass Spectrometry during the MCMA - 2006 Campaign  

NASA Astrophysics Data System (ADS)

An ion drift - chemical ionization mass spectrometry (ID-CIMS) was deployed in Mexico City between 5 and 31 March to measure HNO3 and N2O5 during the 2006 Mexico City Metropolitan Area (MCMA) field campaign. The observation site, T0, was located at the Instituto Mexicano del Petróleo at the center of the Mexico City Basin with major emissions of pollutants from both domestic and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and in the early morning, increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good correlation in the HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with aerosol nitrate, suggesting that the gaseous HNO3 concentration was controlled by the gas-particle partitioning process. During most times of the MCMA 2006 field campaign, N2O5 was found to be under the detection limit (about 20 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio (>100 ppb) during the night. With one exception on 26 March 2006, about 40 ppt N2O5 was observed during the late afternoon and early evening hours under a cloudy condition, before NO built up at the surface site. The results revealed that during the 2006 MCMA field campaign HNO3 was primarily produced by the reaction of OH with NO2 and regulated by gas/particle partitioning, and HNO3 production from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

Zheng, J.; Zhang, R.; Fortner, E. C.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gäggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

2008-03-01

264

Negative Numbers  

NSDL National Science Digital Library

This article is an account of how negative numbers became part of the "vocabulary" of mathematicians and of some of the earliest appearances of negative numbers in calculations of the ancient civilizations of China, India and Greece. Although negative numbers were used in calculations, negative answers to mathematical problems were considered meaningless or impossible. The troubled history of negative numbers presented in this article shows how the simple mathematical principles taken for granted today have taken thousands of years to develop.

Howard, Jill

2009-05-01

265

Negative ion formation in electrospray mass spectrometry.  

PubMed

Analytical and Chemical Sciences, Research Triangle Institute, Research Triangle Park, North Carolina, USA Negative ion electrospray (ES) operating on a single quadrupole mass spectrometer for the detection of low-molecular-weight molecules is discussed. The ES interface was operated at a positive cylindrical electrode potential to produce negative ions, and the results obtained were compared to the positive ion mode. As in the case of operation in the more common positive mode, negative ions with varying degrees of solvation and structurally relevant fragments can be obtained from a variety of solute species, including ?-lactam antibiotics, aminoglycosides, aminocyclitols, tetracyclines, sulfonamides, nucleotides, peptides, and explosives. No fragmentation of parent species, except those from some labile explosives, was provided because low potential differences are applied between the capillary and the first skimmer, and electrical discharge is avoided in the gas phase. An increase in the capillary voltage resulted in collision-induced decomposition to produce structurally relevant fragment ions in both operation modes. An evaluation of representative chromatographic solvents indicated that 2-propanol added with oxygen in the ES bath gas is best suited to suppress electrical (corona) discharge phenomena in negative ion operation, whereas it aids in solution nebulization, desolvation, and transfer of ions in solution to the gas phase. For positive ion mode, no such precaution was necessary. Conditions that promote the formation of ions in solution usually improve ES response. Therefore, an increase in the solvent pH can increase the sensitivity in negative ion ES ionization. Negative ion ES offers the advantage of providing complementary structural information to help in the characterization of an unknown compound or to confirm a certain tentatively proposed structure. Nucleotides and explosives were best characterized in negative ion mode owing to the ease with which they form anions in solution, and they could be detected down to the l-pg /gML level. PMID:24227644

Straub, R F; Voyksner, R D

1993-07-01

266

Dual-sensitive probe 1-imidazole-2-(5benzoacridine)-ethanone for the determination of amines in environmental water using HPLC with fluorescence detection and online atmospheric chemical ionization-mass spectrometry identification  

Microsoft Academic Search

Dual-sensitive probe of 1-imidazole-2-(5-benzoacridine)-ethanone (IBAE) for the determination of free amines with fluorescence detection and online highly sensitive atmospheric chemical ionization-mass spectrometry identification (APCI-MS) has been developed. 2-(Benzoacridine)-5-acetic acid (BAAA) reacts with coupling agent N,N?-carbonyldiimidazole (CDI) to form a highly activated amide intermediate 1-imidazole-2-(5-benzoacridine)-ethanone (IBAE), which is dual-sensitive probe. The amide intermediate (IBAE) reacts preferably with amines in dimethylformamide (DMF)

Jinmao You; Cuihua Song; Yanyan Fu; Zhiwei Sun; Lian Xia; Yulin Li; Yourui Suo

2010-01-01

267

Determination of a novel substance P inhibitor in human plasma by high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometric detection using single and triple quadrupole detectors  

Microsoft Academic Search

Methods based on high-performance liquid chromatography (HPLC) with atmospheric-pressure chemical ionization (APCI) mass spectrometric (MS) detection using either single (MS) or triple (MS\\/MS) quadrupole mass spectrometric detection for the determination of (2R)-[1(R)-(3,5-bis-trifluoromethylphenyl)ethoxy]-3(S)-(4-fluoro-phenyl)morpholin-4-ylmethyl]-5-oxo-4,5-dihydro-[1,2,4]triazol)methyl morpholine (Aprepitant, Fig. 1) in human plasma has been developed. Aprepitant (I) and internal standard (II, Fig. 1) were isolated from the plasma matrix buffered to pH 9.8

M. L Constanzer; C. M Chavez-Eng; J Dru; W. F Kline; B. K Matuszewski

2004-01-01

268

Three chamber negative ion source  

DOEpatents

It is an object of this invention provide a negative ion source which efficiently provides a large flux of negatively ionized particles. This invention provides a volume source of negative ions which has a current density sufficient for magnetic fusion applications and has electrons suppressed from the output. It is still another object of this invention to provide a volume source of negative ions which can be electrostatically accelerated to high energies and subsequently neutralized to form a high energy neutral beam for use with a magnetically confined plasma.

Leung, K.N.; Ehlers, K.W.; Hiskes, J.R.

1983-11-10

269

Single photon K(-2) and K(-1)K(-1) double core ionization in C(2)H(2n) (n=1-3), CO, and N(2) as a potential new tool for chemical analysis.  

PubMed

We have observed single photon double K-shell photoionization in the C(2)H(2n) (n=1-3) hydrocarbon sequence and in N(2) and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K(-2) process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K(-1)K(-1) process). In the C(2)H(2n) sequence, the spectroscopy of K(-1)K(-1) states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K(-1)K(-1) double core ionization in the C(2)H(2n) sequence and in the isoelectronic C(2)H(2n), N(2) and CO molecules validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case. PMID:23679597

Nakano, M; Penent, F; Tashiro, M; Grozdanov, T P; Žitnik, M; Carniato, S; Selles, P; Andric, L; Lablanquie, P; Palaudoux, J; Shigemasa, E; Iwayama, H; Hikosaka, Y; Soejima, K; Suzuki, I H; Kouchi, N; Ito, K

2013-04-19

270

Single Photon K-2 and K-1K-1 Double Core Ionization in C2H2n (n=1-3), CO, and N2 as a Potential New Tool for Chemical Analysis  

NASA Astrophysics Data System (ADS)

We have observed single photon double K-shell photoionization in the C2H2n (n=1-3) hydrocarbon sequence and in N2 and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K-2 process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K-1K-1 process). In the C2H2n sequence, the spectroscopy of K-1K-1 states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K-1K-1 double core ionization in the C2H2n sequence and in the isoelectronic C2H2, N2 and CO molecules validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

Nakano, M.; Penent, F.; Tashiro, M.; Grozdanov, T. P.; Žitnik, M.; Carniato, S.; Selles, P.; Andric, L.; Lablanquie, P.; Palaudoux, J.; Shigemasa, E.; Iwayama, H.; Hikosaka, Y.; Soejima, K.; Suzuki, I. H.; Kouchi, N.; Ito, K.

2013-04-01

271

Novel two-step laser ablation and ionization mass spectrometry (2S-LAIMS) of actor-spectator ice layers: Probing chemical composition of D{sub 2}O ice beneath a H{sub 2}O ice layer  

SciTech Connect

In this work, we report for the first time successful analysis of organic aromatic analytes imbedded in D{sub 2}O ices by novel infrared (IR) laser ablation of a layered non-absorbing D{sub 2}O ice (spectator) containing the analytes and an ablation-active IR-absorbing H{sub 2}O ice layer (actor) without the analyte. With these studies we have opened up a new method for the in situ analysis of solids containing analytes when covered with an IR laser-absorbing layer that can be resonantly ablated. This soft ejection method takes advantage of the tenability of two-step infrared laser ablation and ultraviolet laser ionization mass spectrometry, previously demonstrated in this lab to study chemical reactions of polycyclic aromatic hydrocarbons (PAHs) in cryogenic ices. The IR laser pulse tuned to resonantly excite only the upper H{sub 2}O ice layer (actor) generates a shockwave upon impact. This shockwave penetrates the lower analyte-containing D{sub 2}O ice layer (spectator, a non-absorbing ice that cannot be ablated directly with the wavelength of the IR laser employed) and is reflected back, ejecting the contents of the D{sub 2}O layer into the vacuum where they are intersected by a UV laser for ionization and detection by a time-of-flight mass spectrometer. Thus, energy is transmitted from the laser-absorbing actor layer into the non-absorbing spectator layer resulting its ablation. We found that isotope cross-contamination between layers was negligible. We also did not see any evidence for thermal or collisional chemistry of PAH molecules with H{sub 2}O molecules in the shockwave. We call this “shockwave mediated surface resonance enhanced subsurface ablation” technique as “two-step laser ablation and ionization mass spectrometry of actor-spectator ice layers.” This method has its roots in the well-established MALDI (matrix assisted laser desorption and ionization) method. Our method offers more flexibility to optimize both the processes—ablation and ionization. This new technique can thus be potentially employed to undertake in situ analysis of materials imbedded in diverse media, such as cryogenic ices, biological samples, tissues, minerals, etc., by covered with an IR-absorbing laser ablation medium and study the chemical composition and reaction pathways of the analyte in its natural surroundings.

Yang, Rui, E-mail: ryang73@ustc.edu; Gudipati, Murthy S., E-mail: gudipati@jpl.nasa.gov [Science Division, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-301, 4800 Oak Grove Drive, Pasadena, California 91109 (United States)

2014-03-14

272

Liquid chromatography electrospray tandem mass spectrometric and desorption electrospray ionization tandem mass spectrometric analysis of chemical warfare agents in office media typically collected during a forensic investigation  

Microsoft Academic Search

Most prior analytical studies have dealt with the determination of chemical warfare agents in environmental or biological matrices that would typically be collected following battlefield use or in support of the Chemical Weapons Convention. These methods may be useful for some investigations, but may not be practical for indoor forensic investigations where chemical warfare agent use is suspected. There is

P. A. D’Agostino; J. R. Hancock; C. L. Chenier; C. R. Jackson Lepage

2006-01-01

273

Negative ion formation processes: A general review  

SciTech Connect

The principal negative ion formation processes will be briefly reviewed. Primary emphasis will be placed on the more efficient and universal processes of charge transfer and secondary ion formation through non-thermodynamic surface ionization. 86 refs., 20 figs.

Alton, G.D.

1990-01-01

274

Treatment of Amaranthus cruentus with chemical and biological inducers of resistance has contrasting effects on fitness and protection against compatible Gram positive and Gram negative bacterial pathogens.  

PubMed

Amaranthus cruentus (Ac) plants were treated with the synthetic systemic acquired resistance (SAR) inducer benzothiadiazole (BTH), methyl jasmonate (MeJA) and the incompatible pathogen, Pseudomonas syringae pv. syringae (Pss), under greenhouse conditions. The treatments induced a set of marker genes in the absence of pathogen infection: BTH and Pss similarly induced genes coding for pathogenesis-related and antioxidant proteins, whereas MeJA induced the arginase, LOX2 and amarandin 1 genes. BTH and Pss were effective when tested against the Gram negative pathogen Ps pv. tabaci (Pst), which was found to have a compatible interaction with grain amaranth. The resistance response appeared to be salicylic acid-independent. However, resistance against Clavibacter michiganensis subsp. michiganensis (Cmm), a Gram positive tomato pathogen also found to infect Ac, was only conferred by Pss, while BTH increased susceptibility. Conversely, MeJA was ineffective against both pathogens. Induced resistance against Pst correlated with the rapid and sustained stimulation of the above genes, including the AhPAL2 gene, which were expressed both locally and distally. The lack of protection against Cmm provided by BTH, coincided with a generalized down-regulation of defense gene expression and chitinase activity. On the other hand, Pss-treated Ac plants showed augmented expression levels of an anti-microbial peptide gene and, surprisingly, of AhACCO, an ethylene biosynthetic gene associated with susceptibility to Cmm in tomato, its main host. Pss treatment had no effect on productivity, but compromised growth, whereas MeJA reduced yield and harvest index. Conversely, BTH treatments led to smaller plants, but produced significantly increased yields. These results suggest essential differences in the mechanisms employed by biological and chemical agents to induce SAR in Ac against bacterial pathogens having different infection strategies. This may determine the outcome of a particular plant-pathogen interaction, leading to resistance or susceptibility, as in Cmm-challenged Ac plants previously induced with Pss or BTH, respectively. PMID:24913050

Casarrubias-Castillo, Kena; Martínez-Gallardo, Norma A; Délano-Frier, John P

2014-07-01

275

Cosmic ray ionization of the Jovian atmosphere  

NASA Technical Reports Server (NTRS)

An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic-ray-induced cascade may be especially important in ionizing the atmosphere at levels where the total number density exceeds 10 to the 19th per cu cm (well below the ionospheric layers produced by solar EUV). A model containing both positive and negative ion reactions has been employed to compute electron and ion number densities. Peak electron number densities of the order of 1000 per cu cm may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH4(+) and CnHm(+) cluster ions, with n at least 2; it is suggested that the absorption of galactic cosmic-ray energy at such relatively high pressures in the Jovian atmosphere (M about 10 to the 18th to 10 to the 20th per cu cm) and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.

Capone, L. A.; Dubach, J.; Whitten, R. C.; Prasad, S. S.

1979-01-01

276

Chemical protection against the long-term effects of a single whole-body exposure of mice to ionizing radiation. I. Life shortening. [X radiation  

Microsoft Academic Search

A systematic study has been made of the advantages gained by treatment with combined radiochemical protectors for long-term survival of mice exposed to a single dose of ionizing radiation. Our results demonstrate that mixtures of radioprotectors increase the degree of protection compared with that obtained with each substance given separately. The dose-effect curves for the long-term survival obtained for irradiated

J. R. Maisin; G. Mattelin; M. Lambiet-Collier

1977-01-01

277

Ionizable-Substance Detector  

NASA Technical Reports Server (NTRS)

Device that includes all conventional components of fuel cell and electrolyzer continuously monitors concentration of ionizable substance in stream of fluid without significantly disrupting flow or chemical composition. Among substances monitored are hydrogen, sodium, fluorine, chlorine, oxygen, and bromine. Useful in early detection of fluctuations, malfunctions, or hazards. Particularly useful for detecting hydrogen in stream of water in closed system containing oxygen, wherein concentration of hydrogen must not exceed given maximum, lest hydrogen react explosively with oxygen. Also used to monitor exhaust stream to comply with environmental-protection requirements.

Mcelroy, William; Smith, William

1991-01-01

278

Identification of oxidized organic atmospheric species during the Southern Oxidant and Aerosol Study (SOAS) using a novel Ion Mobility Time-of-Flight Chemical Ionization Mass Spectrometer (IMS-ToF-CIMS)  

NASA Astrophysics Data System (ADS)

We present results from the field deployment of a novel Ion Mobility Time-of-flight Chemical Ionization Mass Spectrometer (CI-IMS-TOF) during the Southern Oxidant and Aerosol Study (SOAS). IMS-TOF is a 2-dimensional analysis method, which separates gas-phase ions by mobility prior to determination of mass-to-charge ratio by mass spectrometry. Ion mobility is a unique physical property that is determined by the collisional cross section of an ion. Because mobility depends on size and shape, the IMS measurement is able to resolve isomers and isobaric compounds. Additionally, trends in IMS-TOF data space can be used to identify relationships between ions, such as common functionality or polymeric series. During SOAS we interfaced the IMS-TOF to a nitrate ion (NO3-) chemical ionization source that enables the selective ionization of highly oxidized gas phase species (those having a high O:C ratio) through clustering with the reagent ion. Highly oxidized products of terpenes and isoprene are important secondary organic aerosol precursors (SOA) that play an uncertain but important role in particle-phase chemistry. We present several case studies of atmospheric events during SOAS that exhibited elevated concentrations of sulfuric acid and/or organics. These events exhibited a rise in particle number and provide an opportunity to examine the role that organic species may have in local atmospheric new particle formation events. We also present the results from the field deployment and subsequent laboratory studies utilizing a Potential Aerosol Mass (PAM) flow reactor as the inlet for the CI-IMS-TOF. The reactor draws in ambient air and exposes it to high concentrations of the OH radical, created by photolysis O3 in the presence of water. The highly oxidized products are then sampled directly by the CI-IMS-TOF. We performed several experiments including placing pine and deciduous plants directly in front of the reactor opening and observed large increases in the number and concentration of oxidized gas-phase species. Finally, we present preliminary results of atmospheric filter analysis using an Electrospray Ionization (ESI) source interfaced to the IMS-TOF.

Krechmer, J.; Canagaratna, M.; Kimmel, J.; Junninen, H.; Knochenmuss, R.; Cubison, M.; Massoli, P.; Stark, H.; Jayne, J. T.; Surratt, J. D.; Jimenez, J. L.; Worsnop, D. R.

2013-12-01

279

Elucidation of structural restraints for phosphate residues with different hydrogen bonding and ionization states.  

PubMed

Solid state NMR spectroscopy and gauge including atomic orbital (GIAO) theoretical calculations were employed to establish structural restraints (ionization, hydrogen bonding, spatial arrangement) for O-phosphorylated l-threonine derivatives in different ionization states and hydrogen bonding strengths. These structural restraints are invaluable in molecular modeling and docking procedures for biological species containing phosphoryl groups. Both the experimental and the GIAO approach show that 31P delta ii chemical shift tensor parameters are very sensitive to the ionization state. The negative values found for the skew kappa are typical for -2 phosphates. The distinct span Omega values reflect the change of strength of hydrogen bonding. For species in the -1 ionization state, engaged in very strong hydrogen bonds, Omega is smaller than for a phosphate group involved in weak hydrogen bonding. For phosphates in the -2 ionization state, Omega is significantly smaller compared to -1 species, although the kappa for -1 samples never reaches negative values. For -1 phosphate residues, in the case when 1H one pulse and/or combined rotation and multiple pulse spectroscopy (CRAMPS) sequences fail and assignment of proton chemical shift is ambiguous, a combination of 1H-(13)C and 1H-(31)P 2D heteronuclear correlation (HETCOR) correlations is found to be an excellent tool for the elucidation of 1H isotropic chemical shifts. In addition, a 2D strategy using 1H-(1)H double quantum filter (DQF) correlations [a back-to-back (BABA) sequence in this work] is useful for analyzing the topology of hydrogen bonding. In the case of a multicenter phosphorus domain, 2D 31P-(31)P proton driven spin diffusion experiments give information about the spatial arrangement of the phosphate residues. PMID:18842016

Gajda, J; Olejniczak, S; Bryndal, I; Potrzebowski, M J

2008-11-01

280

Negative muon chemistry: the quantum muon effect and the finite nuclear mass effect.  

PubMed

The any-particle molecular orbital method at the full configuration interaction level has been employed to study atoms in which one electron has been replaced by a negative muon. In this approach electrons and muons are described as quantum waves. A scheme has been proposed to discriminate nuclear mass and quantum muon effects on chemical properties of muonic and regular atoms. This study reveals that the differences in the ionization potentials of isoelectronic muonic atoms and regular atoms are of the order of millielectronvolts. For the valence ionizations of muonic helium and muonic lithium the nuclear mass effects are more important. On the other hand, for 1s ionizations of muonic atoms heavier than beryllium, the quantum muon effects are more important. In addition, this study presents an assessment of the nuclear mass and quantum muon effects on the barrier of He? + H2 reaction. PMID:25188920

Posada, Edwin; Moncada, Félix; Reyes, Andrés

2014-10-01

281

Real-time air monitoring of mustard gas and lewisite 1 by detecting their in-line reaction products by atmospheric pressure chemical ionization ion trap tandem mass spectrometry with counterflow ion introduction.  

PubMed

A new method enabling sensitive real-time air monitoring of highly reactive chemical warfare agents, namely, mustard gas (HD) and Lewisite 1 (L1), by detecting ions of their in-line reaction products instead of intact agents, is proposed. The method is based on corona discharge-initiated atmospheric pressure chemical ionization coupled with ion trap tandem mass spectrometry (MS(n)) via counterflow ion introduction. Therefore, it allows for highly sensitive and specific real-time detection of a broad range of airborne compounds. In-line chemical reactions, ionization reactions, and ion fragmentations of these agents were investigated. Mustard gas is oxygenated in small quantity by reactive oxygen species generated in the corona discharge. With increasing air humidity, the MS(2) signal intensity of protonated molecules of mono-oxygenated HD decreases but exceeds that of dominantly existing intact HD. This result can be explained in view of proton affinity. Lewisite 1 is hydrolyzed and oxidized. As the humidity increases from zero, the signal of the final product, namely, didechlorinated, dihydroxylated, and mono-oxygenated L1, quickly increases and reaches a plateau, giving the highest MS(2) and MS(3) signals among those of L1 and its reaction products. The addition of minimal moisture gives the highest signal intensity, even under low humidity. The method was demonstrated to provide sufficient analytical performance to meet the requirements concerning hygienic management and counter-terrorism. It will be the first practical method, in view of sensitivity and specificity, for real-time air monitoring of HD and L1 without sample pretreatment. PMID:25553788

Okumura, Akihiko; Takada, Yasuaki; Watanabe, Susumu; Hashimoto, Hiroaki; Ezawa, Naoya; Seto, Yasuo; Sekiguchi, Hiroshi; Maruko, Hisashi; Takayama, Yasuo; Sekioka, Ryoji; Yamaguchi, Shintaro; Kishi, Shintaro; Satoh, Takafumi; Kondo, Tomohide; Nagashima, Hisayuki; Nagoya, Tomoki

2015-01-20

282

Development of a quantification method for digoxin, a typical P-glycoprotein probe in clinical and non-clinical studies, using high performance liquid chromatography-tandem mass spectrometry: the usefulness of negative ionization mode to avoid competitive adduct-ion formation.  

PubMed

Highly sensitive and accurate liquid chromatography-tandem mass spectrometry (LC/MS/MS) methods have been developed and validated for measuring digoxin (DGX), a typical P-glycoprotein probe, in human plasma, rat plasma, and rat brain. We extracted DGX and deuterium-labeled DGX (as internal standard) from sample fluids under basic conditions using acetonitrile and sodium chloride-saturated 0.1 mol/L sodium hydroxide. The upper organic layer was diluted with distilled water, and the resulting solution was injected into an LC/MS/MS system in negative ionization mode. Chromatographic separation was achieved on a C(18)-ODS column in the gradient mobile phase, which comprised 0.05% (w/v) ammonium carbonate (pH 9.0) and methanol at a flow rate of 0.7 mL/min. Regardless of the type of biological matrix, intra-day and inter-day validation tests demonstrated good linearity of calibration curves within ranges of 0.1-10 ng/mL for plasma and 0.5-50 ng/g for rat brain and gave excellent accuracy and precision of quality control samples at 4 concentration levels. Unlike existing methods, our approach uses negative ionization to avoid competitive adduct formation of DGX. Our method showed higher sensitivity and wider applicability to various types of biological matrices than existing methods. Our method will support clinical and preclinical investigation of in vivo P-glycoprotein functionality using DGX. PMID:22098716

Hirabayashi, Hideki; Sugimoto, Hiroshi; Matsumoto, Shinichi; Amano, Nobuyuki; Moriwaki, Toshiya

2011-12-15

283

Development of Soft Ionization for Particulate Organic Detection with the Aerodyne Aerosol Mass Spectrometer  

SciTech Connect

During this DOE SBIR Phase II project, we have successfully developed several soft ionization techniques, i.e., ionization schemes which involve less fragmentation of the ions, for use with the Aerodyne time-of-flight aerosol mass spectrometer (ToF-AMS). Vacuum ultraviolet single photon ionization was demonstrated in the laboratory and deployed in field campaigns. Vacuum ultraviolet single photon ionization allows better identification of organic species in aerosol particles as shown in laboratory experiments on single component particles, and in field measurements on complex multi-component particles. Dissociative electron attachment with lower energy electrons (less than 30 eV) was demonstrated in the measurement of particulate organics in chamber experiments in Switzerland, and is now a routine approach with AMS systems configured for bipolar, negative ion detection. This technique is particularly powerful for detection of acidic and other highly oxygenated secondary organic aerosol (SOA) chemical functionality. Low energy electron ionization (10 to 12 eV) is also a softer ionization approach routinely available to AMS users. Finally, Lithium ion attachment has been shown to be sensitive to more alkyl-like chemical functionality in SOA. Results from Mexico City are particularly exciting in observing changes in SOA molecular composition under different photochemical/meteorological conditions. More recent results detecting biomass burns at the Montana fire lab have demonstrated quantitative and selective detection of levoglucosan. These soft ionization techniques provide the ToF-AMS with better capability for identifying organic species in ambient atmospheric aerosol particles. This, in turn, will allow more detailed study of the sources, transformations and fate of organic-containing aerosol.

Trimborn, A; Williams, L R; Jayne, J T; Worsnop, D R

2008-06-19

284

Gas-phase positive and negative ion/molecule reactions in diborane and silane/diborane mixtures  

NASA Astrophysics Data System (ADS)

The gas phase ion chemistry of diborane and of silane/diborane mixtures was studied by ion trap mass spectrometry (ITMS), in both positive and negative ionization mode. Positive ion/molecule reactions in diborane mainly proceed through H2 or BH3 loss and lead to formation of B hydride clusters containing up to six B atoms, while in negative ionization clustering reactions proceed to a higher degree with formation of B8Hn- ions. In the silane/diborane system, the main ion/molecule reactions leading to ions containing both silicon and boron atoms were identified and rate constants of the main processes were determined for positive ions. In positive ionization, Si/B ions are mainly formed in reactions of few diborane ions with silane, while reactions of silane ions with B2H6 yield B2H5+ as the main product. Negative ionization of the same mixture produces a much larger amount of Si/B ionic species, due to several reactions of silane anions with diborane, resulting in BH3 or H2 neutral losses. These results indicate that negative ions may play an important role in formation of Si/B ion clusters in plasma chemical vapour deposition processes for production of semiconductor and photovoltaic materials.

Operti, Lorenza; Rabezzana, Roberto; Turco, Francesca; Vaglio, Gian Angelo

2007-06-01

285

The PI4+ cation has an extremely large negative 31P nuclear magnetic resonance chemical shift, due to spin-orbit coupling: A quantum-chemical prediction and its confirmation by solid-state nuclear magnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

We have used density-functional methods including explicit spin-orbit corrections, to calculate the 31P nuclear magnetic resonance (NMR) chemical shifts of the tetrahalophosphonium cations PX4+ (X=F, Cl, Br, I). The agreement between theory and experimental literature data for PF4+, PCl4+, and PBr4+ is good. For PI4+, the calculations predict an extremely negative (high-field) shift of approximately -520 ppm, due to particularly large spin-orbit contributions from the four heavy iodine substituents, transmitted to the phosphorus nucleus by a very effective Fermi-contact mechanism. No experimental data were available for PI4+. We have, therefore, prepared the compounds PI4AsF6, PI4SbF6, PI4AlI4, and PI4GaI4 and recorded their solid-state 31P NMR spectra, both with and without magic-angle spinning of the sample. Using the noncoordinating AsF6- and SbF6- anions, the measured isotropic shifts are -519 and -517 ppm, respectively, in good agreement with the predicted extreme value for the isolated cation. In contrast, ?31P values of only -304 and -295 ppm are found for PI4AlI4 and PI4GaI4, respectively. The large deviation from the isolated-cation limit in the latter two compounds is probably related to significant I⋯I secondary bonding interactions, as found in the solid-state structure of PI4AlI4. The observed solid-state shift tensors are discussed. The present results disagree clearly with previous claims for the synthesis of PI5.

Kaupp, Martin; Aubauer, Christoph; Engelhardt, Günter; Klapötke, Thomas M.; Malkina, Olga L.

1999-02-01

286

[Regional medico-dosimetric register (RMDR) is a model for evaluation of long-term "low" dose ionizing radiation effects on Siberian group of chemical enterprises main production personnel].  

PubMed

Medico-dosimetric register is an optimal model of epidemiological studies on evaluation of ionizing radiation effects. Regional medico-dosimetric register (RMDR) is a system of interrelating information blocks including data on Siberian Group of Chemical Enterprises (SGCE) personnel. At present SGCE personnel and Seversk residents RMDR database includes information on 138496 persons, 65538 of which are SGCE workers. SGCE personnel and Seversk residents RMDR is a scientific base for researches with the aim of evaluating long-term ionizing radiation effects in a "low" dose range. Information on mortality and morbidity rate as well as "thematic" registers of the main diseases potentiates in evaluating the spectrum of somatic stochastic effects and radiogenic risks in SGCE workers and Seversk residents as well as their offsprings. A practical significance of RMDR database is the formation of the main diseases "risk" groups depending on definite risk factors in certain groups that provides targeted diagnostic and preventive therapy both among high-dose establishments' workers and residents living near-by. PMID:18689256

Takhauov, R M; Karpov, A B; Vysotski?, O A; Vostrova, Zh O; Dolgopolov, Iu V; Andreev, G S; Dubin, V V; Fre?din, M B; Vasil'eva, E O; Semenova, Iu V; Voronova, I A; Litvinenko, T M; Dvornichenko, M V; Grishaev, L V; Beliaeva, T S

2008-01-01

287

Investigation of the interaction between enzyme and inhibitor by the combination of chemical modification, electrospray ionization mass spectrometry and frit-fast atom bombardment liquid chromatography/mass spectrometry.  

PubMed

The interaction between enzyme and its inhibitor, hen egg-white lysozyme and tri-N-acetylglucosamine (NAG3), was studied by the combination of chemical modification, enzymatic digestion, electrospray ionization mass spectrometry and frit-fast atom bombardment liquid chromatography/mass spectrometry. Chemical modification of amino groups, carboxyl groups, and indole groups was carried out independently. In the absence of NAG3, the carboxyl group in Asp 101 was modified by glycinamidation, and the indole group in Trp 62 was modified by Koshland reagent. In the presence of NAG3, the degree of modification of Asp 101 and Trp 62 decreased. It is suggested that Asp 101 and Trp 62 are involved in the interaction with NAG3. The result is consistent with the one obtained by x-ray crystallography. It is indicated that the combination of chemical modification and mass spectrometry may be effective for the investigation of the binding reaction of enzyme to inhibitor and of protein-protein interaction. PMID:8448221

Akashi, S; Niitsu, U; Yuji, R; Ide, H; Hirayama, K

1993-02-01

288

Negative ion spectrometry for detecting nitrated explosives  

NASA Technical Reports Server (NTRS)

Ionization procedure is modified to produce mainly negative ions by electron capture. Peaks of negative ions are monitored conventionally. Nitrated organic materials could be identified directly from sample sniff inlet stream by suitably modified mass spectrometer because of unique electronegativity which nitro group imparts to organic material.

Boettger, H. G.; Yinon, J.

1975-01-01

289

Development and validation of a sensitive gas chromatography-ammonia chemical ionization mass spectrometry method for the determination of tabun enantiomers in hemolysed blood and plasma of different species.  

PubMed

The aim of this study was to develop and validate a fast, sensitive and easily applicable GC-MS assay for the chiral quantification of the highly toxic organophosphorus compound tabun (O-ethyl-N,N-dimethylphosphoramidocyanidate, GA) in hemolysed swine blood for further use in toxicokinetic and toxicodynamic studies. These requirements were fulfilled best by a GC-MS assay with positive chemical ionization with ammonia (GC-PCI-MS). Separation was carried out on a beta-cyclodextrin capillary column (Supelco BetaDex 225) after reversed phase (C18) solid-phase extraction. The limit of detection was 1 pg/ml for each enantiomer (approximately 500 fg on column) and the limit of quantification 5 pg/ml. The GC-PCI-MS method was applied for the quantification of tabun enantiomers in spiked swine blood after hemolysis and in spiked plasma of different species including humans. PMID:19766064

Tenberken, Oliver; Worek, Franz; Thiermann, Horst; Reiter, Georg

2010-05-15

290

The method for on-site determination of trace concentrations of methyl mercaptan and dimethyl sulfide in air using a mobile mass spectrometer with atmospheric pressure chemical ionization, combined with a fast enrichment/separation system.  

PubMed

A method for fast simultaneous on-site determination of methyl mercaptan and dimethyl sulfide in air was developed. The target compounds were actively collected on silica gel, followed by direct flash thermal desorption, fast separation on a short chromatographic column and detection by means of mass spectrometer with atmospheric pressure chemical ionization. During the sampling of ambient air, water vapor was removed with a Nafion selective membrane. A compact mass spectrometer prototype, which was designed earlier at Trofimuk Institute of Petroleum Geology and Geophysics, was used. The minimization of gas load of the atmospheric pressure ion source allowed reducing the power requirements and size of the vacuum system and increasing its ruggedness. The measurement cycle is about 3 min. Detection limits in a 0.6 L sample are 1 ppb for methyl mercaptan and 0.2 ppb for dimethyl sulfide. PMID:24725876

Kudryavtsev, Andrey S; Makas, Alexey L; Troshkov, Mikhail L; Grachev, Mikhail ?; Pod'yachev, Sergey P

2014-06-01

291

Simultaneous extraction of acetylsalicylic acid and salicylic acid from human plasma and simultaneous estimation by liquid chromatography and atmospheric pressure chemical ionization/tandem mass spectrometry detection. Application to a pharmacokinetic study.  

PubMed

A simple analytical method using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in atmospheric chemical ionization mode (APCI) for the simultaneous estimation of acetylsalicylic acid (ASA, CAS 50-78-2) and its active metabolite salicylic acid (SA, CAS 69-72-7) in human plasma has been developed and validated. ASA and SA were analyzed simultaneously despite differences in plasma concentration ranges of ASA and SA after oral administration of ASA. In spite of having different chemical, ionization and chromatographic properties, ASA and SA were extracted simultaneously from the plasma sample using acetonitrile protein precipitation followed by liquid-liquid extraction. The analytes were separated on a reversed phase column with rapid gradient program using mobile phase consisting of ammonium acetate buffer and methanol. The structural analogue diclofenac was used as an internal standard. The multiple reaction monitoring (MRM) transitions m/z 179 --> 137 for ASA, m/z 137 --> 65 for SA and m/z 294 --> 250 for IS were used. The assay exhibited a linear dynamic range of 0.02-10 microg/mL for ASA and 0.1-50 microg/mL for SA. The between-batch precision (%CV) ranged from 2.1 to 7.9% for ASA and from 0.2 to 5.2% for SA. The between-batch accuracy ranged from 95.4 to 96.7% for ASA and from 94.6 to 111.3% for SA. The validated method was successfully applied for the evaluation of pharmacokinetics of ASA after single oral administration of 650 mg test formulation versus two 325 mg reference formulations of ASA in human subjects. PMID:21755814

Nirogi, Ramakrishna; Kandikere, Vishwottam; Mudigonda, Koteshwara; Ajjala, Devender; Suraneni, Ramakrishna; Thoddi, Parthasarathi

2011-01-01

292

A gas chromatographic-positive ion chemical ionization-mass spectrometric method for the determination of I-alpha-acetylmethadol (LAAM), norLAAM, and dinorLAAM in plasma, urine, and tissue.  

PubMed

l-alpha-Acetylmethadol (LAAM) is approved as a substitute for methadone for the treatment of opiate addiction. Analytical methods are needed to quantitate LAAM and its two psychoactive metabolites, norLAAM and dinorLAAM, to support pharmacokinetic and other studies. We developed a gas chromatographic-positive ion chemical ionization-mass spectrometric method for these analyses. The method uses 0.5 mL urine or 1.0 mL plasma or tissue homogenate, deuterated (d3) isotopomers as internal standards, methanolic denaturation of protein (for plasma and tissue), and extraction of the buffered sample with n-butyl chloride. For tissue homogenates, an acidic back extraction is included. norLAAM and dinorLAAM were derivatized with trifluoroacetic anhydride. Chromatographic separation of LAAM and derivatized norLAAM and dinorLAAM is achieved with a 5% phenyl methylsilicone capillary column. Positive ion chemical ionization detection using methane-ammonia as the reagent gas produces abundant protonated ions (MH+) for LAAM (m/z 354) and LAAM-d3 (m/z 357) and ammonia adduct ions (MNH4+) for the derivatized norLAAM (m/z 453), norLAAM-d3 (m/z 45 6), dinorLAAM (m/z 439), and dinorLAAM-d3 (m/z 442). The linear range of the calibration curves were matrix dependent: 5-300 ng/mL for plasma, 10-1000 ng/mL for urine, and 10-600 ng/g for tissue homogenates. The low calibrator was the validated limit of quantitation for that matrix. The method is precise and accurate with percent coefficients of variation and percent of targets within 13%. The method was applied to the analysis of human urine and plasma samples; rat plasma, liver, and brain samples; and human liver microsomes following incubation with LAAM. PMID:8926727

Moody, D E; Crouch, D J; Sakashita, C O; Alburges, M E; Minear, K; Schulthies, J E; Foltz, R L

1995-10-01

293

High-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry and gas chromatography-flame ionization detection characterization of Delta5-polyenoic fatty acids in triacylglycerols from conifer seed oils.  

PubMed

Edible conifer seeds can serve as a source of triacylglycerols (TGs) with unusual Delta5 unsaturated polymethylene interrupted fatty acids (UPIFAs), such as cis-5,9-octadecadienoic (taxoleic), cis-5,9,12-octadecatrienoic (pinolenic), cis-5,11-eicosadienoic (keteleeronic) and cis-5,11,14-eicosatrienoic acids (sciadonic). Conifer seed oils from European Larch (Larix decidua), Norway Spruce (Picea abies) and European Silver Fir (Abies alba) have been analyzed by non-aqueous reversed-phase high-performance liquid chromatography (NARP-HPLC) with atmospheric pressure chemical ionisation (APCI)-MS detection. The influence of different positions of double bonds in Delta5-UPIFAs on the retention and fragmentation behavior is described and used for the successful identification of TGs in each oil. TGs containing Delta5-UPIFAs have a higher retention in comparison with common TGs found in plant oils with single methylene interrupted Delta6(9)-FAs and also significantly changed relative abundances of fragment ions in APCI mass spectra. Results obtained from HPLC/MS analyses are supported by validated GC/FID analyses of fatty acid methyl esters after the transesterification. The total content of Delta5-UPIFAs is about 32% for European Larch, 27% for Norway Spruce and 20% for European Silver Fir. In total, 20 FAs with acyl chain lengths from 16 to 24 carbon atoms and from 0 to 3 double bonds have been identified in 64 triacylglycerols from 3 conifer seed oils. PMID:17307191

Lísa, Miroslav; Holcapek, Michal; Rezanka, Tomás; Kabátová, Nadezda

2007-03-30

294

Effect of moderate heating on the negative electron affinity and photoyield of air-exposed hydrogen-terminated chemical vapor deposited diamond  

E-print Network

-terminated chemical vapor deposited diamond G. Piantanida, A. Breskin, R. Chechik,a) and O. Katz Department-terminated chemical vapor deposited diamond films was studied in the photon spectral range of 140­210 nm 8.9­5.9 e on the diamond surface is responsible for the observed effect. A simple model is presented for quantitative

295

Microwave-induced plasma desorption/ionization source for ambient mass spectrometry.  

PubMed

A new ionization source based on microwave induced plasma was developed for ambient desorption/ionization. The microwave-induced plasma desorption/ionization source (MIPDI) was composed of a copper Surfatron microwave cavity where a fused-silica tube was centered axially. Stable nonlocal thermodynamic equilibrium plasma was generated in the quartz discharge tube when a microwave at a frequency of 2450 MHz was coupled to the microwave cavity. Analytes deposited on the surface of poly(tetrafluoroethylene) (PTFE) or quartz slide after hydrofluoric acid (HF) etching were desorbed and ionized by the plasma. The performance of the MIPDI technique was validated by the analysis of a variety of chemical substances, polymer compounds, and pharmaceutical drugs using argon or helium as the discharge gas. Protonated [M + H](+) or deprotonated [M - H](-) ions were observed in the positive or negative mode. MIPDI was also used for the analysis of compounds in a complex matrix without any sample preparation. MIPDI was also capable of analyzing liquid samples. The signal-to-noise ratio was 463 in the analysis of 9.2 ng of phenylalanine, and the limit of detection was 60 pg for phenylalanine. MIPDI could desorb and ionize analytes with a molecular weight of up to 1200, which was demonstrated by the analysis of polyethylene glycol 800 (PEG800). MIPDI has advantages of simple instrumentation, relatively high temperature, stability, and reproducibility. PMID:23534913

Zhan, Xuefang; Zhao, Zhongjun; Yuan, Xin; Wang, Qihui; Li, Dandan; Xie, Hong; Li, Xuemei; Zhou, Meigui; Duan, Yixiang

2013-05-01

296

Ionization potentials of seaborgium  

Microsoft Academic Search

Multiconfiguration relativistic Dirac-Fock values were calculated for the first six ionization potentials of seaborgium and of the other group 6 elements. No experimental ionization potentials are available for seaborgium. Accurate experimental values are not available for all of the other ionization potentials. Ionic radii for the 4+ through 6+ ions of seaborgium are also presented. The ionization potentials and ionic

E. Johnson; V. Pershina; B. Fricke

1999-01-01

297

Negative-ion source applications.  

PubMed

In this paper heavy negative-ion sources which we developed and their applications for materials science are reviewed. Heavy negative ions can be effectively produced by the ejection of a sputtered atom through the optimally cesiated surface of target with a low work function. Then, enough continuous negative-ion currents for materials-science applications can be obtained. We developed several kinds of sputter-type heavy negative-ion sources such as neutral- and ionized-alkaline metal bombardment-type heavy negative-ion source and rf-plasma sputter type. In the case where a negative ion is irradiated on a material surface, surface charging seldom takes place because incoming negative charge of the negative ion is well balanced with outgoing negative charge of the released secondary electron. In the negative-ion implantation into an insulator or insulated conductive material, high precision implantation processing with charge-up free properties can be achieved. Negative-ion implantation technique, therefore, can be applied to the following novel material processing systems: the surface modification of micrometer-sized powders, the nanoparticle formation in an insulator for the quantum devices, and the nerve cell growth manipulation by precise control of the biocompatibility of polymer surface. When a negative ion with low kinetic energy approaches the solid surface, the kinetic energy causes the interatomic bonding (kinetic bonding), and formation of a metastable material is promoted. Carbon films with high constituent of sp(3) bonding, therefore, can be formed by carbon negative-ion beam deposition. PMID:18315249

Ishikawa, J

2008-02-01

298

Concerning the ionization of large polyatomic molecules with intense ultrafast lasers  

E-print Network

ionization MPI to tunnel ionization. It is also demonstrated that this structure-based model can yields. This is essential when intense fields are used in detection schemes for chemical dynamics radiation-molecule coupling and the relative ionization prob- abilities in the limit of tunnel ionization

Levis, Robert J.

299

Studies of nanosecond pulse surface ionization wave discharges over solid and liquid dielectric surfaces  

NASA Astrophysics Data System (ADS)

Surface ionization wave discharges generated by high-voltage nanosecond pulses, propagating over a planar quartz surface and over liquid surfaces (distilled water and 1-butanol) have been studied in a rectangular cross section test cell. The discharge was initiated using a custom-made, alternating polarity, high-voltage nanosecond pulse plasma generator, operated at a pulse repetition rate of 100–500 Hz, with a pulse peak voltage and current of 10–15 kV and 7–20 A, respectively, a pulse FWHM of ?100 ns, and a coupled pulse energy of 2–9 mJ/pulse. Wave speed was measured using a capacitive probe. ICCD camera images demonstrated that the ionization wave propagated predominantly over the quartz wall or over the liquid surface adjacent to the grounded waveguide placed along the bottom wall of the test cell. Under all experimental conditions tested, the surface plasma ‘sheet’ was diffuse and fairly uniform, both for positive and negative polarities. The parameters of ionization wave discharge propagating over distilled water and 1-butanol surfaces were close to those of the discharge over a quartz wall. No perturbation of the liquid surface by the discharge was detected. In most cases, the positive polarity surface ionization wave propagated at a higher speed and over a longer distance compared to the negative polarity wave. For all three sets of experiments (surface ionization wave discharge over quartz, water and 1-butanol), wave speed and travel distance decreased with pressure. Diffuse, highly reproducible surface ionization wave discharge was also observed over the liquid butanol–saturated butanol vapor interface, as well as over the distilled water–saturated water vapor interface, without buffer gas flow. No significant difference was detected between surface ionization discharges sustained using single-polarity (positive or negative), or alternating polarity high-voltage pulses. Plasma emission images yielded preliminary evidence of charge removal from the liquid surface between the pulses on a microsecond time scale. Products of the plasma chemical reaction that accumulated in the ionization wave discharge over the liquid butanol–saturated butanol vapor interface were detected ex situ, using FTIR absorption spectroscopy. Reaction products identified include CO, alkanes (CH4,C2H6, C3H8), alkynes (C2H2), aldehydes (CH2O) and lighter alcohols (CH3OH).

Petrishchev, Vitaly; Leonov, Sergey; Adamovich, Igor V.

2014-12-01

300

The decarbonylation of ionized formamide, H---C(=O)---NH2+, and aminohydroxycarbene, HO---C---NH2+: decay via an excited state. A quantum chemical investigation  

NASA Astrophysics Data System (ADS)

The unimolecular chemistry of the title [H3,C,N,O]+ ions has been investigated by ab initio molecular orbital calculations executed at the MR-SDCI//CASSCF/DZPP+f level of theory. Metastable formamide radical cations, H2NCH0+, abundantly lose the carbon-bonded hydrogen to produce H2N---C=O+. At slightly higher energies decarbonylation to NH3+ takes effect and our calculations indicate that this reaction does not proceed via a classical 1,2-hydrogen shift but rather via ion-dipole complexes. The ground state of H2NCHO+ is the 2A' state which can be represented as the structure +NH2=C(H)---O'; to lose CO via a classical 1,2-hydrogen shift the NH2 group has to be rotated about the double bond and this requires considerable energy. However in the 2A'' state, which lies only 5 kcal mol-1 above the 2A' state, the CN [pi] molecular orbital is singly occupied and now the NH2 group may freely rotate. Decarbonylation proceeds as follows: after surface crossing 2A' --> 2A'' the single C---N bond stretches, but this does not immediately lead to dissociation to H2N'+HCO+; rather at 2.6Å a fast and irreversible proton transfer takes place in the transient H2N...HCO+ complex, leading to NH3++ CO. An appearance energy of 11.28 eV for the decarbonylation of (ionized) formamide is predicted. Aminohydroxycarbene, HO---C---NH2+, rearranges to 2A' H2NCHO+ prior to the loss of CO and H+. Our calculations are in good agreement with experiment and in addition they provide a rationalization for a large isotope effect associated with the decay of D---C(=O)---NH2+.

Ruttink, Paul J. A.; Burgers, Peter C.; Terlouw, Johan K.

1995-07-01

301

Negative probability  

E-print Network

This article was written for the Logic in Computer Science column in the February 2015 issue of the Bulletin of the European Association for Theoretical Computer Science. The intended audience is general computer science audience. The uncertainty principle asserts a limit to the precision with which position x and momentum p of a particle can be known simultaneously. You may know the probability distributions of x and p individually but the joint distribution makes no physical sense. Yet Wigner exhibited such a joint distribution f(x,p). There was, however, a little trouble with it: some of its values were negative. Nevertheless Wigner's discovery attracted attention and found applications. There are other joint distribution, all with negative values, which produce the correct marginal distributions of x and p. But only Wigner's distribution produces the correct marginal distributions for all linear combinations of position and momentum. We offer a simple proof of the uniqueness and discuss related issues.

Andreas Blass; Yuri Gurevich

2015-02-02

302

Negative-ion formation in the explosives RDX, PETN, and TNT by using the reversal electron attachment detection technique  

NASA Technical Reports Server (NTRS)

First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the 'signature' of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.

Boumsellek, S.; Alajajian, S. H.; Chutjian, A.

1992-01-01

303

Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons  

NASA Astrophysics Data System (ADS)

Ab initio calculations combining density-functional theory and nonequilibrium Green's function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the high bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect.

Yang, Xi-Feng; Zhou, Wen-Qian; Hong, Xue-Kun; Liu, Yu-Shen; Wang, Xue-Feng; Feng, Jin-Fu

2015-01-01

304

Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons.  

PubMed

Ab initio calculations combining density-functional theory and nonequilibrium Green's function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the high bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect. PMID:25591376

Yang, Xi-Feng; Zhou, Wen-Qian; Hong, Xue-Kun; Liu, Yu-Shen; Wang, Xue-Feng; Feng, Jin-Fu

2015-01-14

305

Ionization potentials of seaborgium  

SciTech Connect

Multiconfiguration relativistic Dirac-Fock values were calculated for the first six ionization potentials of seaborgium and of the other group 6 elements. No experimental ionization potentials are available for seaborgium. Accurate experimental values are not available for all of the other ionization potentials. Ionic radii for the 4+ through 6+ ions of seaborgium are also presented. The ionization potentials and ionic radii obtained will be used to predict some physiochemical properties of seaborgium and its compounds.

Johnson, E.; Pershina, V.; Fricke, B.

1999-10-21

306

ESTIMATION OF IONIZATION CONSTANTS OF AZO DYES AND RELATED AROMATIC AMINES: ENVIRONMENTAL IMPLICATIONS  

EPA Science Inventory

Ionization constants for 214 dye molecules were calculated from molecular structures using the chemical reactivity models developed in SPARC (SPARC Performs Automated Reasoning in Chemistry). hese models used fundamental chemical structure theory to predict chemical reactivities ...

307

An atmospheric pressure chemical ionization-ion-trap mass spectrometer for the on-line analysis of volatile compounds in foods: a tool for linking aroma release to aroma perception.  

PubMed

An atmospheric pressure chemical ionization ion-trap mass spectrometer was set up for the on-line analysis of aroma compounds. This instrument, which has been successfully employed for some years in several in vitro and in vivo flavour release studies, is described for the first time in detail. The ion source was fashioned from polyether ether ketone and operated at ambient pressure and temperature making use of a discharge corona pin facing coaxially the capillary ion entrance of the ion-trap mass spectrometer. Linear dynamic ranges (LDR), limits of detection (LOD) and other analytical characteristics have been re-evaluated. LDRs and LODs have been found fully compatible with the concentrations of aroma compounds commonly found in foods. Thus, detection limits have been found in the low ppt range for common flavouring aroma compounds (for example 5.3?ppt (0.82?ppbV) for ethyl hexanoate and 4.8?ppt (1.0?ppbV) for 2,5-dimethylpyrazine). This makes the instrument applicable for in vitro and in vivo aroma release investigations. The use of dynamic sensory techniques such as the temporal dominance of sensations (TDS) method conducted simultaneously with in vivo aroma release measurements allowed to get some new insights in the link between flavour release and flavour perception. PMID:25230189

Le Quéré, Jean-Luc; Gierczynski, Isabelle; Sémon, Etienne

2014-09-01

308

STRUCTURAL DETERMINATION AND QUANTITATIVE ANALYSIS OF BACTERIAL PHOSPHOLIPIDS USING LIQUID CHROMATOGRAPHY/ELECTROSPRAY IONIZATION/MASS SPECTROMETRY  

EPA Science Inventory

This report presents a comprehensive spectral analysis of common bacterial phospholipids using electrospray/mass spectrometry (ESI/MS) under both negative and positive ionization conditions. Phospholipids under positive ionization yield sodium-adduct molecular ions which are mos...

309

On the applicability of laser ionization for simulating hypervelocity impacts  

NASA Astrophysics Data System (ADS)

In-situ measurements, the direct interception and analysis of dust particles by spacecraft-based instrumentation, provide insights into the dynamical, physical and chemical properties of cosmic dust. The most sensitive detection methods for dust particles in space are based on impact ionization. Laser ionization is used for the test, development, and calibration of impact ionization instruments and to complement laboratory based particle impact experiments. A typical setup uses a 355 nm Nd-YAG laser with a pulse length of about 5 ns. It is necessary to investigate the properties of both processes with respect to their comparability. A study was performed to find out to what extent laser ionization can be used to simulate impact ionization. The findings show that laser ionization and impact ionization show similarities, which can be used to test the functionality of dust impact detectors, especially time-of-flight instruments. Our paper provides information on what extent these similarities hold and where their limits are.

Mocker, Anna; Grün, Eberhard; Sternovsky, Zoltán; Drake, Keith; Kempf, Sascha; Hornung, Klaus; Srama, Ralf

2012-11-01

310

Experimental and modeling analysis of fast ionization wave discharge propagation in a rectangular geometry  

E-print Network

Experimental and modeling analysis of fast ionization wave discharge propagation in a rectangular online 17 August 2011) Fast ionization wave (FIW), nanosecond pulse discharge propagation in nitrogen repetition rate of 20 Hz. Both negative polarity and positive polarity ionization waves have been studied

Kushner, Mark

311

Thermal ionization cavity source for mass spectrometry  

SciTech Connect

Thermal ionization mass spectrometry (TIMS) is widely used for isotopic determination, and elemental concentration measurements by isotope dilution. TIMS is applicable to over 70 elements in the periodic table, often, with very high sensitivity, low detection limits, high precision, and high accuracy. Probably due to its success and simplicity, the traditional resistively heated filament type ion source, used in TIMS, has remained relatively unchanged in the past 50 years. Only minor changes in the number of filaments used for vaporization and ionization, and the shape of the filament have been employed. Much of the science of thermal ionization has focused on sample preparation, and chemical ionization enhancers. Beyer et al., in the USSR, and Johnson et al., later in the US, introduced a new high temperature cavity-type thermal ionization source for isotope separation on-line (ISOL) projects. Delmore et al. introduced a similar cavity-type source for the study of thermal emission of primary ions for secondary ionization mass spectrometry (SIMS). A new thermal ionization cavity-type source for mass spectrometry has been developed in this laboratory.

Olivares, J.A.; Chamberlin, E.P.; Duan, Yixiang [Los Alamos National Lab., NM (United States)

1995-12-31

312

Ionization of NO at high temperature  

NASA Technical Reports Server (NTRS)

Space vehicles flying through the atmosphere at high speed are known to excite a complex set of chemical reactions in the atmospheric gases, ranging from simple vibrational excitation to dissociation, atom exchange, electronic excitation, ionization, and charge exchange. Simple arguments are developed for the temperature dependence of the reactions leading to ionization of NO, including the effect of vibrational electronic thermal nonequilibrium. NO ionization is the most important source of electrons at intermediate temperatures and at higher temperatures provides the trigger electrons that ionize atoms. Based on these arguments, recommendations are made for formulae which fit observed experimental results, and which include a dependence on both a heavy particle temperature and different vibration electron temperatures. In addition, these expressions will presumably provide the most reliable extrapolation of experimental results to much higher temperatures.

Hansen, C. Frederick

1991-01-01

313

Negative ion chemistry in Titan's upper atmosphere  

NASA Astrophysics Data System (ADS)

In the upper part of atmospheres lies the ionosphere, a region of particular interest for planetary science, because it provides the link between the neutral atmosphere, and the ionizing processes from outer space. On Titan, it is created by the interaction of solar ultraviolet radiation and magnetospheric electrons with the main atmospheric constituents, N2 and CH4. Cassini has revealed that an extremely complex chemistry occurs in Titan's ionosphere. The INMS mass spectrometer detected positively charged hydrocarbons and nitrogen-bearing species with a charge-to-mass ratio (m/z) up to 100 amu [1]. In 2007, the Electron Spectrometer (ELS), one of the sensors making up the Cassini Plasma Spectrometer (CAPS) revealed the existence of numerous negative ions in Titan's upper atmosphere [2]. The data showed evidence for negatively charged ions with m/z up to 10,000 amu and at lower m/z for two distinct peaks below 50 amu, corresponding to a total density of ~200 cm-3, giving an anion to cation ratio of ~0.1. This detection happened almost simultaneously with the surprising discovery of four negative ions in the interstellar medium: C4H-, C6H-, C8H- and C3N- [3; 4; 5; 6; 7]. The possible presence of negative ions in Titan's upper atmosphere had only been briefly discussed before the Cassini-Huygens mission. Three-body electron attachment to radicals or collisional charging of aerosols had been suggested as a source of negatively charged species. Because the first process is negligible at high altitude (neutral densities lower than 1015 cm-3) and because aerosols were not expected above ~500 km, ionospheric models considered the presence of negatively charged species to be highly unlikely. However, the observations clearly show that Titan has the most complex ionosphere of the Solar System with an intense chemistry, leading to an increase of molecular size. By analyzing the optical properties of the detached haze layer observed at 520 km in Titan's mesosphere, Lavvas et al. provided the first quantitative evidence that thermospheric chemistry is the main source of haze on Titan [8]. The negative ions observed by ELS are very likely hydrocarbon and nitrogen-bearing species but their stoichiometry and structure are largely unknown because of the poor mass resolution of the spectrometer. In order to interpret the data, it is therefore necessary to develop kinetic models of the ionosphere of Titan and confront them with repeated measurements. In order to determine the processes controlling the formation of negative ions in Titan's atmosphere we use the photochemical model developed by Vuitton et al. [9; 10]. This model was used to successfully explain the processes controlling the positive ion formation in Titan's ionosphere. Furthermore, it was used for the investigation of the ion-neutral chemical processes controlling the formation of the observed thermospheric benzene abundance [11]. In order to properly describe the negative ion chemistry, eleven negative ions and about a hundred reactions involving negatively charged species have been added to the original model. The model solves the continuity equation in onedimension at altitudes between 700 and 1500 km, assuming local chemical equilibrium. It takes into account production and loss processes that include photoionization, photodetachement, energetic electron impact, and chemical reactions between ions and neutrals and between positively and negatively charged species. Due to the small chemical lifetime of ions compared with the characteristic time for diffusion, the latter is not included in the calculations. The photoelectron flux that leads to the production of negative ions is calculated by solving the Boltzmann transfer equation that provides a stationary solution for the intensity (cm-2 s-1 eV-1 sr-1) of electrons at different energies, angles and altitudes within the atmosphere ([12] and references therein). The ion densities depend closely upon the composition of the neutral atmosphere. The density of the main atmospheric constituents, N2, CH4 and H2 are well establi

Vuitton, V.; Lavvas, P.; Yelle, R. V.; Wellbrock, A.; Lewis, G. R.; Coates, A.; Thissen, R.; Dutuit, O.

2008-09-01

314

Electrospray ionization mass spectral studies of N,N-dialkylaminoethane-2-sulphonic acids.  

PubMed

Oxidative reactions of VX type compounds and N,N-dialkylaminoethane-2-thiols that are precursors for VX compounds produce N,N-dialkylaminoethane-2-sulphonic acids, N(R(1))(R(2))-CH(2)-CH(2)SO(3)H (where R(1) and R(2) = methyl, ethyl, n-propyl and isopropyl, 1-10), as the degradation products, and these degradation products are considered as markers for the detection of chemicals listed in the schedules of Chemical Weapons Convention (CWC) chemicals. Off-site detection of such degradation products in aqueous samples is an important task in the verification of CWC-related chemicals. Here we report a simple method involving the direct analysis of aqueous samples using positive and/or negative ion electrospray ionization (ESI) for the screening, detection and identification of N,N-dialkylaminoethane-2-sulphonic acids, avoiding sample preparation and chromatographic steps. The positive ion ESI mass spectra of all the compounds result in abundant [M+Na](+) ions, and the negative ion spectra show abundant [M-H](-) ions to confirm their molecular weight. The collision-induced dissociation spectra of [M+Na](+) and [M-H](-) give characteristic product ions by which it is easy to detect and identify all the studied N,N-dialkylaminoethane-2-sulphonic acids including those of isomeric compounds. The method is successfully applied to detect the spiked chemical, N,N-diisopropylaminoethane-2-sulphonic acid, present in a water sample received in a proficiency test. PMID:17979103

Lakshmi, V V S; Prabhakar, S; Murty, M R V S; Vairamani, M

2007-01-01

315

Martian Meteor Ionization Layers  

NASA Technical Reports Server (NTRS)

Small interplanetary grains bombard Mars, like all the solar system planets, and, like all the planets with atmospheres, meteoric ion and atom layers form in the upper atmosphere. We have developed a comprehensive one-dimensional model of the Martian meteoric ionization layer including a full chemical scheme. A persistent layer of magnesium ions should exist around an altitude of 70 km. Unlike the terrestrial case, where the metallic ions are formed via charge-exchange with the ambient ions, Mg(+) in the Martian atmosphere is produced by photoionization. Nevertheless, the predicted metal layer peak densities for Earth and Mars are similar. Diffusion solutions, such as those presented here, should be a good approximation of the metallic ions in regions where the magnetic field is negligible and may provide a significant contribution to the nightside ionosphere. The low ultraviolet absorption of the Martian atmosphere may make Mars an excellent laboratory in which to study meteoric ablation. Resonance lines not seen in the spectra of terrestrial meteors may be visible to a surface observatory in the Martian highlands.

Grebowsky, J. M.; Pesnell, W. D.

1999-01-01

316

Tandem Mass Spectrometry of Heparan Sulfate Negative Ions: Sulfate Loss Patterns and Chemical Modification Methods for Improvement of Product Ion Profiles  

NASA Astrophysics Data System (ADS)

Heparan sulfate (HS) is a polysaccharide modified with sulfation, acetylation, and epimerization that enable its binding with protein ligands and regulation of important biological processes. Tandem mass spectrometry has been employed to sequence linear biomolecules e.g., proteins and peptides. However, its application in structural characterization of HS is limited due to the neutral loss of sulfate (SO3) during collisional induced dissociation (CID). In this report, we studied the dissociation patterns of HS disaccharides and demonstrate that the N-sulfate (N-S) bond is especially facile during CID. We identified factors that influence the propensities of such losses from precursor ions and proposed a Free Proton Index (FPI) to help select ions that are able to produce meaningful backbone dissociations. We then investigated the thermodynamics and kinetics of SO3 loss from sulfates that are protonated, deprotonated, and metal-adducted using density functional theory computations. The calculations showed that sulfate loss from a protonated site was much more facile than that from a deprotonated or metal-adducted site. Further, the loss of SO3 from N-sulfate was energetically favored by 3-8 kcal/mol in transition states relative to O-sulfates, making it more prone to this process by a substantial factor. In order to reduce the FPI, representing the number of labile sulfates in HS native chains and oligosaccharides, we developed a series of chemical modifications to selectively replace the N-sulfates of the glucosamine with deuterated acetyl group. These modifications effectively reduced the sulfate density on the HS oligosaccharides and generated considerably more backbone dissociation using on-line LC/tandem MS.

Shi, Xiaofeng; Huang, Yu; Mao, Yang; Naimy, Hicham; Zaia, Joseph

2012-09-01

317

Quorum-sensing cross talk: isolation and chemical characterization of cyclic dipeptides from Pseudomonas aeruginosa and other gram-negative bacteria.  

PubMed

In cell-free Pseudomonas aeruginosa culture supernatants, we identified two compounds capable of activating an N-acylhomoserine lactone (AHL) biosensor. Mass spectrometry and NMR spectroscopy revealed that these compounds were not AHLs but the diketopiperazines (DKPs), cyclo(DeltaAla-L-Val) and cyclo(L-Pro-L-Tyr) respectively. These compounds were also found in cell-free supernatants from Proteus mirabilis, Citrobacter freundii and Enterobacter agglomerans [cyclo(DeltaAla-L-Val) only]. Although both DKPs were absent from Pseudomonas fluorescens and Pseudomonas alcaligenes, we isolated, from both pseudomonads, a third DKP, which was chemically characterized as cyclo(L-Phe-L-Pro). Dose-response curves using a LuxR-based AHL biosensor indicated that cyclo(DeltaAla-L-Val), cyclo(L-Pro-L-Tyr) and cyclo(L-Phe-L-Pro) activate the biosensor in a concentration-dependent manner, albeit at much higher concentrations than the natural activator N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C6-HSL). Competition studies showed that cyclo(DeltaAla-L-Val), cyclo(L-Pro-L-Tyr) and cyclo(L-Phe-L-Pro) antagonize the 3-oxo-C6-HSL-mediated induction of bioluminescence, suggesting that these DKPs may compete for the same LuxR-binding site. Similarly, DKPs were found to be capable of activating or antagonizing other LuxR-based quorum-sensing systems, such as the N-butanoylhomoserine lactone-dependent swarming motility of Serratia liquefaciens. Although the physiological role of these DKPs has yet to be established, their activity suggests the existence of cross talk among bacterial signalling systems. PMID:10510239

Holden, M T; Ram Chhabra, S; de Nys, R; Stead, P; Bainton, N J; Hill, P J; Manefield, M; Kumar, N; Labatte, M; England, D; Rice, S; Givskov, M; Salmond, G P; Stewart, G S; Bycroft, B W; Kjelleberg, S; Williams, P

1999-09-01

318

Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets. V. Alfvén Ionization  

NASA Astrophysics Data System (ADS)

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfvén ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization (>=10-7) that they constitute plasmas. We outline the criteria required for Alfvén ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfvén ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10-6-1 can be obtained as a result of Alfvén ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H2, or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfvén ionization may also be applicable to other astrophysical environments such as protoplanetary disks.

Stark, C. R.; Helling, Ch.; Diver, D. A.; Rimmer, P. B.

2013-10-01

319

Molecular ionization from carbon nanotube paper.  

PubMed

Ambient ionization is achieved by spraying from a carbon nanotube (CNT)-impregnated paper surface under the influence of small voltages (?3?V). Organic molecules give simple high-quality mass spectra without fragmentation in the positive or negative ion modes. Conventional field ionization is ruled out, and it appears that field emission of microdroplets occurs. Microscopic examination of the CNT paper confirms that the nanoscale features at the paper surface are responsible for the high electric fields. Raman spectra imply substantial current flows in the nanotubes. The performance of this analytical method was demonstrated for a range of volatile and nonvolatile compounds and a variety of matrices. PMID:24643979

Narayanan, Rahul; Sarkar, Depanjan; Cooks, R Graham; Pradeep, Thalappil

2014-06-01

320

Chemical profile of meta-chlorophenylpiperazine (m-CPP) in ecstasy tablets by easy ambient sonic-spray ionization, X-ray fluorescence, ion mobility mass spectrometry and NMR.  

PubMed

Meta-chlorophenylpiperazine (m-CPP) is a new illicit drug that has been sold as ecstasy tablets. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) and X-ray fluorescence spectrometry (XRF) are shown to provide relatively simple and selective screening tools to distinguish m-CPP tablets from tablets containing amphetamines (mainly 3,4-methylenedioxymethamphetamine (MDMA)). EASI-MS detects the active ingredients in their protonated forms: [m-CPP + H](+) of m/z 197, [MDMA + H](+) of m/z 194, and [2MDMA + HCl + H](+) of m/z 423 and other ions from excipients directly on the tablet surface, providing distinct chemical fingerprints. XRF identifies Cl, K, Ca, Fe, and Cu as inorganic ingredients present in the m-CPP tablets. In contrast, higher Cl concentrations and a more diverse set of elements (P, Cl, Ca, Fe, Cu, Zn, Pt, V, Hf, Ti, Pt, and Zr) were found in MDMA tablets. Principal component analysis applied to XRF data arranged samples in three groups: m-CPP tablets (four samples), MDMA tablets (twenty three samples), and tablets with no active ingredients (three samples). The EASI-MS and XRF techniques were also evaluated to quantify m-CPP in ecstasy tablets, with concentrations ranging from 4 to 40 mg of m-CPP per tablets. The m-CPP could only be differentiated from its isomers (o-CPP and for the three isomers p-CPP) by traveling wave ion mobility mass spectrometry and NMR measurements. PMID:21475947

Romão, Wanderson; Lalli, Priscila M; Franco, Marcos F; Sanvido, Gustavo; Schwab, Nicolas V; Lanaro, Rafael; Costa, José Luiz; Sabino, Bruno D; Bueno, Maria Izabel M S; de Sa, Gilberto F; Daroda, Romeu J; de Souza, Vanderlea; Eberlin, Marcos N

2011-07-01

321

Quantification of ?-carotene, retinol, retinyl acetate and retinyl palmitate in enriched fruit juices using dispersive liquid-liquid microextraction coupled to liquid chromatography with fluorescence detection and atmospheric pressure chemical ionization-mass spectrometry.  

PubMed

A detailed optimization of dispersive liquid-liquid microextraction (DLLME) was carried out for developing liquid chromatographic (HPLC) techniques, using both fluorescence and atmospheric pressure chemical ionization mass spectrometric (APCI-MS) detection, for the simultaneous analysis of preforms of vitamin A: retinol (R), retinyl acetate (RA), retinyl palmitate (RP) and ?-carotene (?-C). The HPLC analyses were carried out using a mobile phase composed of methanol and water, with gradient elution. The APCI-MS and fluorescence spectra permitted the correct identification of compounds in the analyzed samples. Parameters affecting DLLME were optimized using 2 mL of methanol (disperser solvent) containing 150 ?L carbon tetrachloride (extraction solvent). The precision ranged from 6% to 8% (RSD) and the limits of detection were between 0.03 and 1.4 ng mL(-1), depending on the compound. The enrichment factor values were in the 21-44 range. Juice samples were analyzed without saponification and no matrix effect was found when using fluorescence detection, so calibration was possible with aqueous standards. However, a matrix effect appeared with APCI-MS, in which case it was necessary to apply matrix-matched calibration. There was great variability in the forms of vitamin A present in the juices, the most abundant ester being retinyl acetate (0.04 to 3.4 ?g mL(-1)), followed by the amount of retinol (0.01 to 0.16 ?g mL(-1)), while retinyl palmitate was not detected, except in the milk-containing juice, in which RP was the main form. The representative carotenoid ?-carotene was present in the orange, peach, mango and multifruit juices in high amounts. The method was validated using two certified reference materials. PMID:23290361

Viñas, Pilar; Bravo-Bravo, María; López-García, Ignacio; Hernández-Córdoba, Manuel

2013-02-01

322

Laser Ablation Electrospray Ionization for Atmospheric Pressure, in Vivo, and Imaging Mass  

E-print Network

Laser Ablation Electrospray Ionization for Atmospheric Pressure, in Vivo, and Imaging Mass. For example, atmospheric pressure infrared MALDI (AP IR-MALDI), capable of producing ions from small ionization (DESI),5 desorption atmospheric pressure chemical ionization (DAPCI),6 and matrix- assisted laser

Vertes, Akos

323

Matrix Assisted Ionization in Vacuum, a Sensitive and Widely Applicable Ionization Method for Mass Spectrometry  

NASA Astrophysics Data System (ADS)

An astonishingly simple new method to produce gas-phase ions of small molecules as well as proteins from the solid state under cold vacuum conditions is described. This matrix assisted ionization vacuum (MAIV) mass spectrometry (MS) method produces multiply charged ions similar to those that typify electrospray ionization (ESI) and uses sample preparation methods that are nearly identical to matrix-assisted laser desorption/ionization (MALDI). Unlike these established methods, MAIV does not require a laser or voltage for ionization, and unlike the recently introduced matrix assisted ionization inlet method, does not require added heat. MAIV-MS requires only introduction of a crystalline mixture of the analyte incorporated with a suitable small molecule matrix compound such as 3-nitrobenzonitrile directly to the vacuum of the mass spectrometer. Vacuum intermediate pressure MALDI sources and modified ESI sources successfully produce ions for analysis by MS with this method. As in ESI-MS, ion formation is continuous and, without a laser, little chemical background is observed. MAIV, operating from a surface offers the possibility of significantly improved sensitivity relative to atmospheric pressure ionization because ions are produced in the vacuum region of the mass spectrometer eliminating losses associated with ion transfer from atmospheric pressure to vacuum. Mechanistic aspects and potential applications for this new ionization method are discussed.

Trimpin, Sarah; Inutan, Ellen D.

2013-05-01

324

Measurement of the first ionization potential of astatine by laser ionization spectroscopy  

E-print Network

The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of smallest quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.317510(8) eV. New ab initio calculations were performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of super-heavy element 117, the heaviest homologue of astatine.

Rothe, S; Antalic, S; Borschevsky, A; Capponi, L; Cocolios, T E; De Witte, H; Eliav, E; Fedorov, D V; Fedosseev, V N; Fink, D A; Fritzsche, S; Ghys, L; Huyse, M; Imai, N; Kaldor, U; Kudryavtsev, Yu; Köster, U; Lane, J; Lassen, J; Liberati, V; Lynch, K M; Marsh, B A; Nishio, K; Pauwels, D; Pershina, V; Popescu, L; Procter, T J; Radulov, D; Raeder, S; Rajabali, M M; Rapisarda, E; Rossel, R E; Sandhu, K; Seliverstov, M D; Sjödin, A M; Van den Bergh, P; Van Duppen, P; Venhart, M; Wakabayashi, Y; Wendt K D A

2013-01-01

325

Measurement of the first ionization potential of astatine by laser ionization spectroscopy.  

PubMed

The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine. PMID:23673620

Rothe, S; Andreyev, A N; Antalic, S; Borschevsky, A; Capponi, L; Cocolios, T E; De Witte, H; Eliav, E; Fedorov, D V; Fedosseev, V N; Fink, D A; Fritzsche, S; Ghys, L; Huyse, M; Imai, N; Kaldor, U; Kudryavtsev, Yuri; Köster, U; Lane, J F W; Lassen, J; Liberati, V; Lynch, K M; Marsh, B A; Nishio, K; Pauwels, D; Pershina, V; Popescu, L; Procter, T J; Radulov, D; Raeder, S; Rajabali, M M; Rapisarda, E; Rossel, R E; Sandhu, K; Seliverstov, M D; Sjödin, A M; Van den Bergh, P; Van Duppen, P; Venhart, M; Wakabayashi, Y; Wendt, K D A

2013-01-01

326

Measurement of the first ionization potential of astatine by laser ionization spectroscopy  

NASA Astrophysics Data System (ADS)

The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine.

Rothe, S.; Andreyev, A. N.; Antalic, S.; Borschevsky, A.; Capponi, L.; Cocolios, T. E.; de Witte, H.; Eliav, E.; Fedorov, D. V.; Fedosseev, V. N.; Fink, D. A.; Fritzsche, S.; Ghys, L.; Huyse, M.; Imai, N.; Kaldor, U.; Kudryavtsev, Yuri; Köster, U.; Lane, J. F. W.; Lassen, J.; Liberati, V.; Lynch, K. M.; Marsh, B. A.; Nishio, K.; Pauwels, D.; Pershina, V.; Popescu, L.; Procter, T. J.; Radulov, D.; Raeder, S.; Rajabali, M. M.; Rapisarda, E.; Rossel, R. E.; Sandhu, K.; Seliverstov, M. D.; Sjödin, A. M.; van den Bergh, P.; van Duppen, P.; Venhart, M.; Wakabayashi, Y.; Wendt, K. D. A.

2013-05-01

327

Pharmacokinetics screening for multi-components absorbed in the rat plasma after oral administration of traditional Chinese medicine Flos Lonicerae Japonicae-Fructus Forsythiae herb couple by sequential negative and positive ionization ultra-high-performance liquid chromatography/tandem triple quadrupole mass spectrometric detection.  

PubMed

The current study aims to investigate the pharmacokinetics of multi-components (caffeic acid, quinic acid, genistein, luteolin, quercetin, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, arctigenin, genistin, luteoloside, astragalin, hyperoside, isoquercitrin, 3,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, rutin, loganin, pinoresinol-?-d-glucoside, phillyrin, isoforsythoside, forsythoside A and forsythoside B) following oral administration of Flos Lonicerae Japonicae-Fructus Forsythiae herb couple in rats. A rapid and sensitive UPLC-ESI-MS/MS with sequential positive and negative ionization modes was developed to determine the 23 absorbed ingredients using one sample preparation combined with three chromatographic conditions in rat plasma. After mixing with internal standard (IS) (tinidazole and chloramphenicol), samples were pretreated by liquid-liquid extraction (LLE) with n-butyl alcohol/ethyl acetate (1:1, v/v). The separations for pinoresinol-?-d-glucoside, phillyrin, isoforsythoside, forsythoside A and forsythoside B were performed on an ACQUITY UPLC BEH C18 column (100mm×2.1mm, 1.7?m) with acetonitrile/methanol (4:1, v/v)-water as mobile phase. For analyzing quinic acid, an ACQUITY UPLC HSS T3 column (100mm×2.1mm, 1.8?m) was applied with acetonitrile/methanol (4:1, v/v)-0.01% formic acid as mobile phase after dilution up to 25-fold. The same column was applied to the other components with acetonitrile/methanol (4:1, v/v)-0.4% formic acid as mobile phase. The method validation results demonstrated that the proposed method was sensitive, specific and reliable, which was successfully applied to the pharmacokinetic study of the multi-components after oral administration of Flos Lonicerae Japonicae-Fructus Forsythiae herb couple. PMID:25533397

Zhou, Wei; Tam, Kin Y; Meng, Minxin; Shan, Jinjun; Wang, Shouchuan; Ju, Wenzheng; Cai, Baochang; Di, Liuqing

2015-01-01

328

Determination of bile acids in pig liver, pig kidney and bovine liver by gas chromatography-chemical ionization tandem mass spectrometry with total ion chromatograms and extraction ion chromatograms.  

PubMed

An effective method has been developed for quantitative determination of six bile acids including lithocholic acid (LCA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA), hydodeoxycholic acid (HDCA), cholic acid (CA) and ursodeoxycholic acid (UDCA) in biological tissues including pig liver, pig kidney and bovine liver by gas chromatography-chemical ionization/tandem mass spectrometry (GC-CI/MS/MS). Camphor-10-sulphonic acid (CSA) was proposed as effective catalyst for bile acid derivatization. Reactions were accelerated ultrasonically. The effects of different catalysts and reaction times on derivatization efficiency were evaluated and optimized. Bile acids were determined as methyl ester-trimethylsilyl ether and methyl ester-acetate derivatives. The efficiency of trimethylsilylation and acetylation was evaluated. Trimethylsilylation was done with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) as the trimethylsilyl donating reagent in a ultrasonic bath for 20 min. Acetylation was done in pyridine with acetic anhydride at 40-45°C for 4 h. The former reaction was faster than the latter. Thus, trimethylsilylation was employed for the quantitative analysis. Negligible interferences from sterols in biological matrices were observed when the biological samples were treated with solid phase extraction before GC-CI/MS/MS. The linearity, reproducibility, detection limit and recovery were evaluated under the optimized conditions. Satisfactory results were obtained when bile acid derivatives of LCA, CDCA, HDCA, and UDCA were determined with total ion chromatograms (TIC) while DCA and CA were determined with extracted ion chromatograms (EIC), respectively. The detection limits (S/N=3) for six bile acids in biological tissues were ranging from 0.40 to 1.6 ng/mL and the recoveries indicated that the proposed method was feasible for the determination of trace bile acids in the biological samples studied. The experimental results for the animal tissues purchased from five different markets were compared. Interestingly, all of the six bile acids were present in pig liver while only the dihydroxy bile acids, DCA, CDCA and HDCA were found in pig kidney. In addition to DCA and CDCA, trihydroxy bile acid, CA, are the major bile acids in bovine liver. PMID:21176836

Tsai, Suh-Jen Jane; Zhong, Yao-Shen; Weng, Jen-Feng; Huang, Hsiu-Hua; Hsieh, Pei-Yin

2011-01-21

329

Flowing afterglow selected ion flow tube (FA-SIFT) study of ion/molecule reactions in support of the detection of biogenic alcohols by medium-pressure chemical ionization mass spectrometry techniques  

NASA Astrophysics Data System (ADS)

This article deals with the validation of and first measurements with a newly constructed flowing afterglow selected ion flow tube (FA-SIFT) instrument. All reactions were studied in He buffer gas at a pressure of 1.43 hPa and a temperature of 298 K. The validation consisted of the study of the gas-phase ion/molecule reactions of methanol and ethanol (M) with the reactant ions H3O+.(H2O)n (n = 0-3), MH+, M2H+, and MH+.H2O and the reactions of MH+ with H2O. Obtained results are compared with available literature data and with calculated collision rate constants. The validated FA-SIFT has subsequently been used to characterize the reactions of the unsaturated biogenic alcohols 2-methyl-3-buten-2-ol, 1-penten-3-ol, cis-3-hexen-1-ol and trans-2-hexen-1-ol (ROH) with H3O+.(H2O)n (n = 0-3) as well as the secondary reactions of the H3O+/ROH product ions with H2O (hydration) and ROH in view of their accurate quantification in ambient air samples with medium-pressure chemical ionization mass spectrometry (CIMS) instrumentation using H3O+ reactant ions. Whereas water elimination following proton transfer was found to be the main mechanism for all H3O+/ROH reactions studied and for the H3O+.H2O/trans-2-hexen-1-ol reaction, all other H3O+.(H2O)n/ROH (n = 1, 2) reactions proceeded by multiple reaction mechanisms. H3O+.(H2O)3 reactions proceeded mainly (C6 alcohols) or exclusively (C5 alcohols) by ligand switching followed by water elimination. Hydration of the H3O+/ROH product ions was observed whenever they contained oxygen. The secondary reactions with ROH were also found to proceed by multiple reaction pathways.

Dhooghe, F.; Amelynck, C.; Rimetz-Planchon, J.; Schoon, N.; Vanhaecke, F.

2009-08-01

330

40 CFR 52.122 - Negative declarations.  

Code of Federal Regulations, 2012 CFR

...submitted negative declarations for volatile organic compound source categories to satisfy...Flatwood Paneling, Pharmaceuticals and Cosmetic Manufacturing Operations, Rubber Tire...Ship Building and Repair, Synthetic Organic Chemical Manufacturing Industry...

2012-07-01

331

Ionizing potential waves and high-voltage breakdown streamers.  

NASA Technical Reports Server (NTRS)

The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.

Albright, N. W.; Tidman, D. A.

1972-01-01

332

A surface ionization source  

E-print Network

The main part of the work described herein is the development and testing of a surface ionization source for use on a collinear fast beam laser spectroscopy apparatus. A description of the previously existing fast beam apparatus is given...

Buzatu, Daniel J.

2012-06-07

333

Negative ion source with hollow cathode discharge plasma  

DOEpatents

A negative ion source of the type where negative ions are formed by bombarding a low-work-function surface with positive ions and neutral particles from a plasma, wherein a highly ionized plasma is injected into an anode space containing the low-work-function surface. The plasma is formed by hollow cathode discharge and injected into the anode space along the magnetic field lines. Preferably, the negative ion source is of the magnetron type.

Hershcovitch, Ady (Mt. Sinai, NY); Prelec, Krsto (Setauket, NY)

1983-01-01

334

Negative ion source with hollow cathode discharge plasma  

DOEpatents

A negative ion source of the type where negative ions are formed by bombarding a low-work-function surface with positive ions and neutral particles from a plasma, wherein a highly ionized plasma is injected into an anode space containing the low-work-function surface is described. The plasma is formed by hollow cathode discharge and injected into the anode space along the magnetic field lines. Preferably, the negative ion source is of the magnetron type.

Hershcovitch, A.; Prelec, K.

1980-12-12

335

Ionizing Radiation and Its Risks  

PubMed Central

Penetrating ionizing radiation fairly uniformly puts all exposed molecules and cells at approximately equal risk for deleterious consequences. Thus, the original deposition of radiation energy (that is, the dose) is unaltered by metabolic characteristics of cells and tissue, unlike the situation for chemical agents. Intensely ionizing radiations, such as neutrons and alpha particles, are up to ten times more damaging than sparsely ionizing sources such as x-rays or gamma rays for equivalent doses. Furthermore, repair in cells and tissues can ameliorate the consequences of radiation doses delivered at lower rates by up to a factor of ten compared with comparable doses acutely delivered, especially for somatic (carcinogenic) and genetic effects from x- and gamma-irradiation exposure. Studies on irradiated laboratory animals or on people following occupational, medical or accidental exposures point to an average lifetime fatal cancer risk of about 1 × 10-4 per rem of dose (100 per 106 person-rem). Leukemia and lung, breast and thyroid cancer seem more likely than other types of cancer to be produced by radiation. Radiation exposures from natural sources (cosmic rays and terrestrial radioactivity) of about 0.1 rem per year yield a lifetime cancer risk about 0.1 percent of the normally occurring 20 percent risk of cancer death. An increase of about 1 percent per rem in fatal cancer risk, or 200 rem to double the “background” risk rate, is compared with an estimate of about 100 rem to double the genetic risk. Newer data suggest that the risks for low-level radiation are lower than risks estimated from data from high exposures and that the present 5 rem per year limit for workers is adequate. PMID:6761969

Goldman, Marvin

1982-01-01

336

Dielectric barrier discharge ionization for liquid chromatography/mass spectrometry.  

PubMed

An atmospheric pressure microplasma ionization source based on a dielectric barrier discharge with a helium plasma cone outside the electrode region has been developed for liquid chromatography/mass spectrometry (LC/MS). For this purpose, the plasma was realized in a commercial atmospheric pressure ionization source. Dielectric barrier discharge ionization (DBDI) was compared to conventional electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) in the positive ionization mode. Therefore, a heterogeneous compound library was investigated that covered polar compounds such as amino acids, water-soluble vitamins, and nonpolar compounds like polycyclic aromatic hydrocarbons and functionalized hydrocarbons. It turned out that DBDI can be regarded as a soft ionization technique characterized by only minor fragmentation similar to APCI. Mainly protonated molecules were detected. Additionally, molecular ions were observed for polycyclic aromatic hydrocarbons and derivatives thereof. During DBDI, adduct formation with acetonitrile occurred. For aromatic compounds, addition of one to four oxygen atoms and to a smaller extend one nitrogen and oxygen was observed which delivered insight into the complexity of the ionization processes. In general, compounds covering a wider range of polarities can be ionized by DBDI than by ESI. Furthermore, limits of detection compared to APCI are in most cases equal or even better. PMID:19911793

Hayen, Heiko; Michels, Antje; Franzke, Joachim

2009-12-15

337

Ionization-based gas sensor using aligned MWCNTs array  

Microsoft Academic Search

Current gas sensors are mainly categorized into two modes of operation; chemical type operating by gas adsorption and physical type using ionization method. Chemical type conductivity-based gas detectors are large in size, they operate at high temperatures, and their response time is slow. Moreover most of them are only capable of detecting single type gases due to their low selectivity.

A. R. Kermany; N. M. Mohamed; B. S. Mahinder Singh

2010-01-01

338

Fuel cell with ionization membrane  

NASA Technical Reports Server (NTRS)

A fuel cell is disclosed comprising an ionization membrane having at least one area through which gas is passed, and which ionizes the gas passing therethrough, and a cathode for receiving the ions generated by the ionization membrane. The ionization membrane may include one or more openings in the membrane with electrodes that are located closer than a mean free path of molecules within the gas to be ionized. Methods of manufacture are also provided.

Hartley, Frank T. (Inventor)

2007-01-01

339

Prompt ionization in the CRIT II barium releases. [Critical Ionization Tests  

NASA Technical Reports Server (NTRS)

Observations of electron and ion distributions inside a fast neutral barium jet in the ionosphere show significant fluxes within 4 km of release, presumably related to beam plasma instability processes involved in the Critical Ionization Velocity (CIV) effect. Electron fluxes exceeding 5 x 10 exp 12/sq cm-str-sec-keV were responsible for ionizing both the streaming barium and ambient oxygen. Resulting ion fluxes seem to be consistent with 1-2 percent ionization of the fast barium, as reported by optical observations, although the extended spatial distribution of the optically observed ions is difficult to reconcile with the in situ observations. When the perpendicular velocity of the neutrals falls below critical values, these processes shut off. Although these observations resemble the earlier Porcupine experimental results (Haerendel, 1982), theoretical understanding of the differences between these data and that of earlier negative experiments is still lacking.

Torbert, R. B.; Kletzing, C. A.; Liou, K.; Rau, D.

1992-01-01

340

Bohr effect of human hemoglobin A: magnitude of negative contributions determined by the equilibrium between two tertiary structures.  

PubMed

We have measured the affinity of the CysF9[93]? sulfhydryl group of human deoxyhemoglobin and oxyhemoglobin for 5,5'-dithiobis(2-nitrobenzoate), DTNB, between pH ?5.6 and 9 in order to understand the basis of the reported reduction of the Bohr effect induced by chemical modification of the sulfhydryl. We analyzed the results quantitatively on the basis of published data indicating that the sulfhydryl exists in two conformations that are coupled to the transition between two tertiary structures of hemoglobin in dynamic equilibrium. Our analyses show that the ionizable groups linked to the DTNB reaction have lower pKas of ionization in deoxyhemoglobin compared to oxyhemoglobin. So these ionizable groups should make negative contributions to the Bohr effect. We identify these groups as HisNA2[2]?, HisEF1[77]? and HisH21[143]?. We provide explanations for the finding that hemoglobin, chemically modified at CysF9[93]?, has a lower Bohr effect and a higher oxygen affinity than unmodified hemoglobin. PMID:24824171

Okonjo, Kehinde O; Olatunde, Abimbola M; Fodeke, Adedayo A; Babalola, J Oyebamiji

2014-06-01

341

Relativistic runaway ionization fronts.  

PubMed

We investigate the first example of self-consistent impact ionization fronts propagating at relativistic speeds and involving interacting, high-energy electrons. These fronts, which we name relativistic runaway ionization fronts, show remarkable features such as a bulk speed within less than one percent of the speed of light and the stochastic selection of high-energy electrons for further acceleration, which leads to a power-law distribution of particle energies. A simplified model explains this selection in terms of the overrun of Coulomb-scattered electrons. Appearing as the electromagnetic interaction between electrons saturates the exponential growth of a relativistic runaway electron avalanche, relativistic runaway ionization fronts may occur in conjunction with terrestrial gamma-ray flashes and thus explain recent observations of long, power-law tails in the terrestrial gamma-ray flash energy spectrum. PMID:24580462

Luque, A

2014-01-31

342

Relativistic Runaway Ionization Fronts  

NASA Astrophysics Data System (ADS)

We investigate the first example of self-consistent impact ionization fronts propagating at relativistic speeds and involving interacting, high-energy electrons. These fronts, which we name relativistic runaway ionization fronts, show remarkable features such as a bulk speed within less than one percent of the speed of light and the stochastic selection of high-energy electrons for further acceleration, which leads to a power-law distribution of particle energies. A simplified model explains this selection in terms of the overrun of Coulomb-scattered electrons. Appearing as the electromagnetic interaction between electrons saturates the exponential growth of a relativistic runaway electron avalanche, relativistic runaway ionization fronts may occur in conjunction with terrestrial gamma-ray flashes and thus explain recent observations of long, power-law tails in the terrestrial gamma-ray flash energy spectrum.

Luque, A.

2014-01-01

343

Dow and Kaw,eff vs. Kow and K°aw: Acid\\/base ionization effects on partitioning properties and screening commercial chemicals for long-range transport and bioaccumulation potential  

Microsoft Academic Search

A set of 543 ionizable commercial organic compounds with various acid\\/base functionalities and experimental octanol-water partitioning coefficients (log Kow) were obtained from the Canadian Domestic Substances List. Corresponding pH-dependent octanol-water distribution coefficients (log Dow) and air-water partitioning coeffients (log Kaw,eff) were estimated using the SPARC software program, as were log Kow and log K°aw values for the neutral forms of

Sierra Rayne; Kaya Forest

2010-01-01

344

Negative Pressure Wound Therapy  

PubMed Central

Executive Summary Objective This review was conducted to assess the effectiveness of negative pressure wound therapy. Clinical Need: Target Population and Condition Many wounds are difficult to heal, despite medical and nursing care. They may result from complications of an underlying disease, like diabetes; or from surgery, constant pressure, trauma, or burns. Chronic wounds are more often found in elderly people and in those with immunologic or chronic diseases. Chronic wounds may lead to impaired quality of life and functioning, to amputation, or even to death. The prevalence of chronic ulcers is difficult to ascertain. It varies by condition and complications due to the condition that caused the ulcer. There are, however, some data on condition-specific prevalence rates; for example, of patients with diabetes, 15% are thought to have foot ulcers at some time during their lives. The approximate community care cost of treating leg ulcers in Canada, without reference to cause, has been estimated at upward of $100 million per year. Surgically created wounds can also become chronic, especially if they become infected. For example, the reported incidence of sternal wound infections after median sternotomy is 1% to 5%. Abdominal surgery also creates large open wounds. Because it is sometimes necessary to leave these wounds open and allow them to heal on their own (secondary intention), some may become infected and be difficult to heal. Yet, little is known about the wound healing process, and this makes treating wounds challenging. Many types of interventions are used to treat wounds. Current best practice for the treatment of ulcers and other chronic wounds includes debridement (the removal of dead or contaminated tissue), which can be surgical, mechanical, or chemical; bacterial balance; and moisture balance. Treating the cause, ensuring good nutrition, and preventing primary infection also help wounds to heal. Saline or wet-to-moist dressings are reported as traditional or conventional therapy in the literature, although they typically are not the first line of treatment in Ontario. Modern moist interactive dressings are foams, calcium alginates, hydrogels, hydrocolloids, and films. Topical antibacterial agents—antiseptics, topical antibiotics, and newer antimicrobial dressings—are used to treat infection. The Technology Being Reviewed Negative pressure wound therapy is not a new concept in wound therapy. It is also called subatmospheric pressure therapy, vacuum sealing, vacuum pack therapy, and sealing aspirative therapy. The aim of the procedure is to use negative pressure to create suction, which drains the wound of exudate (i.e., fluid, cells, and cellular waste that has escaped from blood vessels and seeped into tissue) and influences the shape and growth of the surface tissues in a way that helps healing. During the procedure, a piece of foam is placed over the wound, and a drain tube is placed over the foam. A large piece of transparent tape is placed over the whole area, including the healthy tissue, to secure the foam and drain the wound. The tube is connected to a vacuum source, and fluid is drawn from the wound through the foam into a disposable canister. Thus, the entire wound area is subjected to negative pressure. The device can be programmed to provide varying degrees of pressure either continuously or intermittently. It has an alarm to alert the provider or patient if the pressure seal breaks or the canister is full. Negative pressure wound therapy may be used for patients with chronic and acute wounds; subacute wounds (dehisced incisions); chronic, diabetic wounds or pressure ulcers; meshed grafts (before and after); or flaps. It should not be used for patients with fistulae to organs/body cavities, necrotic tissue that has not been debrided, untreated osteomyelitis, wound malignancy, wounds that require hemostasis, or for patients who are taking anticoagulants. Review Strategy The inclusion criteria were as follows: Randomized controlled trial (RCT) with a sample size of 20 or more Human s

2006-01-01

345

Theoretical study on structural effects of polymer ionization for EUV resist  

NASA Astrophysics Data System (ADS)

We studied the ionization of polymer for extreme ultraviolet (EUV) resist. Quantum chemical calculation was performed. Upon EUV exposure to the polymer in a resist, the ionization of the polymer occurs and the secondary electrons generate. As the secondary electrons from the polymer cause the reaction of photoacid generator and the photoacid generates, the ionization of the polymer is a key for the sensitivity of resist for EUV. In this paper, the structural effects of polymer ionization was investigated. The acryl polymers with various pendant groups were compared. It was found that the stable condition of radical cation helps the ionization of the polymer.

Endo, M.; Tagawa, S.

2012-03-01

346

IONIZING RADIATION OF EGGS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Contamination of eggs and egg products by Salmonella is associated with a significant number of illnesses in the U.S. each year. Ionizing radiation can inactivate Salmonella on the egg surface, in the egg white, and in the yolk of shell eggs, and has been approved by the U.S. FDA at doses up to 3.0...

347

Alkali ionization detector  

DOEpatents

A calibration filament containing a sodium-bearing compound is included in combination with the sensing filament and ion collector plate of a sodium ionization detector to permit periodic generation of sodium atoms for the in-situ calibration of the detector.

Hrizo, John (Monroeville, PA); Bauerle, James E. (Plum Borough, PA); Witkowski, Robert E. (West Mifflin, PA)

1982-01-01

348

Precombustion ionization device  

Microsoft Academic Search

Precombustion ionization devices are disclosed for treating the vaporizable liquid fuel in internal combustion engines, including at least one foraminous member prepared from a catalytic metal having an oxide coating on the surface thereof. The foraminous member, or screen, is spaced from the carburetor and the engine intake of the internal combustion engine by means of a supporting gasket. The

J. B. Jr. Hicks; D. J. Hicks

1978-01-01

349

Avalanche Ionization and the Limiting Diameter of Filaments Induced by Light Pulses in Transparent Media  

Microsoft Academic Search

A limiting intensity is shown to exist for light propagation in transparent liquids and solids. In pure bulk materials it is determined by avalanche ionization over a wide range of pulse durations, wavelengths, and band gaps. The ionization rate per unit time is deduced from the thickness dependence of the dc breakdown. The negative real part of the index of

Eli Yablonovitch; N. Bloembergen

1972-01-01

350

ChemTeacher: Ionization Energy  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Ionization Energy page includes resources for teaching students about trends in ionization energy.

2011-01-01

351

Modulated voltage metastable ionization detector  

NASA Technical Reports Server (NTRS)

The output current from a metastable ionization detector (MID) is applied to a modulation voltage circuit. An adjustment is made to balance out the background current, and an output current, above background, is applied to an input of a strip chart recorder. For low level concentrations, i.e., low detected output current, the ionization potential will be at a maximum and the metastable ionization detector will operate at its most sensitive level. When the detected current from the metastable ionization detector increases above a predetermined threshold level, a voltage control circuit is activated which turns on a high voltage transistor which acts to reduce the ionization potential. The ionization potential applied to the metastable ionization detector is then varied so as to maintain the detected signal level constant. The variation in ionization potential is now related to the concentration of the constituent and a representative amplitude is applied to another input of said strip chart recorder.

Carle, G. C.; Kojiro, D. R.; Humphrey, D. E. (inventors)

1985-01-01

352

Ionization photophysics and spectroscopy of cyanoacetylene  

NASA Astrophysics Data System (ADS)

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11-15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC3N involves new aspects and new assignments of the vibrational components to excitation of the A2?+ and B2? states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B2? state of HC3N+. A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C2?+ state of HC3N+ at ?17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6-15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C-H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.

Leach, Sydney; Garcia, Gustavo A.; Mahjoub, Ahmed; Bénilan, Yves; Fray, Nicolas; Gazeau, Marie-Claire; Gaie-Levrel, François; Champion, Norbert; Schwell, Martin

2014-05-01

353

Nonlinear modulation of ionization waves  

Microsoft Academic Search

In order to investigate the nonlinear characteristics of ionization waves (moving-striations) in the positive column of glow discharge, a nonlinear modulation of ionization waves in the region of the Pupp critical current is analyzed by means of the reductive perturbation method. The modulation of ionization waves is described by a nonlinear Schroedinger type equation. The coefficients of the equation are

Naoaki Bekki

1981-01-01

354

Sentential Negation in English  

ERIC Educational Resources Information Center

This paper undertakes a detailed analysis of sentential negation in the English language with Chomsky's Government-Binding theory of Transformational Grammar as theoretical model. It distinguishes between constituent and sentential negation in English. The essay identifies the exact position of Negation phrase in an English clause structure. It…

Mowarin, Macaulay

2009-01-01

355

Ionization Models of Symbiotic Stars  

NASA Astrophysics Data System (ADS)

A model of a symbiotic system is outlined. The author presents evidence that the main ionization mechanism responsible for the symbiotic nebula is radiative and not collisional. If the ionizing radiation is due to accretion, the boundary layer between accreting star and disc provides the bulk of the ionizing photons. The possibility for distinguishing between different ionization sources are briefly discussed. C/N and O/N abundance ratios, calculated with the outlined ionization model places HM Sge, RS Oph, and T CrB among the novae and not among the symbiotic stars.

Nussbaumer, H.

356

Electrospray Ionization Mass Spectrometry  

SciTech Connect

Electrospray Ionization (ESI) is a process whereby gas phase ions are created from molecules in solution. As a solution exits a narrow tube in the presence of a strong electric field, an aerosol of charged droplets are is formed that produces gas phase ions as they it desolvates. ESI-MS comprises the creation of ions by ESI and the determination of their mass to charge ratio (m/z) by MS.

Kelly, Ryan T.; Marginean, Ioan; Tang, Keqi

2014-06-13

357

High brilliance negative ion and neutral beam source  

DOEpatents

A high brilliance mass selected (Z-selected) negative ion and neutral beam source having good energy resolution. The source is based upon laser resonance ionization of atoms or molecules in a small gaseous medium followed by charge exchange through an alkali oven. The source is capable of producing microampere beams of an extremely wide variety of negative ions, and milliampere beams when operated in the pulsed mode.

Compton, Robert N. (Oak Ridge, TN)

1991-01-01

358

Depression and ionizing radiation.  

PubMed

The objective of this at issue paper is the analysis of published data in correlation with the results of own research on the potential role of ionizing radiation in the genesis of depressive disorders. Depression is one of the most significant and long-term effect of the atomic bombings, nuclear testing and radiation emergences. The participants of the accident at the Chornobyl nuclear power plant increased prevalence of depression (18.0% and 13.1% in controls) and suicide rates. Depression is mainly observed in the structure of an organic mental disorder against cerebrovascular disease. The clinical pattern is dominated by asthenoadynamic and asthenoapathetic depression. Depressive disorders in radiation emergencies are multifactorial, that is the result of exposure to the complex psychogenic and radiological accident's factors, impact of traditional risk factors, somatic and neurological diseases, genetic predisposition, predisposition, etc. At the same time, exposure to ionizing radiation is a factor in the genesis of depression. This impact can be direct (to the Central Nervous System), and indirectly through the somatic and neurological abnormalities (multiorgan dysfunction) as well as by a variety of pathogenic mechanisms of ionizing radiation on the brain that have been discovered recently. It is strongly necessary analytical clinical and epidemiological studies with verification of depression and evidence-based establishment of the role of radiation and non-radiation risk factors. PMID:25191725

Loganovsky, K N; Vasilenko, Z L

2013-01-01

359

Functionalized pyrolytic highly oriented graphite polymer film for surface-assisted laser desorption/ionization mass spectrometry in environmental analysis.  

PubMed

The pyrolytic highly oriented graphite polymer film (PGS) was first employed to analyze low-mass analytes in environmental analysis by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). PGS is a synthetic uniform and highly oriented graphite polymer film with high thermal anisotropic conductivity. We have found that negative ion mode SALDI-MS using oxidized PGS (PGS-SALDI-MS) can be used to detect [M-H]- ions from perfluorooctanoic acid (PFOA) and other perfluoroalkylcarboxylic acids when the PGS surface is modified with the cationic polymer polyethyleneimine (PEI). The signal intensity of PFOA when employing the PEI modification showed a ten-fold increase over that obtained from desorption/ionization on porous silicon (DIOS). PFOA was quantified using PGS-SALDI-MS and the calibration curve showed a wide linear dynamic range of response (20-1000 ppb). The combination of atmospheric pressure ionization and PGS (AP-PGS-SALDI) showed greater signal intensity than vacuum PGS-SALDI for deprotonated PFOA. Several other environmentally important chemicals, including perfluoroalkylsulfonic acid, pentachlorophenol, bisphenol A, 4-hydroxy-2-chlorobiphenyl, and benzo[a]pyrene, were also successfully used to evaluate PGS-SALDI-MS. In addition, we found that nonafluoro-1-butanesulfonic acid was able to produce protonated peptides in positive ion PGS-SALDI-MS, but that perfluoropentanoic acid and trifluoroacetic acid were not. It is suggested that perfluoroalkylsulfonic acids are better protonating agents than perfluoroalkylcarboxylic acids in SALDI-MS. PMID:19757448

Kawasaki, Hideya; Takahashi, Naoyuki; Fujimori, Hiroki; Okumura, Kouji; Watanabe, Takehiro; Matsumura, Chisato; Takemine, Syusuke; Nakano, Takeshi; Arakawa, Ryuichi

2009-10-30

360

Atmospheric pressure ionization and liquid chromatography\\/mass spectrometry—together at last  

Microsoft Academic Search

The evolution of atmospheric pressure ionization techniques which are now routinely applied as liquid chromatograph\\/mass spectrometer\\u000a (LC\\/MS) interfaces is described. Electrospray and related methods, as well as atmospheric pressure chemical ionization combined\\u000a with the heated nebulizer interface, both began as specialized ionization techniques which became much more widely accepted\\u000a when combined with tandem mass spectrometry. Today, both are widely used

Bruce A. Thomson

1998-01-01

361

Dissociative ionization of biomolecules  

NASA Astrophysics Data System (ADS)

Dissociative ionization (DI) by electron impact plays a role in many different applications, including low-temperature plasma processing, the study of space and astrophysical plasmas, and the study of biological damages by high-energy radiation. In the present study, our goal is to understand the health hazard to humans from exposure to radiation during an extended space flight. DI by secondary electrons can damage the DNA, either directly by causing a DNA lesion, or indirectly by producing radicals and cations that attack the DNA. The theoretical model employed makes use of the fact that electronic motion is much faster than nuclear motion, allowing DI to be treated as a two-step process. The first step is electron-impact ionization resulting in a dissociative state of the molecular ion with the same geometry as the neutral molecule. In the second step the ion relaxes from the initial geometry and undergoes unimolecular dissociation. Thus the DI cross section is given by the product of the ionization cross section and the dissociation probability. For the ionization process we use the improved binary-encounter dipole (iBED) model. For unimolecular dissociation, we use the multiconfigurational self-consistent field (MCSCF) method to determine the minimum energy pathways to possible product channels. This model has been applied to study the DI of H_2O, NH_3, and CH_4, and the results are in good agreement with experiment. The DI from the low-lying channels of benzene has also been studied and the dissociation products are compared with photoionization measurements. The DI of the DNA bases guanine and cytosine are then discussed. Of the four DNA bases, guanine has the largest ionization cross section and cytosine has the smallest. The guanine radical cation is considered to be one of the precursors to the primary, direct-type lesions formed in DNA when it is irradiated. Comparison of DI products of guanine and cytosine will be made to understand the differences in their behavior upon irradiation.

Huo, Winifred

2004-09-01

362

Analysis of solvent dyes in refined petroleum products by electrospray ionization mass spectrometry  

USGS Publications Warehouse

Solvent dyes are used to color refined petroleum products to enable differentiation between gasoline, diesel, and jet fuels. Analysis for these dyes in the hydrocarbon product is difficult due to their very low concentrations in such a complex matrix. Flow injection analysis/electrospray ionization/mass spectrometry in both negative and positive mode was used to optimize ionization of ten typical solvent dyes. Samples of hydrocarbon product were analyzed under similar conditions. Positive electrospray ionization produced very complex spectra, which were not suitably specific for targeting only the dyes. Negative electrospray ionization produced simple spectra because aliphatic and aromatic moieties were not ionized. This enabled screening for a target dye in samples of hydrocarbon product from a spill.

Rostad, C.E.

2010-01-01

363

Continuous flow-extractive desorption electrospray ionization: analysis from "non-electrospray ionization-friendly" solvents and related mechanism.  

PubMed

Due to their low polarities and dielectric constants, analytes in solvents such as hexane, chloroform, and ethyl acetate exhibit poor electrospray ionization (ESI) efficiency. These are deemed to be "non-ESI-friendly" solvents. Continuous flow extractive desorption electrospray ionization (CF-EDESI) is a novel ambient ionization technique that was recently developed in our group to manipulate protein charge distributions. Here we demonstrate its potential for ionizing analytes from non-ESI-friendly solvents. This feature makes CF-EDESI attractive to the general analytical community due to its apparent potential in lipidomics, normal phase separations, and hyphenation of mass spectrometry with HPLC-NMR systems. In this context, interest was subsequently initiated to discern mechanistic aspects of CF-EDESI. To achieve this, mechanistic experiments associated with a seemingly similar ambient ionization technique, extractive electrospray ionization (EESI), were emulated to compare CF-EDESI and EESI. Analysis of a series of fatty acids in multiple solvents in the negative ionization mode revealed differences between the two techniques. Whereas EESI has been previously shown to operate via extraction of analytes into the spray solvent, data presented here for CF-EDESI point toward a liquid-liquid mixing process to facilitate ionization. Further, a partial factorial design experiment was performed to evaluate the effects of different experimental variables on signal intensity. Sample flow rate was confirmed to be among the most significant factors to affect sensitivity. As a whole, the work presented provides greater insight into a new ambient ionization process, which exhibits expanded capabilities over conventional ESI; in this case, for direct analysis from non-ESI-friendly solvents. PMID:23498125

Li, Li; Yang, Samuel H; Lemr, Karel; Havlicek, Vladimir; Schug, Kevin A

2013-03-26

364

Neon and Argon optical emission lines in ionized gaseous nebulae: Implications and applications  

E-print Network

In this work we present a study of the strong optical collisional emission lines of Ne and Ar in an heterogeneous sample of ionized gaseous nebulae for which it is possible to derive directly the electron temperature and hence the chemical abundances of neon and argon. We calculate using a grid of photoionization models new ionization correction factors for these two elements and we study the behaviour of Ne/O and Ar/O abundance ratios with metallicity. We find a constant value for Ne/O, while there seems to be some evidence for the existence of negative radial gradients of Ar/O over the disks of some nearby spirals. We study the relation between the intensities of the emission lines of [NeIII] at 3869 \\AA and [OIII] at 4959 \\AA and 5007 \\AA. This relation can be used in empirical calibrations and diagnostic ratios extending their applicability to bluer wavelengths and therefore to samples of objects at higher redshifts. Finally, we propose a new diagnostic using [OII], [NeIII] and Hdelta emission lines to derive metallicities for galaxies at high z.

Enrique Perez-Montero; Guillermo F. Hagele; Thierry Contini; Angeles I. Diaz

2007-07-18

365

Liquid chromatography\\/atmospheric pressure ionization-mass spectrometry in drug metabolism studies  

Microsoft Academic Search

Thestudyofthemetabolicfateofdrugs isanessentialand importantpartofthedrug developmentprocess. The analysis of metabolites is a challenging task and several different analytical methods have been used in these studies. However, after the introduction of the atmospheric pressure ionization (API) technique, electrospray and atmospheric pressure chemical ionization, liquid chromatography\\/mass spectrometry (LC\\/MS) has become an important and widely used method in the analysis of metabolites owing to its

R. Kostiainen; T. Kotiaho; T. Kuuranne; S. Auriola

2003-01-01

366

Isomer discrimination of polycyclic aromatic hydrocarbons in the Murchison meteorite by resonant ionization  

E-print Network

Isomer discrimination of polycyclic aromatic hydrocarbons in the Murchison meteorite by resonant;Abstract We have used two-color resonant two-photon ionization (2C-R2PI) mass spectrometry to discriminate demonstrated isomer discrimination of PAHs by chemical ionization mass spectrometry with carbon dioxide

de Vries, Mattanjah S.

367

Spatially resolved thermal desorption/ionization coupled with mass spectrometry  

DOEpatents

A system and method for sub-micron analysis of a chemical composition of a specimen are described. The method includes providing a specimen for evaluation and a thermal desorption probe, thermally desorbing an analyte from a target site of said specimen using the thermally active tip to form a gaseous analyte, ionizing the gaseous analyte to form an ionized analyte, and analyzing a chemical composition of the ionized analyte. The thermally desorbing step can include heating said thermally active tip to above 200.degree. C., and positioning the target site and the thermally active tip such that the heating step forms the gaseous analyte. The thermal desorption probe can include a thermally active tip extending from a cantilever body and an apex of the thermally active tip can have a radius of 250 nm or less.

Jesse, Stephen; Van Berkel, Gary J; Ovchinnikova, Olga S

2013-02-26

368

Resonance ionization detection of combustion radicals  

SciTech Connect

Fundamental research on the combustion of halogenated organic compounds with emphasis on reaction pathways leading to the formation of chlorinated aromatic compounds and the development of continuous emission monitoring methods will assist in DOE efforts in the management and disposal of hazardous chemical wastes. Selective laser ionization techniques are used in this laboratory for the measurement of concentration profiles of radical intermediates in the combustion of chlorinated hydrocarbon flames. A new ultrasensitive detection technique, made possible with the advent of tunable VUV laser sources, enables the selective near-threshold photoionization of all radical intermediates in premixed hydrocarbon and chlorinated hydrocarbon flames.

Cool, T.A. [Cornell Univ., Ithaca, NY (United States)

1993-12-01

369

Negative-ion formation in the explosives RDX, PETN, and TNT using the Reversal Electron Attachment Detection (READ) technique  

NASA Technical Reports Server (NTRS)

In the search for high sensitivity and direct atmospheric sampling of trace species, techniques have been developed such as atmospheric-sampling, glow-discharge ionization (ASGDI), corona discharge, atmospheric pressure ionization (API), electron-capture detection (ECD), and negative-ion chemical ionization (NICI) that are capable of detecting parts-per-billion to parts-per-trillion concentrations of trace species. These techniques are based on positive- or negative-ion formation via charge-transfer to the target, or electron capture under multiple-collision conditions in a Maxwellian distribution of electron energies at the source temperature. One drawback of the high-pressure, corona- or glow-discharge devices is that they are susceptible to interferences either through indistinguishable product masses, or through undesired ion-molecule reactions. The ASGDI technique is relatively immune from such interferences, since at target concentrations of less than 1 ppm the majority of negative ions arises via electron capture rather than through ion-molecule chemistry. A drawback of the conventional ECD, and possibly of the ASGDI, is that they exhibit vanishingly small densities of electrons with energies in the range 0-10 millielectron volts (meV), as can be seen from a typical Maxwellian electron energy distribution function at T = 300 K. Slowing the electrons to these subthermal (less than 10 meV) energies is crucial, since the cross section for attachment of several large classes of molecules is known to increase to values larger than 10(exp -12) sq cm at near-zero electron energies. In the limit of zero energy these cross sections are predicted to diverge as epsilon(exp -1/2), where epsilon is the electron energy. In order to provide a better 'match' between the electron energy distribution function and attachment cross section, a new concept of attachment in an electrostatic mirror was developed. In this scheme, electrons are brought to a momentary halt by reversing their direction with electrostatic fields. At this turning point the electrons have zero or near-zero energy. A beam of target molecules is introduced, and the resultant negative ions extracted. This basic idea has been recently improved to allow for better reversal geometry, higher electron currents, lower backgrounds, and increased negative-ion extraction efficiency. We present herein application of the so-called reversal electron attachment detector (READ) to the study of negative-ion formation in the explosives molecules RDX, PETN, and TNT under single-collision conditions.

Chutijian, Ara; Boumsellek, S.; Alajajian, S. H.

1992-01-01

370

HIGH-SENSITIVITY THERMOSPRAY IONIZATION MASS SPECTROMETRY OF DYES  

EPA Science Inventory

A series of dyes belonging to different chemical classes have been analyzed by thermospray (TSP) ionization mass spectrometry using a modified source containing a wire-repeller. etection limits were determined and found to be in the range 0.05-20ng, which are lower by a factor of...

371

Heating the warm ionized medium  

NASA Technical Reports Server (NTRS)

If photoelectric heating by grains within the diffuse ionized component of the interstellar medium is 10 exp -25 ergs/s per H atom, the average value within diffuse H I regions, then grain heating equals or exceeds photoionization heating of the ionized gas. This supplemental heat source would obviate the need for energetic ionizing photons to balance the observed forbidden-line cooling and could be responsible in part for enhanced intensities of some of the forbidden lines.

Reynolds, R. J.; Cox, D. P.

1992-01-01

372

Study of the upper spinorbit state of the chloroiodomethane cation by mass-analyzed threshold ionization  

E-print Network

ionization Mina Lee, Myung Soo Kim * School of Chemistry, Seoul National University, Seoul 151-742, Republic@snu.ac.kr (M.S. Kim). www.elsevier.com/locate/cplett Chemical Physics Letters 431 (2006) 19­23 #12

Kim, Myung Soo

373

Nanowire Impact Ionization FETs  

NASA Astrophysics Data System (ADS)

One limiting factor in the scaling of transistor technology is the room temperature limit of 60 mV/decade of the inverse sub-threshold slope. As supply- and threshold voltages are scaled down leakage currents rise exponentially causing the standby power of highly integrated circuits to suffer. New types of devices based on band-to-band tunneling [1] or impact ionization [2] have recently been demonstrated that can circumvent the 60 mV/decade limit thereby offering lower leakage currents. We have demonstrated vertical integration [3] of a single surround-gated silicon nanowire field-effect transistor (NW FET) having an inverse sub-threshold slope as low as 6 mV/decade at room temperature that spans four orders of magnitude in current [4]. The transistor shows slopes below 60 mV/decade for supply voltages above 2 V. Due to the use of a top Schottky contact and two ungated regions the devices show ambipolar characteristics with impact ionization for both electron and hole branch. The rather small voltages reduce hot carrier injection into the gate dielectric making threshold voltage shifts and degradation of the performance minimal. [1] J. Appenzeller, et al., Phys. Rev. Lett. 93, 196805 (2004). [2] K. Gopalakrishnan, et al., IEDM Tech. Dig., 289 (2002). [3] V. Schmidt et al., Small 2, 85 (2006). [4] M. T. Björk et al., Appl. Phys. Lett. 90, 142110 (2007).

Bjork, Mikael

2008-03-01

374

Electron ionization of cyclohexene  

NASA Astrophysics Data System (ADS)

The absolute total cross section of electron ionization on cyclohexene (CHE) and the branching ratios of the product ions are measured in an electron energy range of 10–200 eV. The total cross section reaches a maximum of 1.5 × 10?15 cm2 at 80 eV. Sixteen noteworthy product ions are observed from the ionization of CHE that have partial cross sections greater than 5 × 10?18 cm2 at 50 eV: C2H3+, C3H3,5+, C4H2–7+, C5H5–7+, and C6H5,7,9,10+, where branching ratios are reported for each. The most abundant ions within the electron energy range studied are the parent ion C6H10+ and fragment ions C5H7+ and C4H6+, with combined abundance accounting more than half of the ion population. The reaction pathways forming certain fragment ions at energies near their thresholds are discussed.

Jiao, C. Q.; Adams, S. F.

2014-11-01

375

Positive and negative perfectionism  

Microsoft Academic Search

Previous research into perfectionism has focused on clinical populations resulting in a bias towards a negativistic, pathologically inclined conceptualization. The present study investigated the possibility of distinguishing aspects of perfectionism on the basis of perceived consequences, mirroring a behavioural distinction between positive and negative reinforcement. A 40-item questionnaire, designed to measure perfectionism defined in terms of both positive and negative

L. A. Terry-Short; R. Glynn Owens; P. D. Slade; M. E. Dewey

1995-01-01

376

Positive, Zero, or Negative?  

NSDL National Science Digital Library

This lesson involves students using positive and negative numbers to represent quantities in real-world contexts, explaining the meaning of zero in each situation. Students will understand the positive and negative numbers are used together to describe quantities having opposite values.

Brown, Kathleen

2012-09-16

377

Ontological Metaphors for Negative Energy in an Interdisciplinary Context  

ERIC Educational Resources Information Center

Teaching about energy in interdisciplinary settings that emphasize coherence among physics, chemistry, and biology leads to a more central role for chemical bond energy. We argue that an interdisciplinary approach to chemical energy leads to modeling chemical bonds in terms of negative energy. While recent work on ontological metaphors for energy…

Dreyfus, Benjamin W.; Geller, Benjamin D.; Gouvea, Julia; Sawtelle, Vashti; Turpen, Chandra; Redish, Edward F.

2014-01-01

378

Capillary Atmospheric Pressure Electron Capture Ionization (cAPECI): A Highly Efficient Ionization Method for Nitroaromatic Compounds  

NASA Astrophysics Data System (ADS)

We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2 - or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2 - leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.

Derpmann, Valerie; Mueller, David; Bejan, Iustinian; Sonderfeld, Hannah; Wilberscheid, Sonja; Koppmann, Ralf; Brockmann, Klaus J.; Benter, Thorsten

2014-03-01

379

Capillary atmospheric pressure electron capture ionization (cAPECI): a highly efficient ionization method for nitroaromatic compounds.  

PubMed

We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry. PMID:24399666

Derpmann, Valerie; Mueller, David; Bejan, Iustinian; Sonderfeld, Hannah; Wilberscheid, Sonja; Koppmann, Ralf; Brockmann, Klaus J; Benter, Thorsten

2014-03-01

380

Amplification of critical velocity ionization by associative ionization  

NASA Astrophysics Data System (ADS)

The importance of associative ionization (AI) in barium jet critical ionization velocity (CIV) experiments in space is discussed. It is suggested that AI reactions involving barium may occur in these experiments, and since the products would be indistinguishable from those generated by electron impact ionization, it is likely that the AI-generated ions may be mistaken for those generated by CIV. The electrons formed in AI and by electron impact may be energized by the ion beams, generated by both CIV and AI. The energized electrons may ionize, enhancing the CIV process. In this way, the AI-CIV double process could amplify CIV. The amplification is especially important for sustaining CIV when the CIV energy budget is tight or when the ionization rate due to CIV alone is too low to satisfy Townsend's criterion. An AI-assisted experiment in which a samarium beam could undergo AI, promoting CIV in an accompanying xenon beam, is suggested.

Lai, Shu T.; Murad, Edmond; McNeil, William J.

1992-04-01

381

Ionization photophysics and spectroscopy of cyanoacetylene  

SciTech Connect

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11–15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC{sub 3}N involves new aspects and new assignments of the vibrational components to excitation of the A{sup 2}?{sup +} and B{sup 2}? states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B{sup 2}? state of HC{sub 3}N{sup +}. A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C{sup 2}?{sup +} state of HC{sub 3}N{sup +} at ?17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6–15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C–H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.

Leach, Sydney; Champion, Norbert [LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon (France)] [LERMA UMR CNRS 8112, Observatoire de Paris-Meudon, 5 place Jules-Jansen, 92195 Meudon (France); Garcia, Gustavo A.; Fray, Nicolas; Gaie-Levrel, François [Synchrotron SOLEIL, L’Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex (France)] [Synchrotron SOLEIL, L’Orme des Merisiers, St. Aubin, B.P. 48, 91192, Gif-sur-Yvette Cedex (France); Mahjoub, Ahmed; Bénilan, Yves; Gazeau, Marie-Claire; Schwell, Martin [LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil (France)] [LISA UMR CNRS 7583, Université Paris Est Créteil and Université Paris Diderot, Institut Pierre Simon Laplace, 61 Avenue du Général de Gaulle, 94010 Créteil (France)

2014-05-07

382

Dissociative electron attachment negative ion mass spectrometry: a chlorine-specific detector for gas chromatography  

NASA Astrophysics Data System (ADS)

This work describes the application of negative ion chemical ionization, optimized for dissociative electron attachment (DEA), to location of unknown trace chlorinated compounds in complex gas chromatograms by selected ion recording (SIR) of m / z 35 and 37. The DEA-SIR technique is compared with other GC detectors, including the electron capture detector, electrolytic conductivity detector, the atomic emission detector and the chemical reaction interface mass spectrometry method, with respect to selectivity for chlorine, sensitivity, linear dynamic range, and general robustness and ease of use. When applied to quantitative analysis of target analytes such as polychlorobiphenyls, the DEA-SIR method has potential problems arising from the possibility of suppression effects due to abundant co-eluting components, and possible alleviating measures are discussed. In addition to these practical investigations, literature information on the fundamental physical and chemical phenomena underlying the DEA process is summarized in order to guide future work on extension to other compound types and on general improvements to the technique.

Curtis, Jonathan M.; Boyd, Robert K.

1997-11-01

383

Transmission geometry laser desorption atmospheric pressure photochemical ionization mass spectrometry for analysis of complex organic mixtures.  

PubMed

We present laser desorption atmospheric pressure photochemical ionization mass spectrometry (LD/APPCI MS) for rapid throughput analysis of complex organic mixtures, without the need for matrix, electric discharge, secondary electrospray, or solvents/vaporizers. Analytes dried on a microscope slide are vaporized in transmission geometry by a laser beam aligned with the atmospheric pressure inlet of the mass spectrometer. The laser beam initiates a cascade of reactions in the region between the glass slide and MS inlet, leading to generation of reagent ions for chemical ionization of vaporized analyte. Positive analyte ions are generated predominantly by proton transfer, charge exchange, and hydride abstraction, whereas negative ions are generated by electron capture or proton transfer reactions, enabling simultaneous analysis of saturated, unsaturated, and heteroatom-containing hydrocarbons. The absence of matrix interference renders LD/APPCI MS particularly useful for analysis of small molecules (<2000 Da) such as those present in petroleum crude oil and petroleum deposits. [M + H](+) and M(+•) dominate the positive-ion mass spectra for olefins and polyaromatic hydrocarbons, whereas saturated hydrocarbons are observed mainly as [M - H](+) and/or M(+•). Heteroatom-containing hydrocarbons are observed predominantly as [M + H](+). [M - H](-) and M(-•) are the dominant negative ions observed for analytes of lower gas-phase basicity or higher electron affinity than O2. The source was coupled with a 9.4 T Fourier transform ion cyclotron resonance mass spectrometer (FTICR MS) to resolve and identify thousands of peaks from Athabasca bitumen heavy vacuum gas oil distillates (400-425 and 500-538 °C), enabling simultaneous characterization of their polar and nonpolar composition. We also applied LD/APPCI FTICR MS for rapid analysis of sodium and calcium naphthenate deposits with little to no sample pretreatment to provide mass spectral fingerprints that enable reliable compositional characterization. PMID:25347814

Nyadong, Leonard; Mapolelo, Mmilili M; Hendrickson, Christopher L; Rodgers, Ryan P; Marshall, Alan G

2014-11-18

384

Kriging without negative weights  

SciTech Connect

Under a constant drift, the linear kriging estimator is considered as a weighted average of n available sample values. Kriging weights are determined such that the estimator is unbiased and optimal. To meet these requirements, negative kriging weights are sometimes found. Use of negative weights can produce negative block grades, which makes no practical sense. In some applications, all kriging weights may be required to be nonnegative. In this paper, a derivation of a set of nonlinear equations with the nonnegative constraint is presented. A numerical algorithm also is developed for the solution of the new set of kriging equations.

Szidarovszky, F.; Baafi, E.Y.; Kim, Y.C.

1987-08-01

385

Ionizing radiation detector  

DOEpatents

An ionizing radiation detector is provided which is based on the principle of analog electronic integration of radiation sensor currents in the sub-pico to nano ampere range between fixed voltage switching thresholds with automatic voltage reversal each time the appropriate threshold is reached. The thresholds are provided by a first NAND gate Schmitt trigger which is coupled with a second NAND gate Schmitt trigger operating in an alternate switching state from the first gate to turn either a visible or audible indicating device on and off in response to the gate switching rate which is indicative of the level of radiation being sensed. The detector can be configured as a small, personal radiation dosimeter which is simple to operate and responsive over a dynamic range of at least 0.01 to 1000 R/hr.

Thacker, Louis H. (Knoxville, TN)

1990-01-01

386

Prompt ionization in the CRIT II barium releases  

NASA Astrophysics Data System (ADS)

Observations of electron and ion distributions inside a fast neutral barium jet in the ionosphere show significant fluxes within 4 km of release, presumably related to beam plasma instability processes involved in the Critical Ionization Velocity (CIV) effect. Electron fluxes exceeding 5 x 10 exp 12/sq cm-str-sec-keV were responsible for ionizing both the streaming barium and ambient oxygen. Resulting ion fluxes seem to be consistent with 1-2 percent ionization of the fast barium, as reported by optical observations, although the extended spatial distribution of the optically observed ions is difficult to reconcile with the in situ observations. When the perpendicular velocity of the neutrals falls below critical values, these processes shut off. Although these observations resemble the earlier Porcupine experimental results (Haerendel, 1982), theoretical understanding of the differences between these data and that of earlier negative experiments is still lacking.

Torbert, R. B.; Kletzing, C. A.; Liou, K.; Rau, D.

1992-05-01

387

21 CFR 579.40 - Ionizing radiation for the treatment of poultry feed and poultry feed ingredients.  

Code of Federal Regulations, 2014 CFR

... Ionizing radiation for the treatment of complete poultry diets and poultry feed ingredients may be safely used as follows...is used as a single treatment for rendering complete poultry diets or poultry feed ingredients salmonella negative as...

2014-04-01

388

21 CFR 579.40 - Ionizing radiation for the treatment of poultry feed and poultry feed ingredients.  

Code of Federal Regulations, 2011 CFR

... Ionizing radiation for the treatment of complete poultry diets and poultry feed ingredients may be safely used as follows...is used as a single treatment for rendering complete poultry diets or poultry feed ingredients salmonella negative as...

2011-04-01

389

21 CFR 579.40 - Ionizing radiation for the treatment of poultry feed and poultry feed ingredients.  

Code of Federal Regulations, 2012 CFR

... Ionizing radiation for the treatment of complete poultry diets and poultry feed ingredients may be safely used as follows...is used as a single treatment for rendering complete poultry diets or poultry feed ingredients salmonella negative as...

2012-04-01

390

21 CFR 579.40 - Ionizing radiation for the treatment of poultry feed and poultry feed ingredients.  

Code of Federal Regulations, 2010 CFR

... Ionizing radiation for the treatment of complete poultry diets and poultry feed ingredients may be safely used as follows...is used as a single treatment for rendering complete poultry diets or poultry feed ingredients salmonella negative as...

2010-04-01

391

21 CFR 579.40 - Ionizing radiation for the treatment of poultry feed and poultry feed ingredients.  

Code of Federal Regulations, 2013 CFR

... Ionizing radiation for the treatment of complete poultry diets and poultry feed ingredients may be safely used as follows...is used as a single treatment for rendering complete poultry diets or poultry feed ingredients salmonella negative as...

2013-04-01

392

Electron-Driven Ionization of Processing Gases: Status and Perspectives  

NASA Astrophysics Data System (ADS)

In 1985, experimentally determined absolute partial and total electron-impact ionization cross sections for 31 molecules had been reported in the literature [1]. Today, the number of molecules, for which cross sections have been measured, exceeds 100. Experimental ion formation studies have included work involving free radicals and clusters as targets as well as the study of metastable ionic decay routes. Much effort has been devoted to the study of electron-driven ionization of molecules and free radicals of importance top the plasma processing community. These include many halogen-bearing species, but also molecules such as diborane and silane. While a rigorous, fully quantum mechanical theoretical treatment of molecular ionization processes is still impossible (because of the complexity of the ionization process and the complexity of the targets under study), semi-rigorous approaches such as the method of Khare and co-workers, the Binary Encounter Bethe (BEB) approach of Kim and co-workers, and the Deutsch-M"ark (DM) formalism (see Ref. [2] for details of these theoretical approaches) have made [2] significant progress. This talk will review recent progress in the experimental (and to a lesser extent theoretical) progress in the field of electron-induced ionization of processing gases. Special emphasis will be placed on recent studies of the electron-impact ionization of Cl-bearing molecules and radicals and the respective role direct vs. indirect ionization processes for these targets. This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, US Department of Energy. [1] ``Electron Impact ionization'', T.D. M"ark, G.H. Dunn (editors), Springer Verlag: Vienna (1985) [2] H. Deutsch, K. Becker, S. Matt, and T.D. M"ark, Int. J. Mass Spectrom. 197, 37 (2000)

Becker, Kurt

2007-10-01

393

Gram-negative bacteremia  

Microsoft Academic Search

In the 1960s, almost all patients who developed gram-negative bacteremia during granulocytopenia died; death occurred before blood culture results were available in about 50% of cases; many patients received antibiotics that were, at best, suboptimal and frequently inactive against the invading pathogen. In the early 1970s epidemiological studies demonstrated that more than 50% of gram-negative bacteremias were caused by hospital-acquired

Stephen C. Schimpff

1993-01-01

394

No to negative data  

SciTech Connect

A frequent criticism in biology is that we don’t publish our negative data. As a result, the literature has become biased towards papers that favor specific hypotheses1. Some scientists have become so concerned about this trend that they have created journals dedicated to publishing negative results (e.g. the Journal of Negative Results in Biomedicine). Personally, I don’t think they should bother. I say this because I believe negative results are not worth publishing. Rest assured that I do not include drug studies that show a lack of effectiveness towards a specific disease or condition. This type of finding is significant in a societal context, not a scientific one, and thus we all have a vested interest in seeing this type of result published. I am talking about a set of experimental results that fail to support a particular hypothesis. The problem with these types of negative results is that they don’t actually advance science. Science is a set of ideas that can be supported by observations. A negative result does not support any specific idea, but only tells you what isn’t right. Well, there are only a small number of potential hypotheses that are correct, but essentially an infinite number of ideas are not correct. I don’t want to waste my time reading a paper about what doesn’t happen, just about those things that do. I can remember a positive result because I can associate it with a specific concept. What do I do with a negative one? It is hard enough to following the current literature. A flood of negative results would make that task all but impossible

Wiley, H. S.

2008-04-01

395

Isotropic Single Negative Metamaterials  

Microsoft Academic Search

This paper presents the application of simple, and therefore cheap, planar resonators for building 3D isotropic metamaterials. These resonators are: a broad- side-coupled split ring resonator with a magnetic response providing negative permeability; an electric dipole termi- nated by a loop inductor together with a double H-shaped resonator with an electric response providing negative permittivity. Two kinds of 3D isotropic

Pavel PROTIVA; Michal BLÁHA; Ján ZEHENTNER

396

Characterization of vegetable oils: detailed compositional fingerprints derived from electrospray ionization fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

Adulteration of vegetable oil is of concern for both commercial and health reasons. Compositional based fingerprints can potentially reveal both the oil source and its possible adulteration. Here, electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) resolves and identifies literally thousands of distinct chemical components of commercial canola, olive, and soybean oils, without extraction or other wet chemical separation pretreatment. In negative-ion ESI FT-ICR MS, the acidic components of soybean oil are easily distinguished from those of canola and olive oil based on relative abundances of C(18) fatty acids, whereas olive oil differs from canola and soybean oil based on relative abundances of tocopherols. In positive-ion ESI FT-ICR MS, the three oils are readily distinguished according to the relative abundances of di- and triacylglycerols with various numbers of double bonds in the fatty acid chains. We demonstrate the detection of soybean oil as an adulterant of olive oil, based on relative abundances of members of each of several chemical families. We suggest that the detailed chemical compositions of vegetable oils can be used to characterize them and to detect and identify adulterants. PMID:15315364

Wu, Zhigang; Rodgers, Ryan P; Marshall, Alan G

2004-08-25

397

Approaches for protection standards for ionizing radiation and combustion pollutants.  

PubMed Central

The question "can the approach used for radiation protection standards, i.e., to extrapolate dose--response relationships to low doses, be applied to combustion pollutants?" provided a basis for discussion. The linear, nonthreshold model postulated by ICRP and UNSCEAR for late effects of ionizing radiation is described and discussed. The utility and problems of applying this model to the effects of air pollutants constitute the focus of this paper. The conclusion is that, in the absence of evidence to the contrary, one should assume the same type of dose--effect relation for chemical air pollutants as for ionizing radiation. PMID:648475

Butler, G C

1978-01-01

398

Higher-Sensitivity Ionization Trace-Species Detector  

NASA Technical Reports Server (NTRS)

Electron source and electron optics of reversal electron-attachment detector modified to increase sensitivity. Original version described in "High-Sensitivity Ionization Trace-Species Detector" (NPO-17596). Used to detect molecules of particular chemical species of interest (e.g., narcotics, explosives, or organic wastes) present in air at low concentrations, and known to attach extremely low-energy electrons. Apparatus does this by ionizing molecules from sampled atmosphere, then detecting ions of species of interest. Detector features indirectly heated spherical cathode and redesigned electron optics, together, deliver more electrons at low kinetic energy to reversal plane, R. Greater electron current generates more ions for detection.

Boumsellek, Said; Chutjian, Ara

1995-01-01

399

Rapid and simultaneous determination of sulfonate ester genotoxic impurities in drug substance by liquid chromatography coupled to tandem mass spectrometry: comparison of different ionization modes.  

PubMed

Two ionization techniques for liquid chromatography-mass spectrometry (LC-MS) determination of sulfonate ester potentially genotoxic impurities (PGIs) were evaluated. Twelve PGIs including methyl, ethyl, propyl and isopropyl esters of methanesulfonate, benzenesulfonate and p-toluenesulfonate were studied in this research. Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources were compared in terms of performance and quality parameters for detection of the twelve PGIs. Their mass spectra obtained by APCI and ESI were very different in both fragment ions and relative abundances. In APCI negative ion mode the twelve sulfonate esters showed their stable precursor ions of [M-alkyl](-), which readily yielded product ions of [M-alkyl-CH3](-) (for aliphatic sulfonate esters) or [M-alkyl-SO2](-) (for aromatic sulfonate esters) with collision-induced dissociation (CID) applied; and working in selected reaction monitoring (SRM) mode has allowed limits of detection to be decreased. In the case of ESI ionization, these compounds showed their precursor ions [M+H](+), but their abundance was easily competed by formation of ions [M+NH4](+) and/or [M+Na](+), which led to poor analytical sensitivity and reproducibility. Although mobile phase additives could enhance the responses of adduct ions like [M+NH4](+) and [M+Na](+), no improvement was obtained when using SRM mode. Twelve sulfonate esters were systematically compared and APCI was shown to be a better ionization technique for rapid and sensitive determination of these PGIs. Performance of the developed approach for rapid determination of 12 PGIs was also evaluated. Quality parameters were established and good precision (relative standard deviations <8%) and very low limits (2-4ng/mL) of detection were obtained, mainly when using APCI in SRM mode. PMID:24997109

Guo, Tian; Shi, Yuanyuan; Zheng, Li; Feng, Feng; Zheng, Feng; Liu, Wenyuan

2014-08-15

400

Negative refraction without negative index in metallic photonic crystals  

E-print Network

Negative refraction without negative index in metallic photonic crystals Chiyan Luo, Steven G: It is shown that certain metallic photonic crystals can enable negative refraction and subwavelength imaging negative values of and µ," Sov. Phys. Usp. 10, 509-514 (1968). 5. J. B. Pendry, "Negative refraction makes

401

Ionizing gas breakdown waves in strong electric fields.  

NASA Technical Reports Server (NTRS)

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

402

High pressure xenon ionization detector  

DOEpatents

A method is provided for detecting ionization comprising allowing particles that cause ionization to contact high pressure xenon maintained at or near its critical point and measuring the amount of ionization. An apparatus is provided for detecting ionization, the apparatus comprising a vessel containing a ionizable medium, the vessel having an inlet to allow high pressure ionizable medium to enter the vessel, a means to permit particles that cause ionization of the medium to enter the vessel, an anode, a cathode, a grid and a plurality of annular field shaping rings, the field shaping rings being electrically isolated from one another, the anode, cathode, grid and field shaping rings being electrically isolated from one another in order to form an electric field between the cathode and the anode, the electric field originating at the anode and terminating at the cathode, the grid being disposed between the cathode and the anode, the field shaping rings being disposed between the cathode and the grid, the improvement comprising the medium being xenon and the vessel being maintained at a pressure of 50 to 70 atmospheres and a temperature of 0.degree. to 30.degree. C.

Markey, John K. (New Haven, CT)

1989-01-01

403

High pressure xenon ionization detector  

DOEpatents

A method is provided for detecting ionization comprising allowing particles that cause ionization to contact high pressure xenon maintained at or near its critical point and measuring the amount of ionization. An apparatus is provided for detecting ionization, the apparatus comprising a vessel containing a ionizable medium, the vessel having an inlet to allow high pressure ionizable medium to enter the vessel, a means to permit particles that cause ionization of the medium to enter the vessel, an anode, a cathode, a grid and a plurality of annular field shaping rings, the field shaping rings being electrically isolated from one another, the anode, cathode, grid and field shaping rings being electrically isolated from one another in order to form an electric field between the cathode and the anode, the electric field originating at the anode and terminating at the cathode, the grid being disposed between the cathode and the anode, the field shaping rings being disposed between the cathode and the grid, the improvement comprising the medium being xenon and the vessel being maintained at a pressure of 50 to 70 atmospheres and a temperature of 0 to 30 C. 2 figs.

Markey, J.K.

1989-11-14

404