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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

PULSED POSITIVE ION NEGATIVE ION CHEMICAL IONIZATION MASS SPECTROMETRIC APPLICATONS TO ENVIRONMENTAL AND HAZARDOUS WASTE ANALYSIS  

EPA Science Inventory

The simultaneous acquisition of both positive ion and negative ion data under chemical ionization mass spectrometric conditions can aid in the confirmation of assignments made by electron impact gas chromatography mass spectrometry or electron capture gas chromatography. Pulsed p...

3

ELECTRON AFFINITIES OF POLYNUCLEAR AROMATIC HYDROCARBONS AND NEGATIVE ION CHEMICAL IONIZATION SENSITIVITIES  

EPA Science Inventory

Negative-ion chemical-ionization mass spectrometry (NICI MS) has the potential to be a very useful technique in identifying various polycyclic aromatic hydrocarbons (PAHs) in soil and sediment samples. Some PAHs give much stronger signals under NICI MS conditions than others. On ...

4

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 ...

5

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 ...

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

Regioisomers of octanoic acid-containing structured triacylglycerols analyzed by tandem mass spectrometry using ammonia negative ion chemical ionization  

Microsoft Academic Search

Tandem mass spectrometry based on ammonia negative ion chemical ionization and sample introduction via direct exposure probe was applied to analysis of regioisomeric structures of octanoic acid containing structured triacylglycerols\\u000a (TAG) of type MML, MLM, MLL, and LML (M, medium-chain fatty acid; L, long-chain fatty acid). Collision-induced dissociation\\u000a of deprotonated parent TAG with argon was used to produce daughter ion

J.-P. Kurvinen; H. Mu; H. Kallio; X. Xu; C. E. Høy

2001-01-01

8

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...

9

Differentiation of Aroclors using linear discrimination for environmental samples analyzed by electron capture negative ion chemical ionization mass spectrometry  

SciTech Connect

Environmental samples suspected of containing polychlorinated biphenyls (PCBs) and analyzed by Environmental Protection Agency (EPA) methods frequently contain non-PCB components, such as phinalates, polyaromatic hydrocarbons, or organochlorine pesticides. The presence of these interferences can often obscure the gas chromatographic (GC) patterns and cause problems in differentiating the aroclor types by visual inspection. Because EPA methods require the identification of Aroclor types in order to determine which Aroclor standard should be used for the quantitation calibration, and possibly, to trace the source of PCB occurrences, electron capture negative ion chemical ionization (ECNICI) mass spectrometry was used to provide additional parameters for discriminating PCB congeners from the interferences. In this study, eight Aroclors (i.e., 1016, 1232, 1242, 1248, 1254, 1260, 1262, and 1268) were analyzed by ECNICI for a range of concentration levels. Using selective ion display, the ion abundances of the prominent peaks in the isotopic clusters of molecular ions were measured for eight PCB homologs (Cl) within their GC retention time windows for each sample. Corresponding relative ion abundances from eight Aroclor standards were used as classification training sets. These training sets were used to develop a classification algorithm using standard linear discriminant analysis to classify the PCBs present in an unknown sample(s) as a specific Aroclor. This technique employed a sequential application of two sets of linear discriminant functions to successfully identify known EPA quality control and environmental samples. However, classifications of Aroclor mixtures were less successful. 26 refs., 4 figs., 4 tabs.

Ma, C.Y.; Bayne, C.K. (Oak Ridge National Lab., TN (United States))

1993-03-15

10

[Determination of four insecticide residues in honey and royal jelly by gas chromatography-negative chemical ionization mass spectrometry].  

PubMed

A method was developed for the determination of four insecticide residues in honey and royal jelly by gas chromatography-negative chemical ionization mass spectrometry (GC-NCI/MS). The honey and royal jelly samples were treated with different preparation methods as the result of the different components. The honey sample was extracted with ethyl acetate and cleaned up with primary second amine, and the royal jelly sample was extracted with acetonitrile-water (1:1, v/v), and cleaned up with a C18 solid-phase extraction column. Finally, the extracts of the honey and royal jelly were analyzed by GC-NCI/MS in selected ion monitoring (SIM) mode separately. External standard calibration method was used for quantification. The linearities of calibration curves of the four insecticides were good with the correlation coefficients greater than 0.99 in the range of 50-500 microg/L. The limits of the detection (LODs) of the four insecticides were in the range of 0.12- 5.0 microg/kg, and the limits of the quantification (LOQs) were in the range of 0.40-16.5 microg/kg. The recoveries of the four insecticides spiked in honey and royal jelly at three spiked levels (10, 15 and 20 microg/kg) were in the range of 78.2 -110.0%, and the relative standard deviations (RSDs) were all below 14%. The sensitivity and selectivity of this method were good with no interfering peaks. The proposed method is simple quick and effective to analyze the four insecticide residues in honey and royal jelly. PMID:25255567

Xia, Guanghui; Shen, Weijian; Yu, Keyao; Wu, Bin; Zhang, Rui; Shen, Chongyu; Zhao, Zengyun; Bian, Xiaohong; Xu, Jiyang

2014-07-01

11

Identification of acylated xanthone glycosides by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry in positive and negative modes from the lichen Umbilicaria proboscidea.  

PubMed

The xanthoside composition of the crude extract of Umbilicaria proboscidea (L.) Schrader was characterized using LC-UV diode array detection and LC-atmospheric pressure chemical ionization (APCI) MS methods. The presence of acylated xanthone-O-glucosides was determined by both positive and negative ion LC-APCI-MS methods. Based on UV and MS spectral data and NMR spectroscopy, a total of 14 compounds (6-O-acylated umbilicaxanthosides A and B) were identified in U. proboscidea for the first time. In order to further develop the applicability of LC-MS techniques in phytochemical characterization, the effect of different ionization energy on fragmentation was studied using APCI. The optimal ionization conditions were achieved in positive ion APCI by using ammonium acetate buffer and in negative ion APCI by using formic acid (pH 4). PMID:12800927

Rezanka, Tomás; Dembitsky, Valery M

2003-05-01

12

Quantification of low levels of organochlorine pesticides using small volumes (?100 ?l) of plasma of wild birds through gas chromatography negative chemical ionization mass spectrometry  

Microsoft Academic Search

A solid phase extraction and gas chromatography with negative chemical ionization mass spectrometry in scan mode (GC-NCI-MS) method was developed to identify and quantify for the first time low levels of organochlorine pesticides (OCs) in plasma samples of less than 100?l from wild birds. The method detection limits ranged from 0.012 to 0.102pg\\/?l and the method reporting limit from 0.036

Laura B. Rivera-Rodríguez; Ricardo Rodríguez-Estrella; James Jackson Ellington; John J. Evans

2007-01-01

13

Identification of acylated xanthone glycosides by liquid chromatography–atmospheric pressure chemical ionization mass spectrometry in positive and negative modes from the lichen Umbilicaria proboscidea  

Microsoft Academic Search

The xanthoside composition of the crude extract of Umbilicaria proboscidea (L.) Schrader was characterized using LC–UV diode array detection and LC–atmospheric pressure chemical ionization (APCI) MS methods. The presence of acylated xanthone-O-glucosides was determined by both positive and negative ion LC–APCI-MS methods. Based on UV and MS spectral data and NMR spectroscopy, a total of 14 compounds (6-O-acylated umbilicaxanthosides A

Tomᚠ?ezanka; Valery M. Dembitsky

2003-01-01

14

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

15

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

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

Osmium isotope ratio determinations by negative thermal ionization mass spectrometry  

Microsoft Academic Search

A new technique for osmium isotope ratio determinations by negative thermal ionization mass spectrometry using the formation of OsO-3 ions is presented. Different filament materials and chemicals to reduce the electron work function are investigated. With Ba(OH)2 and platinum as filament material an ionization efficiency of more than 1% is obtained for nanogram sample amounts. The isotopic abundances of a

Joachim Völkening; Thomas Walczyk; Klaus G. Heumann

1991-01-01

18

Negative electrospray ionization via deprotonation: predicting the ionization efficiency.  

PubMed

Electrospray ionization (ESI) in the negative ion mode has received less attention in fundamental studies than the positive ion electrospray ionization. In this paper, we study the efficiency of negative ion formation in the ESI source via deprotonation of substituted phenols and benzoic acids and explore correlations of the obtained ionization efficiency values (logIE) with different molecular properties. It is observed that stronger acids (i.e., fully deprotonated in the droplets) yielding anions with highly delocalized charge [quantified by the weighted average positive sigma (WAPS) parameter rooted in the COSMO theory] have higher ionization efficiency and give higher signals in the negative-ion ESI/MS. A linear model was obtained, which equally well describes the logIE of both phenols and benzoic acids (R(2) = 0.83, S = 0.40 log units) and contains only an ionization degree in solution (?) and WAPS as molecular parameters. Both parameters can easily be calculated with the COSMO-RS method. The model was successfully validated using a test set of acids belonging neither to phenols nor to benzoic acids, thereby demonstrating its broad applicability and the universality of the above-described relationships between IE and molecular properties. PMID:24731109

Kruve, Anneli; Kaupmees, Karl; Liigand, Jaanus; Leito, Ivo

2014-05-20

19

Quantification of low levels of organochlorine pesticides using small volumes (negative chemical ionization mass spectrometry.  

PubMed

A solid phase extraction and gas chromatography with negative chemical ionization mass spectrometry in scan mode (GC-NCI-MS) method was developed to identify and quantify for the first time low levels of organochlorine pesticides (OCs) in plasma samples of less than 100 microl from wild birds. The method detection limits ranged from 0.012 to 0.102 pg/microl and the method reporting limit from 0.036 to 0.307 pg/microl for alpha, gamma, beta and delta-hexachlorocyclohexane (HCH), heptachlor, aldrin, heptachlor epoxide, endosulfan I, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), dieldrin, endrin, endosulfan-II, endrin-aldehyde and endosulfan-sulfate. Pesticide levels in small serum samples from individual Falco sparverius, Sturnella neglecta, Mimus polyglottos and Columbina passerina were quantified. Concentrations ranged from not detected (n/d) to 204.9 pg/microl for some OC pesticides. All levels in the food web in and around cultivated areas showed the presence of pesticides notwithstanding the small areas for agriculture existing in the desert of Baja California peninsula. PMID:17240024

Rivera-Rodríguez, Laura B; Rodríguez-Estrella, Ricardo; Ellington, James Jackson; Evans, John J

2007-07-01

20

Detection and quantification of 1,N6-ethenoadenine in human urine by stable isotope dilution capillary gas chromatography/negative ion chemical ionization/mass spectrometry.  

PubMed

1,N(6)-Ethenoadenine (epsilonAde) is a promutagenic lesion detected in tissue DNA; it has been shown that epsilonAde can be repaired by human DNA glycosylases, and it is expected to be excreted in urine. In this paper, we present for the first time detection and accurate quantification of epsilonAde in human urine samples by a highly sensitive and specific stable isotope dilution gas chromatography/negative ion chemical ionization/mass spectrometric assay (GC/NICI/MS). Analysis by GC/NICI/MS includes adduct enrichment by a solid phase extraction column, followed by electrophore labeling and postderivatization cleanup. Using selective ion monitoring mode, the assay allows quantification of 0.5 pg of epsilonAde in as little as 0.1 mL of the urine sample, which is equivalent to corresponding concentration quantification limit of 31 pM. Using this assay, concentrations of epsilonAde in the 24 h urine samples of 23 healthy individuals were determined, which ranged from 0 to 124 pg/mL. After we adjusted for creatinine, a statistically significant correlation was found between epsilonAde excretion and cigarette smoking in males (p = 0.03). Thus, this stable isotope dilution GC/NICI/MS assay offers a sensitive and accurate quantification of urinary epsilonAde as a potential biomarker for oxidative damage of DNA and repair. PMID:12971797

Chen, Hauh-Jyun Candy; Chiu, Wei-Loong

2003-09-01

21

Mixed-mode SPE for a multi-residue analysis of benzodiazepines in whole blood using rapid GC with negative-ion chemical ionization MS.  

PubMed

A sensitive and selective method for simultaneous quantitation of 15 benzodiazepines in human whole blood using rapid GC with negative-ion chemical ionization MS is proposed. A mixed-mode cation-exchange polymeric sorbent was used for SPE. Different extraction solvents or mixtures of solvents of different compositions for elution of the adsorbed analytes, and washing steps for eliminating interferences in the column were tested. Analytes were eluted from the column using 5% v/v NH4 OH in methanol. A derivatization step using different silylation reagents, time, and temperature was tested. Extracts from SPE were silylated by a mixture of N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide, acetonitrile, ethyl acetate, and subjected to gas chromatographic analysis. The LODs of 15 benzodiazepines in whole blood samples ranged from 0.24-0.62 ng mL(-1). The RSDs of samples used for three different quality control concentration levels were lower than 7.0%, and the accuracy ranged from 89.5 to 110.5%. The results show that the developed method is accurate, sensitive, selective, and very fast. Finally, the applicability of this method for determination of trace concentrations of several benzodiazepines in real blood samples has been demonstrated. PMID:23505213

Karlonas, Nerijus; Padarauskas, Audrius; Ramanavicius, Arunas; Ramanaviciene, Almira

2013-04-01

22

Development and validation of a gas chromatography–negative chemical ionization tandem mass spectrometry method for the determination of ethyl glucuronide in hair and its application to forensic toxicology  

Microsoft Academic Search

Ethyl glucuronide (EtG) is a minor and direct metabolite of ethanol. EtG is incorporated into the growing hair allowing retrospective investigation of chronic alcohol abuse. In this study, we report the development and the validation of a method using gas chromatography–negative chemical ionization tandem mass spectrometry (GC–NCI-MS\\/MS) for the quantification of EtG in hair. EtG was extracted from about 30mg

Hicham Kharbouche; Frank Sporkert; Stéphanie Troxler; Marc Augsburger; Patrice Mangin; Christian Staub

2009-01-01

23

Determination of phenolic endocrine disrupting chemicals and acidic pharmaceuticals in surface water of the Pearl Rivers in South China by gas chromatography-negative chemical ionization-mass spectrometry.  

PubMed

An analytical method for phenolic endocrine disrupting chemicals and acidic pharmaceuticals in river water was developed using gas chromatography mass spectrometry (GC-MS) coupled with negative chemical ionization (NCI) technique, and used for the determination of these compounds in the Pearl Rivers (Liuxi, Zhujiang and Shijing Rivers). Derivatization using pentafluorobenzoyl chloride (PFBOCl) and pentafluorobenzyl bromide (PFBBr) before GC-MS analysis were applied and optimized for phenolic compounds and acidic compounds, respectively. The target compounds were analyzed for river waters from the upstream to downstream of the Pearl Rivers. Phenolic compounds 4-tert-octylphenol (4-t-OP), 4-nonylphenol (4-NP), bisphenol-A (BPA), estrone (E1), estradiol (E2) and triclosan (TCS) were detected at trace or low levels in the water samples from Liuxi River and Zhujiang River. Diethylstilbestrol (DES) was not detected in the Pearl Rivers. The highest concentrations of the phenolic compounds were found in Shijing River, and they were 3150 ng/L for 4-t-OP, 11,300 ng/L for 4-NP, 1040 ng/L for BPA, 79 ng/L for E1, 7.7 ng/L for E2 and 355 ng/L for TCS, respectively. Only a few acidic pharmaceuticals were detected at low concentrations in water from Liuxi River and Zhujiang River, but the highest concentrations for the acidic pharmaceuticals were also found in Shijing River. The highest concentrations detected for clofibric acid, ibuprofen, gemfibrozil, naproxen, mefenamic acid and diclofenac were 17 ng/L, 685 ng/L, 19.8 ng/L, 125 ng/L, 24.6 ng/l and 150 ng/L, respectively. The results suggest Liuxi and Zhujiang Rivers are only slightly contaminated and can be used as drinking water sources, but Shijing River is heavily polluted by the wastewater from nearby towns. PMID:19004474

Zhao, Jian-Liang; Ying, Guang-Guo; Wang, Li; Yang, Ji-Feng; Yang, Xiao-Bing; Yang, Li-Hua; Li, Xu

2009-01-01

24

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

25

New Automated and High-Throughput Quantitative Analysis of Urinary Ketones by Multifiber Exchange-Solid Phase Microextraction Coupled to Fast Gas Chromatography/Negative Chemical-Electron Ionization/Mass Spectrometry  

PubMed Central

The present research is focused on automation, miniaturization, and system interaction with high throughput for multiple and specific Direct Immersion-Solid Phase Microextraction/Fast Gas Chromatography analysis of the urinary ketones. The specific Mass Spectrometry instrumentation, capable of supporting such the automated changeover from Negative Chemical to Electron Ionization mode, as well as the automation of the preparation procedure by new device called MultiFiber Exchange, through change of the fibers, allowed a friendly use of mass spectrometry apparatus with a number of advantages including reduced analyst time and greater reproducibility (2.01–5.32%). The detection limits for the seven ketones were less than 0.004?mg/L. For an innovative powerful meaning in high-throughput routine, the generality of the structurally informative Mass Spectrometry fragmentation patterns together with the chromatographic separation and software automation are also investigated. PMID:20628512

Pacenti, Marco; Dugheri, Stefano; Traldi, Pietro; Degli Esposti, Filippo; Perchiazzi, Nicola; Franchi, Elena; Calamante, Massimo; Kikic, Ireneo; Alessi, Paolo; Bonacchi, Alice; Salvadori, Edoardo; Arcangeli, Giulio; Cupelli, Vincenzo

2010-01-01

26

Development of Ion Drift-Chemical Ionization Mass Spectrometry  

E-print Network

as their oxidation products can be quantified simultaneously by PTR-MS. Some desirable features offered by PTR are chemically ionized into positive or negative product ions with a well- controlled ion-molecule reaction time to yield a product ion, which is analyzed by a quadrupole mass analyzer for species identification

27

Use of Negative Air Ionization for Reducing Bacterial Pathogens and Spores on Stainless Steel Surfaces  

Microsoft Academic Search

SUMMARY The use of chemicals in food plant sanitation for removing and killing microorganisms could be reduced by the use of alternative nonchemical interventions. Supercharged negative air ionizers have shown potential to effectively reduce airborne and surface microorganisms. In our earlier studies, a small chamber, controlled at 85% relative humidity and supercharged with a ?25 kV electrostatic space charge system

J. W. Arnold; D. H. Boothe; B. W. Mitchell

2004-01-01

28

CHEMICAL PROTECTION AGAINST IONIZING RADIATION  

Microsoft Academic Search

Recent work on chemical protection against radiation effects in mammals ; is reviewed, especially with respect to whole-body exposure to external radiation. ; This survey shows that many explanations are being offered to account for the ; action of radioprotective agents. In general, the proposed mechanisms are ; concerned with inactivation of radicals and other chemical intermediates, ; depletion of

R. L. Straube; H. M. Patt

1963-01-01

29

Characteristic negative response of the helium ionization detector  

Microsoft Academic Search

When ultrapure helium is used as a carrier gas, the helium ionization detector provides a characteristic response, either positive or negative to each gas. The detector response can be made positive for all gases except neon by the inclusion of a few ppM of gaseous additives to the helium carrier gas, but the inclusion of gaseous additives decreases the detector

Fikry F. Andrawes; Everett K. Gibson

1980-01-01

30

A new concept positive (negative) surface ionization source equipped with a high porosity ionizer  

NASA Astrophysics Data System (ADS)

A versatile, new concept, spherical-geometry, positive (negative) surface-ionization source has been designed, fabricated, and initial 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 ?=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 + conservatively estimated to exceed 60% and as high as ˜50% for F - generation. However, the overall ionization efficiency for F - formation and extraction is ˜1% due to the low efficiency for thermal dissociation of the carrier molecules (assumed to be CsF and AlF). The design features, operational principles, and initial performance of the source for generating Cs + and F -, when operated with Cs, are discussed in this article.

Alton, G. D.; Welton, R. F.; Cui, B.; Murray, S. N.; Mills, G. D.

1998-08-01

31

Thermal and chemical ionization in flames  

Microsoft Academic Search

Conclusions We have determined the rate constants of the potassium ionization process A?A++e? in the flames of 2H2+O2+X (Ar, He) mixtures on the temperature interval 1500–2500° K. The activation energy of this process is close to the ionization potential of potassium (100 kcal).

E. S. Semenov; A. S. Sokolik

1970-01-01

32

Matrix-assisted laser desorption/ionization matrices for negative mode metabolomics.  

PubMed

Matrix-assisted laser desorption/ionization (MALDI) has been shown to be highly sensitive for analyzing low-mass compounds such as metabolites if the right matrix is used. 9-aminoacridine (9AA) is the most commonly employed matrix for negative mode MALDI-MS in metabolomics. However, matrix interferences and the strongly varying sensitivity for different metabolites make a search for alternative matrices desirable, in order to identify compounds with a different chemical background and/or favoring a different range of analytes. We tested the performance of a series of potential negative mode MALDI matrices with a mix of 29 metabolites containing amino acids, nucleotide phosphates and Krebs cycle intermediates. While ethacridine lactate was found to provide limits of detection (LODs) in the low femtomole range for nucleotide phosphates, amino acids and Krebs cycle intermediates in the low picomole range, 4-amino-2-methylquinoline showed LODs in the picomole range for most metabolites, but is capable of ionizing a broader range of analytes than both 9AA and ethacridine. PMID:23841224

Fagerer, Stephan R; Nielsen, Simone; Ibáñez, Alfredo; Zenobi, Renato

2013-01-01

33

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

34

Mass spectral behavior of the hydrolysis products of sesqui- and oxy-mustard type chemical warfare agents in atmospheric pressure chemical ionization  

Microsoft Academic Search

Bis(2-hydroxyethylthio)alkanes and bis(2-hydroxyethylthioalkyl)ethers are important biological and environmental degradation\\u000a products of sulfur mustard analogs known as sesqui- and oxy-mustards. We used atmospheric pressure chemical ionization mass\\u000a spectrometry (APCI MS) to acquire characteristic spectra of these compounds in positive and negative ionization modes. Positive\\u000a APCI mass spectra exhibited [M + H]+; negative APCI MS generated [M + O2]?, [M ? H]?,

Sharon W. Lemire; Doris H. Ash; Rudolph C. Johnson; John R. Barr

2007-01-01

35

Determination of low specific activity iodine-129 off-gas concentrations by GC separation and negative ionization mass spectrometry  

SciTech Connect

This document is the final report of the laboratory development of a method for determining the specific activity of the /sup 129/I emitted from a nuclear fuel reprocessing plant. The technique includes cryogenic sample collection, chemical form separation, quantitation by gas chromatography, and specific activity measurement of each chemical species by negative ionization mass spectrometry. The major conclusions were that both organic and elemental iodine can be quantitatively collected without fractionation and that specific activity measurements as low as one atom of /sup 129/I per 10/sup 5/ atoms of /sup 127/I are possible.

Fernandez, S.J.; Rankin, R.A.; McManus, G.J.; Nielsen, R.A.; Delmore, J.E.; Hohorst, F.A.; Murphy, L.P.

1983-09-01

36

The analysis of trichothecenes in wheat and human plasma samples by chemical ionization tandem mass spectrometry  

Microsoft Academic Search

Ammonia desorption chemical ionization (D\\/CI) tandem mass spectrometry (method A), isobutane D\\/CI tandem mass spectrometry using reactive collisions with ammonia (method B), and gas chromatography negative CI (GC-NCI) tandem mass spectrometry (method C) were compared for the detection and quantitation of trichothecenes in spiked human plasma and wheat samples. The trichothecenes were analyzed as their heptafluorobutyrate (HFB) esters in method

R. Kostiainen; A. Rizzo; A. Hesso

1989-01-01

37

Ambient diode laser desorption dielectric barrier discharge ionization mass spectrometry of nonvolatile chemicals.  

PubMed

In this work, the combined use of desorption by a continuous wave near-infrared diode laser and ionization by a dielectric barrier discharge-based probe (laser desorption dielectric barrier discharge ionization mass spectrometry (LD-DBDI-MS)) is presented as an ambient ionization method for the mass spectrometric detection of nonvolatile chemicals on surfaces. A separation of desorption and ionization processes could be verified. The use of the diode laser is motivated by its low cost, ease of use, and small size. To achieve an efficient desorption, the glass substrates are coated at the back side with a black point (target point, where the sample is deposited) in order to absorb the energy offered by the diode laser radiation. Subsequent ionization is accomplished by a helium plasmajet generated in the dielectric barrier discharge source. Examples on the application of this approach are shown in both positive and negative ionization modes. A wide variety of multiclass species with low vapor pressure were tested including pesticides, pharmaceuticals and explosives (reserpine, roxithromycin, propazine, prochloraz, spinosad, ampicillin, dicloxacillin, enrofloxacin, tetracycline, oxytetracycline, erythromycin, spinosad, cyclo-1,3,5,7-tetramethylene tetranitrate (HMX), and cyclo-1,3,5-trimethylene trinitramine (RDX)). A comparative evaluation revealed that the use of the laser is advantageous, compared to just heating the substrate surface. PMID:23419061

Gilbert-López, Bienvenida; Schilling, Michael; Ahlmann, Norman; Michels, Antje; Hayen, Heiko; Molina-Díaz, Antonio; García-Reyes, Juan F; Franzke, Joachim

2013-03-19

38

Rapid differentiation of refined fuels using negative electrospray ionization/mass spectrometry  

USGS Publications Warehouse

Negative electrospray ionization/MS enabled rapid, specific, and selective screening for unique polar components at parts per million concentrations in commercial hydrocarbon products without extensive sample preparation, separation, chromatography, or quantitation. Commercial fuel types were analyzed with this method, including kerosene, jet fuel, white gas, charcoal lighter fluid, on-road and off-road diesel fuels, and various grades and brands of gasolines. The different types of fuels produced unique and relatively simple spectra. These analyses were then applied to hydrocarbon samples from a large, long-term fuel spill. Although the alkane, isoprenoid, and alkylcyclohexane portions began to biodegrade or weather, the polar components in these samples remained relatively unchanged. The type of fuel involved was readily identified by negative electrospray ionization/MS. This is an abstract of a paper presented at the 230th ACS National Meeting (Washington, DC 8/28/2005-9/1/2005).

Rostad, C. E.; Hostettler, F. D.

2005-01-01

39

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

40

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

41

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

42

Rapid differentiation of refined fuels using negative electrospray ionization/mass spectrometry  

USGS Publications Warehouse

An application of electrospray ionization/mass spectrometry for identification of various commercially refined fuels using the unique signature of polar components, was investigated. The samples were analyzed by mass spectrometry using negative electrospray on an Agilent Series 1100 liquid chromatograph/mass spectrometer. These analysis were applied to hydrocarbon samples from a large, long-term fuel spill which were taken from the subsurface and different extent of biodegradation or weathering. The technique provided rapid identification of hydrocarbons released into the environment because these polar compounds are unique in different fuels.

Rostad, C. E.; Hostettler, F. D.

2005-01-01

43

Solid state chemical ionization for characterization of organic compounds by laser mass spectrometry.  

PubMed

A new technique involving the addition of a compound to the analyte to serve as a source of "reagent" ions has been developed for negative-ion laser mass spectrometry. This "solid state chemical ionization" leads to ions characteristic of the analyte, owing to ion-molecule reactions between the "reagent" ion and the neutral analyte in the laser-generated plume. Polycyclic aromatic hydrocarbons show formation of an ion corresponding to (M + O - H)(-) in their negative-ion laser mass spectra when mixed with compounds such as sym-trinitrobenzene, sodium nitrate and sodium peroxide. NO(-)(2), O(-), and O(-)(2) serve as "reagent" ions in these compounds. Formation of (M + Cl)(-) is seen in the laser mass spectra of glycosides mixed with hexachlorobenzene. Chloride serves as the "reagent" ion in this case. PMID:18964680

Balasanmugam, K; Viswanadham, S K; Hercules, D M

1989-01-01

44

Negative ionization micro electrospray mass spectrometry of oligonucleotides and their complexes.  

PubMed

The utility of negative ionization micro electrospray (microspray) mass spectrometry is demonstrated for detection of oligonucleotides and their non-covalent complexes. A simple microspray ionization source is fabricated from an outer stainless-steel needle and an inner fused-silica capillary. Under these conditions, the liquid flow rate can be reduced 15-fold from 7.5 microL/min to 0.5 microL/min. Studies of a 14-mer DNA oligonucleotide show no change in the charge-state distribution and quantity of adducted salt ions during the microspray process compared to pneumatically assisted electrospray mass spectrometry. The microspray ion source is less sensitive to the presence of solution buffers, and an 11-fold increase in integrated ion abundance from oligonucleotide analyte is observed with a 10 mM concentration of ammonium acetate, compared to pneumatically assisted nebulization (PAN). A > 100-fold increase in the duplex:single strand ratio for a 14-mer oligodeoxynucleotide and its complementary strand is observed using the microspray ion source relative to experiments performed with PAN. Studies of duplexes between DNA and a peptide nucleic acid suggest that this effect may be related to the degree of adduction of counterions to the DNA during ionization. PMID:8563016

Greig, M J; Gaus, H J; Griffey, R H

1996-01-01

45

Emittance studies of high intensity negative ion sources equipped with continuous surface cylindrical and spherical geometry tungsten ionizers  

SciTech Connect

A digitally controlled emittance measurement, data acquisition and processing system has been designed, implemented and used to determine emittances of negative ion beams extracted from high-intensity negative-ion sources equipped with cylindrical and spherical geometry cesium surface ionizers. Comparative studies indicate that the emittances of ion beams extracted from the source equipped with a spherical geometry ionizer are lower by 13% to 21% than those extracted from the source equipped with a cylindrical geometry ionizer. This difference may be attributable to geometric factors rather than differences in the sizes of the emission areas at the points of negative-ion generation. Studies reveal that the emittances of these sources are independent of ion mass for most of the materials investigated and independent of ion current over the range of ion currents used in these investigations (4..mu..A to 12 ..mu..A).

Alton, G.D.; McConnell, J.W.; Tajima, S.; Nelson, G.S.

1986-01-01

46

Sensitive monitoring of volatile chemical warfare agents in air by atmospheric pressure chemical ionization mass spectrometry with counter-flow introduction.  

PubMed

A new method for sensitively and selectively detecting chemical warfare agents (CWAs) in air was developed using counter-flow introduction atmospheric pressure chemical ionization mass spectrometry (MS). Four volatile and highly toxic CWAs were examined, including the nerve gases sarin and tabun, and the blister agents mustard gas (HD) and Lewisite 1 (L1). Soft ionization was performed using corona discharge to form reactant ions, and the ions were sent in the direction opposite to the airflow by an electric field to eliminate the interfering neutral molecules such as ozone and nitrogen oxide. This resulted in efficient ionization of the target CWAs, especially in the negative ionization mode. Quadrupole MS (QMS) and ion trap tandem MS (ITMS) instruments were developed and investigated, which were movable on the building floor. For sarin, tabun, and HD, the protonated molecular ions and their fragment ions were observed in the positive ion mode. For L1, the chloride adduct ions of L1 hydrolysis products were observed in negative ion mode. The limit of detection (LOD) values in real-time or for a 1 s measurement monitoring the characteristic ions were between 1 and 8 ?g/m(3) in QMS instrument. Collision-induced fragmentation patterns for the CWAs were observed in an ITMS instrument, and optimized combinations of the parent and daughter ion pairs were selected to achieve real-time detection with LOD values of around 1 ?g/m(3). This is a first demonstration of sensitive and specific real-time detection of both positively and negatively ionizable CWAs by MS instruments used for field monitoring. PMID:23339735

Seto, Yasuo; Kanamori-Kataoka, Mieko; Tsuge, Koichiro; Ohsawa, Isaac; Iura, Kazumitsu; Itoi, Teruo; Sekiguchi, Hiroyuki; Matsushita, Koji; Yamashiro, Shigeharu; Sano, Yasuhiro; Sekiguchi, Hiroshi; Maruko, Hisashi; Takayama, Yasuo; Sekioka, Ryoji; Okumura, Akihiko; Takada, Yasuaki; Nagano, Hisashi; Waki, Izumi; Ezawa, Naoya; Tanimoto, Hiroyuki; Honjo, Shigeru; Fukano, Masumi; Okada, Hidehiro

2013-03-01

47

Detection of aqueous phase chemical warfare agent degradation products by negative mode ion mobility time-of-flight mass spectrometry [IM(tof)MS  

Microsoft Academic Search

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass\\u000a spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined.\\u000a Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified\\u000a reference materials (CRM) of CWA degradation products for the detection

Wes E. Steiner; Charles S. Harden; Feng Hong; Steve J. Klopsch; Vincent M. McHugh

2006-01-01

48

Volume 52, number 3 CHEMICAL PHYSICS LETTERS 15 December 1977 MULTIPHOTON IONIZATION  

E-print Network

Volume 52, number 3 CHEMICAL PHYSICS LETTERS 15 December 1977 MULTIPHOTON IONIZATION: A METHOD state distribution of this molecule. A tunable dye laser is swept through the w.ivclen$h region of the Naz B-X system and positive ions are counted as a function of laser wavelength. Multiphoton ionization

Zare, Richard N.

49

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

50

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

51

Effect of negative air ionization on airborne transmission of Newcastle disease virus.  

PubMed

Four-week-old mixed-sex White Rock chickens were used in four experiments to determine the effect of negative air ion enrichment on airborne transmission of the Roakin strain of Newcastle disease virus (NDV). The experiments were conducted in specially constructed airborne disease transmission cabinets in which donor (upwind) chickens cannot contact susceptible (downwind) chickens because of physical separation by a "no man's land." Temperature and humidity were computer-controlled at 26.7 C and 50% relative humidity, and ventilation rates were manually adjusted from 0.34 to 1.36 m3/min (12 to 48 ft3/min). Donor chickens were inoculated with Roakin NDV by eyedrop and intranasal routes and placed in the upwind end of each cabinet. One day later, susceptible chickens were placed in the downwind end. Seroconversion (> or = 1:10 NDV hemagglutination-inhibition titer) was considered evidence of infection from inoculation (upwind) or airborne transmission (downwind). Commercial air ion generators were used either in the ends or in the "no man's land" of the treatment cabinets and operated at power supply voltages ranging from -8kV direct current to -15 kV direct current. The use of negative air ion generators reduced airborne transmission an average of 6.6% to 27.7% compared with the control cabinets. Significant (P < or = 0.05) reductions in transmission were obtained with some treatments. The greatest reduction in transmission was obtained with the higher power supply voltages (13.8% reduction) and when the ionizers were placed in the "no man's land" (27.7% reduction) between the upwind and downwind chickens. PMID:7702504

Mitchell, B W; King, D J

1994-01-01

52

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

53

Fundamentals of interaction of ionizing radiations with chemical, biochemical, and pharmaceutical systems  

Microsoft Academic Search

A literature review is presented of the chemical and biological effects ; of ionizing radiations with special reference to the pharmaceutical sciences. A ; review of the theoretical principles of interactions of high energy radiations ; with matter is presented with re gard to three stages of the process: physical, ; physiocochemical, and chemical. In a discussion of the irradiation

Stephen G. Schulman

1973-01-01

54

Detection of chemical weapon agents and simulants using chemical ionization reaction time-of-flight mass spectrometry.  

PubMed

Chemical ionization reaction time-of-flight mass spectrometry (CIR-TOF-MS) has been used for the analysis of prepared mixtures of chemical weapon agents (CWAs) sarin and sulfur mustard. Detection of the CWA simulants 2-chloroethyl ethyl sulfide, triethyl phosphate, and dimethyl methyl phosphonate has also been investigated. Chemical ionization of all the agents and simulants was shown to be possible using the CIR-TOF-MS technique with a variety of reagent ions, and the sensitivity was optimized by variation of instrument parameters. The ionization process was found to be largely unaffected by sample humidity levels, demonstrating the potential suitability of the method to a range of environmental conditions, including the analysis of CWAs in air and in the breath of exposed individuals. PMID:17894471

Cordell, Rebecca L; Willis, Kerry A; Wyche, Kevin P; Blake, Robert S; Ellis, Andrew M; Monks, Paul S

2007-11-01

55

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

56

Characterization of ceramides by low energy collisional-activated dissociation tandem mass spectrometry with negative-ion electrospray ionization  

Microsoft Academic Search

Negative-ion electrospray ionization tandem quadrupole mass spectrometry provides a useful method for the structural characterization\\u000a of ceramides. Fragment ions referring to the identities of the fatty acid substituent and of the long chain base of the molecules\\u000a are readily available and the structure of ceramides can be easily determined. A unique fragmentation pathway which leads\\u000a to formation of the fatty

Fong-F. u Hsu; John Turk

2002-01-01

57

Identifying alkylbenzene isomers with chemical ionization-proton exchange mass spectrometry  

SciTech Connect

Chemical ionization-proton exchange mass spectrometry (CIPE) allows the number of unsubstituted aromatic carbons in alkylbenzene isomers to be determined. Only the aromatic hydrogens undergo exchange with deuterium when deuterated water, methanol, or ethanol is used as the reagent gas. Chemical ionization with deuterated methanol gives an acceptable mass spectral background and allows the determination of the number of unsubstituted positions on the benzene ring yielding structural information often unavailable from conventional electron impact spectra. Structural isomers such as propyl-, methylethyl-, and trimethylbenzene can easily be identified. The comparison of CIPE spectra from standard compounds, which are often unavailable, is not required to determine the number of unsubstituted aromatic carbons in alkylbenzene isomers. The method also allows ortho and para to be distinguished from meta disubstituted alkylbenzenes. Deuteriomethanol chemical ionization is used to characterize alkylbenzenes in a complex and relatively well studied sample, diesel exhaust. 14 references, 3 figures, 3 tables.

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

1985-03-01

58

Fast Time Response Measurements of Aerosol Composition by Chemical Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Fast and accurate measurements of atmospheric aerosol composition is an important part of quantifying and understanding atmospheric pollution and its consequences. Such data can be used for studies of regional haze analysis, development of atmospheric models, atmospheric aerosol source apportionment and aerosol and gas interactions. This presentation describes the development of a new technique for the measurement of atmospheric aerosol composition. A negative ion Chemical Ionization Mass Spectrometry (CIMS) method has been used to perform 1 Hz aerosol composition measurements. A heated inlet is used to evaporate ambient aerosol with subsequent detection of the evolved gases. Two reagent ions, bromide and nitrate, have been used to selectively detect acidic components of the aerosols such as sulfate, nitrate, malonate, and oxalate. The CIMS sulfate measurements in ambient air were compared with a Particle into Liquid Sampler (PILS). These tests showed a high degree of correlation between the measurements and strongly suggest that the CIMS can measure sulfate with a high degree of selectivity and sensitivity. Further tests suggest that CIMS method may be able to also perform selective measurements of a few strong organic acids such as oxalic.

Hecobian, A.; Thompson, A.; Tanner, D.; Peltier, R.; Weber, R.; Huey, G.

2005-12-01

59

Direct Laser Ablation and Ionization of Solids for Chemical Analysis by Mass Spectrometry  

SciTech Connect

A laser ablation/ionization mass spectrometer system is described for the direct chemical analysis of solids. An Nd:YAG laser is used for ablation and ionization of the sample in a quadrupole ion trap operated in an ion-storage (IS) mode that is coupled with a reflectron time-of-flight mass spectrometer (TOF-MS). Single pulse experiments have demonstrated simultaneous detection of up to 14 elements present in glasses in the ppm range. However, detection of the components has produced non-stoichiometric results due to difference in ionization potentials and fractionation effects. Time-of-flight secondary ionization mass spectrometry (TOF-SIMS) was used to spatially map elemental species on the surface and provide further evidence of fractionation effects. Resolution (m/Dm) of 1500 and detection limits of approximately 10 pg have been achieved with a single laser pulse. The system configuration and related operating principles for accurately measuring low concentrations of isotopes are described.

Holt, J K; Nelson, E J; Klunder, G L

2005-09-02

60

Sample introduction and pressure measuring system for chemical ionization mass spectrometers  

Microsoft Academic Search

One of the difficulties with using chemical ionization mass spectrometry (CIMS) in magnetic sector instruments has been that of electrical dischargers through the gaseous sample between the ion source, which may be at potentials at 10kV and ground. A sample introduction method is presented to offset this. It was first used at the University of Nebraska, Lincoln on a modified

A. J. Illies; M. T. Bowers; G. G. Meisels

1981-01-01

61

[Development of a membrane inlet-single photon ionization/chemical ionization-mass spectrometer for online analysis of VOCs in water].  

PubMed

A home-made membrane inlet- single photon ionization/chemical ionization- time-of-flight mass spectrometer has been described. A vacuum ultraviolet (VUV) lamp with photon energy of 10.6 eV was used as the light source for single photon ionization (SPI). Chemical ionization (CI) was achieved through ion-molecule reactions with O2- reactant ions generated by photoelectron ionization. The two ionization modes could be rapidly switched by adjusting electric field in the ionization region within 2 s. Membrane inlet system used for rapid enrichment of volatile organic compounds (VOCs) in water was constructed by using a polydimethylsiloxane (PDMS) membrane with a thickness of 50 microm. A purge gas was added to accelerate desorption of analytes from the membrane surface. The purge gas could also help to prevent the pump oil back-streaming into the ionization region from the analyzer chamber and improve the signal to noise ratio (S/N). Achieved detection limits were 2 microg x L(-1) for methyl tert-butyl ether (MTBE) in SPI mode and 1 microg x L(-1) for chloroform in SPI-CI mode within 10 s analysis time, respectively. The instrument has been successfully applied to the rapid analysis of MTBE in simulated underground water nearby petrol station and VOCs in disinfected drinking water. The results indicate that the instrument has a great application prospect for online analysis of VOCs in water. PMID:22468530

Hua, Lei; Wu, Qing-Hao; Hou, Ke-Yong; Cui, Hua-Peng; Chen, Ping; Zhao, Wu-Duo; Xie, Yuan-Yuan; Li, Hai-Yang

2011-12-01

62

Fragmentation of allylmethylsulfide by chemical ionization: dependence on humidity and inhibiting role of water.  

PubMed

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

Maihom, Thana; Schuhfried, Erna; Probst, Michael; Limtrakul, Jumras; Märk, Tilmann D; Biasioli, Franco

2013-06-20

63

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

64

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

PubMed

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(2)V(-1)s(-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. PMID:21524145

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

2011-06-15

65

Quantification of flavonoids in black rice by liquid chromatography-negative electrospray ionization tandem mass spectrometry.  

PubMed

Systematic identification and structural characterization of flavonoids and their glycosides in bran extracts of seven Thai black rice varieties were performed by sequential uses of reversed-phase HPLC with a photodiode array detector and a combined electrospray ionization tandem mass spectrometer. Eleven flavonoids were detected, and six of these were found for the first time in rice bran. These were taxifolin-7-O-glucoside, myricetin-7-O-glucoside, isorhamnetin-3-O-acetylglucoside, isorhamnetin-7-O-rutinoside, 5,6,3',4',5'-pentahydroxyflavone-7-O-glucoside, and 5,3',4',5'-tetrahydroxyflavanone-7-O-glucoside. The quantitative results revealed that different rice varieties possessed flavonoids in different concentrations. The most abundant glycoside derivative of flavonoids widely distributed among the rice varieties was monoglucoside, such as quercetin-3-O-glucoside, isorhamnetin-3-O-glucoside, and isorhamnetin-3-O-glucoside. PMID:23121250

Sriseadka, Tinakorn; Wongpornchai, Sugunya; Rayanakorn, Mongkon

2012-11-28

66

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

67

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

68

Chemical imaging of artificial fingerprints by desorption electro-flow focusing ionization mass spectrometry.  

PubMed

Desorption electro-flow focusing ionization (DEFFI) mass spectrometry was used to image chemical distributions of endogenous, e.g., fatty acids, and trace exogenous compounds, e.g., explosives, narcotics and lotions, in deposited and lifted artificial fingerprints, directly from forensic lift tape. An artificial fingerprint mold and synthetic fingerprint material were incorporated for the controlled deposition of material for technique demonstration and evaluation. PMID:24566545

Forbes, Thomas P; Sisco, Edward

2014-06-21

69

Radioimmunoassay and chemical ionization/mass spectrometry compared for plasma cortisol determination  

SciTech Connect

A method is described for determination of cortisol in plasma and urine, based on chemical ionization/mass spectrometry with deuterium-labeled cortisol as the internal standard. The within-run precision (CV) was 2.5-5.7%, the between-run precision 4.6%. Results by this method were compared with those by a radioimmunological method (RIANEN Cortisol, New England Nuclear) for 395 plasma samples. The latter method gave significantly higher (approx. 25%) cortisol values.

Lindberg, C. (AB Draco, Lund, Sweden); Johnson, S.; Hedner, P.; Gustafsson, A.

1982-01-01

70

Analysis and characterization of sophorolipids by liquid chromatography with atmospheric pressure chemical ionization  

Microsoft Academic Search

Summary  A reversed phase high performance liquid chromatographic method combined with atmospheric pressure chemical ionization mass\\u000a detection (LC\\/APCI-MS) has been developed for the separation and analysis of sophorolipids produced byC. bombicola when grown on fatty acid mixtures. Using this method it was found that the incorporation of palmitic, linoleic, and linolenic\\u000a acids into the sophorolipid structure was dependent on the initial

A. Nuñez; R. Ashby; T. A. Foglia; D. K. Y. Solaiman

2001-01-01

71

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

72

Supersonic jet/multiphoton ionization spectrometry of chemical species resulting from thermal decomposition and laser ablation of polymers  

SciTech Connect

The chemical species resulting from thermal decomposition and laser ablation of polymers are measured by excitation/fluorescence and multiphoton ionization/mass spectrometries after supersonic jet expansion for rotational cooling to simply the optical spectrum. The signal of minor chemical species occurred is strongly enhanced by resonant excitation and multiphoton ionization, and even the isomer can be clearly differentiated. For example, p-cresol occurred by thermal decomposition of polycarbonate is detected selectively by mass-selected resonant multiphoton ionization spectrometry. Various chemical species occurred by laser ablation of even a polystyrene foam are also measured by this technique.

Hozumi, Masami; Murata, Yoshiaki; Cheng-Huang Lin; Imasaka, Totaro [Department of Chemical Science and Technology, Faculty of Engineering, Hakozaki, Higashi-Ku, Fukuoka 812 (Japan)

1995-04-01

73

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

NASA Astrophysics Data System (ADS)

Laser-induced acoustic desorption (LIAD) was successfully coupled to a conventional atmospheric pressure chemical ionization (APCI) source in a commercial 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. From the four APCI reagent systems tested, neat carbon disulfide provided the best results. 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 but minor amount of fragmentation was observed for these two 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 predominantly form stable molecular ions.

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

2011-03-01

74

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...

75

Chemical analysis of positive and negative plates, a survey. [nickel cadmium batteries  

NASA Technical Reports Server (NTRS)

Regular arrays of 1 inch discs cut from chemically impregnated positive and negative plates were sent to various contractors and government organizations for chemical analysis in order to determine whether there is consistency in analysis. Techniques used included NASA procedures as specified, variations, wet chemical techniques, and atomic absorption. The weight, thickness of disc, and active material quantity as measured by four respondents are discussed.

Halpert, G.

1978-01-01

76

Detection of chemical warfare agent degradation products in foods using liquid chromatography coupled to inductively coupled plasma mass spectrometry and electrospray ionization mass spectrometry  

Microsoft Academic Search

The following work presents the exploration of three chromatographic separations in combination with inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of chemical warfare agent degradation products (CWADPs). The robust ionization of ICP is virtually matrix independent thus enabling the examination of sample matrices generally considered too complicated for analysis by electrospray ionization (ESI) or atmospheric pressure chemical ionization

Kevin M. Kubachka; Douglas D. Richardson; Douglas T. Heitkemper; Joseph A. Caruso

2008-01-01

77

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

78

Chemical derivatization for electrospray ionization mass spectrometry. 1. Alkyl halides, alcohols, phenols, thiols, and amines  

SciTech Connect

Derivatization strategies and specific derivatization reactions for conversion of simple alkyl halides, alcohols, phenols, thiols, and amines to ionic or solution-ionizable derivatives, that is [open quotes]electrospray active[close quotes] (ES-active) forms of the analyte, are presented. Use of these reactions allows detection of analytes among those listed that are not normally amenable to analysis by electrospray ionization mass spectrometry (ES-MS). In addition, these reactions provide for analysis specificity and flexibility through functional group specific derivatization and through the formation of derivatives that can be detected in positive ion or in negative ion mode. For a few of the functional groups, amphoteric derivatives are formed that can be analyzed in either positive or negative ion modes. General synthetic strategies for transformation of members of these five compound classes to ES-active species are presented along with illustrative examples of suitable derivatives. Selected derivatives were prepared using model compounds and the ES mass spectra obtained for these derivatives are discussed. The analytical utility of derivatization for ES-MS analysis is illustrated in three experiments: (1) specific detection of the major secondary alcohol in oil of peppermint, (2) selective detection of phenols within a synthetic mixture of phenols, and (3) identification of the medicinal amines within a commercially available cold medication as primary, secondary or tertiary. 65 refs., 3 figs., 3 tabs.

Quirke, J.M.E.; Adams, C.L.; Van Berkel, G.J. (Oak Ridge National Lab., TN (United States))

1994-04-15

79

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

80

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

81

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

82

Waterborne chemical compounds in tropical macroalgae: positive and negative cues for larval settlement  

Microsoft Academic Search

Settlement sites of marine invertebrate larvae are frequently influenced by positive or negative cues, many of which are chemical in nature. Following from the observation that many shallow-water, Hawai'ian marine macroalgae are free of fouling by sessile invertebrates, we predicted that the algae are chemically protected and dependent on either surface-bound or continuously released soluble compounds to deter settling invertebrate

L. J. Walters; M. G. Hadfield; C. M. Smith

1996-01-01

83

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

84

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

85

Simultaneous LC/MS analysis of hexachlorobenzene and pentachlorophenol by atmospheric pressure chemical ionization (APCI) and photoionization (APPI) methods.  

PubMed

The simultaneous LC/MS analyses of hexachlorobenzene (HCB) and pentachlorophenol (PCP), two dioxin precursors were studied by both atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization mass spectrometry (APPI/MS). The optimum LC/MS conditions of the simultaneous analysis were determined for these two compounds with different polarity. Ionization by APPI was found to be more effective than by APCI, and is thus a better ionization method for analysis of the two compounds. Using LC/APPI/MS we can achieve the simultaneous analysis of HCB and PCP at ppb levels. PMID:19907098

Osaka, Issey; Yoshimoto, Arifumi; Nozaki, Kazuyoshi; Moriwaki, Hiroshi; Kawasaki, Hideya; Arakawa, Ryuichi

2009-11-01

86

Qualitative analysis of some carboxylic acids by ion-exclusion chromatography with atmospheric pressure chemical ionization mass spectrometric detection.  

PubMed

A simple, selective and sensitive method for the determination of carboxylic acids has been developed. A mixture of formic, acetic, propionic, valeric, isovaleric, isobutyric, and isocaproic acids has been separated on a polymethacrylate-based weak acidic cation-exchange resin (TSK gel OA pak-A) based on an ion-exclusion chromatographic mechanism with detection using UV-photodiode array, conductivity and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). A mobile phase consisting of 0.85 mM benzoic acid in 10% aqueous methanol (pH 3.89) was used to separate the above carboxylic acids in about 40 min. For LC-MS, the APCI interface was used in the negative ionization mode. Linear plots of peak area versus concentration were obtained over the range 1-30 mM (r2=0.9982) and 1-30 mM (r2=0.9958) for conductimetric and MS detection, respectively. The detection limits of the target carboxylic acids calculated at S/N=3 ranged from 0.078 to 2.3 microM for conductimetric and photometric detection and from 0.66 to 3.82 microM for ion-exclusion chromatography-APCI-MS. The reproducibility of retention times was 0.12-0.16% relative standard deviation for ion-exclusion chromatography and 1.21-2.5% for ion-exclusion chromatography-APCI-MS. The method was applied to the determination of carboxylic acids in red wine, white wine, apple vinegar, and Japanese rice wine. PMID:12108651

Helale, Murad I H; Tanaka, Kazuhiko; Taoda, Hiroshi; Hu, Wenzhi; Hasebe, Kiyoshi; Haddad, Paul R

2002-05-17

87

Differeniation of Aroclors in environmental samples using negative ion chemical ionization (NICI) mass spectrometry  

SciTech Connect

Environmental samples suspected of containing polychlorinated biphenyls (PCB) and analyzed by EPA Method 8080 frequently contain non-PCB components, such as phthalates, PAH's, or organochlorine pesticides. The presence of these interferences can often obscure the GC/ECD patterns and cause problems in differentiating the Aroclor types by visual inspection. Since Method 8080 requires the identification of Aroclor types in order to trace the sources of PCB occurrences, NICI detection was used to provide additional parameters for discriminating PCB congeners from interferences. In this study, a pattern recognition method has been developed to classify the types of Aroclors for environmental samples. A computer program written in BASIC has been implemented to facilitate Aroclor classification using the NICI ion abundance measurement for PCB congeners. NICI measurements on Aroclor standards were used as training data set to develop classification methods for environmental samples. PCB contaminated oil or soil samples were either extracted of diluted with hexane and analyzed in the same manner as the standards. This sequential classification method classified all Aroclors in the training set correctly. A set of 15 environmental samples with known Aroclor types were also correctly classified.

Ma, C.Y.; Bayne, C.K.; Maskarinec, M.P.

1991-01-01

88

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

89

Analysis of isomeric polycyclic aromatic hydrocarbons by charge-exchange chemical ionization mass spectrometry  

SciTech Connect

Charge-exchange chemical ionization mass spectrometry (using a 15% mixture of methane in argon) yields abundant M/sup +/, M + H/sup +/, M + C/sub 2/H/sub 5//sup +/ ions of polycyclic aromatic hydrocarbons (PAH). On the basis of the relative intensities of the M + H/sup +/ ion to the M/sup +/ ion, this technique can differentiate, in a predictable manner, isomeric structures of PAH. The operating conditions were evaluated and optimized; the most significant contributions to the variations in the (M + H)/sup +//M/sup +/ ratios are the temperature, pressure, and condition of the ion source. The optimum ion source temperature (250/sup 0/C) and pressure (0.8 torr) are easily controlled and regulated. The variable contamination of the ion source is compensated by an internal standard 1,2,3,5-tetrafluorobenzene. The analyses of Standard Reference Materials 1648 and 1649 (air particulate samples) and a carbon black extract are reported. Triphenylene and chrysene, although not chromatographically resolved, can be quantitated by using this technique. The identification of acephenanthrylene based on the measurement of ratios and calculated ionization potentials is also presented.

Simonsick, W.J. Jr.; Hites, R.A.

1984-12-01

90

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

91

Soft ionization chemical analysis of secondary organic aerosol from green leaf volatiles emitted by turf grass.  

PubMed

Globally, biogenic volatile organic compound (BVOC) emissions contribute 90% of the overall VOC emissions. Green leaf volatiles (GLVs) are an important component of plant-derived BVOCs, including cis-3-hexenylacetate (CHA) and cis-3-hexen-1-ol (HXL), which are emitted by cut grass. In this study we describe secondary organic aerosol (SOA) formation from the ozonolysis of dominant GLVs, their mixtures and grass clippings. Near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS) was used for chemical analysis of the aerosol. The chemical profile of SOA generated from grass clippings was correlated with that from chemical standards of CHA and HXL. We found that SOA derived from HXL most closely approximated SOA from turf grass, in spite of the approximately 5× lower emission rate of HXL as compared to CHA. Ozonolysis of HXL results in formation of low volatility, higher molecular weight compounds, such as oligomers, and formation of ester-type linkages. This is in contrast to CHA, where the hydroperoxide channel is the dominant oxidation pathway, as oligomer formation is inhibited by the acetate functionality. PMID:24666343

Jain, Shashank; Zahardis, James; Petrucci, Giuseppe A

2014-05-01

92

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

93

Qualitative gas chromatography-mass spectrometry analyses using amines as chemical ionization reagent gases.  

PubMed

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. PMID:24114260

Little, James L; Howard, Adam S

2013-12-01

94

Online atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-IT-MSn) for measuring organic acids in concentrated bulk aerosol - a laboratory and field study  

NASA Astrophysics Data System (ADS)

The field application of an aerosol concentrator in conjunction with an atmospheric pressure chemical ionization ion trap mass spectrometer (APCI-IT-MS) at the boreal forest station SMEAR II at Hyytiälä, Finland, is demonstrated in this study. APCI is a soft ionization technique allowing online measurements of organic acids in the gas and particle phase. The detection limit for the acid species in the particle phase was increased by a factor of 7.5 to 11 (e.g. ~40 ng m-3 for pinonic acid) by using the miniature Versatile Aerosol Concentration Enrichment System (mVACES) upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic organic acid standards - pinic acid and pinonic acid. Pinic acid was used as a surrogate for the quantification of the total amount of organic acids in the ambient aerosol based on the total signal intensities in the negative ion mode. The results were compared with the total organic signal of a C-ToF-AMS during the HUMPPA-COPEC 2010 field campaign. The campaign average contribution of organic acids measured by APCI-IT-MS to the total sub-micron organic aerosol mass was estimated to be about 60%. Very good correlation between APCI-IT-MS and C-ToF-AMS (Pearson's R = 0.94) demonstrates soft ionization mass spectrometry as a complimentary technique to AMS with electron impact ionization. MS2 studies of specific m/z ratios recorded during the HUMPPA-COPEC 2010 field campaign were compared to MS2 studies of selected monoterpene oxidation products formed in simulation chamber experiments. The comparison of the resulting fragments shows that oxidation products of the main VOCs emitted at Hyytiälä (?-pinene and ?3-carene) cannot account for all of the measured fragments, which illustrates the complexity of ambient aerosol and possibly indicates unidentified or underestimated biogenic SOA precursor in the boreal forest.

Vogel, A. L.; Äijälä, M.; Brüggemann, M.; Ehn, M.; Junninen, H.; Petäjä, T.; Worsnop, D. R.; Kulmala, M.; Williams, J.; Hoffmann, T.

2012-08-01

95

Kinetics of ion-molecule reactions with dimethyl methylphosphonate at 298 K for chemical ionization mass spectrometry detection of GX.  

PubMed

Kinetics studies of a variety of positive and negative ions reacting with the GX surrogate, dimethyl methylphosphonate (DMMP), were performed. All protonated species reacted rapidly, that is, at the collision limit. The protonated reactant ions created from neutrals with proton affinities (PAs) less than or equal to the PA for ammonia reacted exclusively by nondissociative proton transfer. Hydrated H(3)O(+) ions also reacted rapidly by proton transfer, with 25% of the products from the second hydrate, H(3)O(+)(H(2)O)(2), forming the hydrated form of protonated DMMP. Both methylamine and triethylamine reacted exclusively by clustering. NO(+) also clustered with DMMP at about 70% of the collision rate constant. O(+) and O(2)(+) formed a variety of products in reactions with DMMP, with O(2)(+) forming the nondissociative charge transfer product about 50% of the time. On the other hand, many negative ions were less reactive, particularly, SF(5)(-), SF(6)(-), CO(3)(-), and NO(3)(-). However, F(-), O(-), and O(2)(-) all reacted rapidly to generate m/z = 109 amu anions (PO(3)C(2)H(6)(-)). In addition, product ions with m/z = 122 amu from H(2)(+) loss to form H(2)O were the dominant ions produced in the O(-) reaction. NO(2)(-) underwent a slow association reaction with DMMP at 0.4 Torr. G3(MP2) calculations of the ion energetics properties of DMMP, sarin, and soman were also performed. The calculated ionization potentials, proton affinities, and fluoride affinities were consistent with the trends in the measured kinetics and product ion branching ratios. The experimental results coupled with the calculated ion energetics helped to predict which ion chemistry would be most useful for trace detection of the actual chemical agents. PMID:19385679

Midey, Anthony J; Miller, Thomas M; Viggiano, A A

2009-04-30

96

Simultaneous determination of bisphenol A, triclosan, and tetrabromobisphenol A in human serum using solid-phase extraction and gas chromatography-electron capture negative-ionization mass spectrometry  

Microsoft Academic Search

This study aimed at optimizing and validating a sensitive method for simultaneous determination of bisphenol A (BPA), triclosan\\u000a (TCS), and tetrabromobisphenol A (TBBPA) in human serum using solid-phase extraction (SPE) and gas chromatography coupled\\u000a to electron-capture negative-ionization mass spectrometry (GC-ECNI\\/MS). Sample preparation involved denaturation of serum\\u000a proteins with formic acid followed by SPE on an Oasis HLB cartridge. Fractionation was

Alin C. Dirtu; Laurence Roosens; Tinne Geens; Adriana Gheorghe; Hugo Neels; Adrian Covaci

2008-01-01

97

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

98

Desorption electrospray ionization mass spectrometry reveals surface-mediated antifungal chemical defense of a tropical seaweed  

PubMed Central

Organism surfaces represent signaling sites for attraction of allies and defense against enemies. However, our understanding of these signals has been impeded by methodological limitations that have precluded direct fine-scale evaluation of compounds on native surfaces. Here, we asked whether natural products from the red macroalga Callophycus serratus act in surface-mediated defense against pathogenic microbes. Bromophycolides and callophycoic acids from algal extracts inhibited growth of Lindra thalassiae, a marine fungal pathogen, and represent the largest group of algal antifungal chemical defenses reported to date. Desorption electrospray ionization mass spectrometry (DESI-MS) imaging revealed that surface-associated bromophycolides were found exclusively in association with distinct surface patches at concentrations sufficient for fungal inhibition; DESI-MS also indicated the presence of bromophycolides within internal algal tissue. This is among the first examples of natural product imaging on biological surfaces, suggesting the importance of secondary metabolites in localized ecological interactions, and illustrating the potential of DESI-MS in understanding chemically-mediated biological processes. PMID:19366672

Lane, Amy L.; Nyadong, Leonard; Galhena, Asiri S.; Shearer, Tonya L.; Stout, E. Paige; Parry, R. Mitchell; Kwasnik, Mark; Wang, May D.; Hay, Mark E.; Fernandez, Facundo M.; Kubanek, Julia

2009-01-01

99

Production and Utilization of CO3- Produced by a Corona Discharge in Air for Atmospheric Pressure Chemical Ionization  

SciTech Connect

Atmospheric pressure chemical ionization is a multistep ionization process used in mass spectrometry and ion mobility spectrometry. The formation of product ions depends upon interactions with the analyte and the reactant ion species formed in the ionization source. The predominant reactant ion observed in a point-to-plane corona discharge in air occurs at m/z 60. There have been multiple references in the literature to the identity of this ion with some disagreement. It was postulated to be either CO3- or N2O2-. The identity of this ion is important as it is a key to the ionization of analytes. It was determined here to be CO3- through the use of 18O labeled oxygen. Further confirmation was provided through MS/MS studies. The ionization of nitroglycerine (NG) with CO3- produced the adduct NG•CO3-. This was compared to ionization with NO3- and Cl- reactant ions that also formed adducts with NG. The fragmentation patterns of these three adducts provides insight into the charge distribution and indicates that CO3- has a relatively high electron affinity similar to that of nitrate.

Ewing, Robert G.; Waltman, Melanie J.

2010-12-14

100

Chemical imaging of trichome specialized metabolites using contact printing and laser desorption/ionization mass spectrometry.  

PubMed

Cell transfer by contact printing coupled with carbon-substrate-assisted laser desorption/ionization was used to directly profile and image secondary metabolites in trichomes on leaves of the wild tomato Solanum habrochaites. Major specialized metabolites, including acyl sugars, alkaloids, flavonoids, and terpenoid acids, were successfully detected in positive ion mode or negative ion mode, and in some cases in both modes. This simple solvent-free and matrix-free sample preparation for mass spectrometry imaging avoids tedious sample preparation steps, and high-spatial-resolution images were obtained. Metabolite profiles were generated for individual glandular trichomes from a single Solanum habrochaites leaf at a spatial resolution of around 50 ?m. Relative quantitative data from imaging experiments were validated by independent liquid chromatography-mass spectrometry analysis of subsamples from fresh plant material. The spatially resolved metabolite profiles of individual glands provided new information about the complexity of biosynthesis of specialized metabolites at the cellular-resolution scale. In addition, this technique offers a scheme capable of high-throughput profiling of metabolites in trichomes and irregularly shaped tissues and spatially discontinuous cells of a given cell type. PMID:24220760

Li, Chao; Wang, Zhenzhen; Jones, A Daniel

2014-01-01

101

Herbert P. Broida Prize Lecture: Probing chemical dynamics with negative ion photodetachment  

NASA Astrophysics Data System (ADS)

Photoelectron spectroscopy and its variants have been used in our laboratory to study diverse phenomena in chemical dynamics, including transition state spectroscopy, the electronic and vibrational spectroscopy of clusters, the photodissociation of reactive free radicals, hydrated electron dynamics in clusters and liquid jets, and the ultrafast dynamics of helium nanodroplets. This talk will focus on two examples of this type of work: slow electron velocity map imaging (SEVI) of trapped and cooled negative ions, and time-resolved photoelectron spectroscopy (TRPES) of negative ions. SEVI of cold ions represents a powerful means of performing high resolution photoelectron spectroscopy on complex species. Time-resolved radiation chemistry in nucleobases will be carried out with TRPES. In this work, starting with iodide-nucleobase complexes, we inject electrons into low-lying unoccupied orbitals of the nucleobase and follow the ensuing dynamics.

Neumark, Daniel

2013-03-01

102

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

103

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. Our results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of one minute it is ~6 × 104 molecules of H2SO4 per cm3. 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.

2010-11-01

104

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

105

Shrinking droplets in electrospray ionization and their influence on chemical equilibria.  

PubMed

We investigated how chemical equilibria are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF) and phase Doppler anemometry (PDA). The motivation for this study was the increasing number of publications in which electrospray ionization mass spectrometry is used for binding constant determination. The PDA was used to monitor droplet size and velocity, whereas LIF was used to monitor fluorescent analytes within the electrospray droplets. Using acetonitrile as solvent, we found an average initial droplet diameter of 10 microm in the electrospray. The PDA allowed us to follow the evolution of these droplets down to a size of 1 microm. Rhodamine B-sulfonylchloride was used as a fluorescent analyte within the electrospray. By spatially resolved LIF it was possible to probe the dimerization equilibrium of this dye. Measurements at different spray positions showed no influence of the decreasing droplet size on the monomer-dimer equilibrium. However, with the fluorescent dye pair DCM and oxazine 1 it was shown that a concentration increase does occur within electrosprayed droplets, using fluorescence resonance energy transfer as a probe for the average pair distance. PMID:17112736

Wortmann, Arno; Kistler-Momotova, Anna; Zenobi, Renato; Heine, Martin C; Wilhelm, Oliver; Pratsinis, Sotiris E

2007-03-01

106

Bake condition effect on hybrid lithography process for negative-tone chemically amplified resists  

NASA Astrophysics Data System (ADS)

This paper presents the process optimization study of negative tone Chemically Amplified Resists (CAR) under E-Beam exposure. The importance of post apply bake temperature choice on resolution is underlined. The process study determines the process window in which optimal conditions of both post apply and post exposure bake steps are defined and present a method to define more precisely the thermal cross-linking onset. Finally lithographic performances of CARs are studied and we show that resolution can be pushed down to 40 nm.

Pain, Laurent; Sala, F.; Higgins, C.; Dal'zotto, B.; Tedesco, Serge V.

2000-06-01

107

Negative-tone block copolymer lithography by in situ surface chemical modification.  

PubMed

Negative-tone block copolymer (BCP) lithography based on in situ surface chemical modification is introduced as a highly efficient, versatile self-assembled nanopatterning. BCP blends films consisting of end-functionalized low molecular weight poly(styrene-ran-methyl methacrylate) and polystyrene-block-Poly(methyl methacylate) can produce surface vertical BCP nanodomains on various substrates without prior surface chemical treatment. Simple oxygen plasma treatment is employed to activate surface functional group formation at various substrates, where the end-functionalized polymers can be covalently bonded during the thermal annealing of BCP thin films. The covalently bonded brush layer mediates neutral interfacial condition for vertical BCP nanodomain alignment. This straightforward approach for high aspect ratio, vertical self-assembled nanodomain formation facilitates single step, site-specific BCP nanopatterning widely useful for various substrates. Moreover, this approach is compatible with directed self-assembly approaches to produce device oriented laterally ordered nanopatterns. PMID:24912807

Kim, Bong Hoon; Byeon, Kyeong-Jae; Kim, Ju Young; Kim, Jinseung; Jin, Hyeong Min; Cho, Joong-Yeon; Jeong, Seong-Jun; Shin, Jonghwa; Lee, Heon; Kim, Sang Ouk

2014-10-01

108

Pulsed large volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry for simultaneous determination of typical halogenated persistent organic pollutants  

Microsoft Academic Search

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry\\u000a (pLVI-GC\\/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs).\\u000a By monitoring the characteristic ions of large mass-to-charge ratio (m\\/z) for each of the H-POPs rather than the chlorine and\\/or bromine ions, this method avoided the possible interferences arising\\u000a from the H-POPs

Yuli Zhao; Limin Yang; Qiuquan Wang

2007-01-01

109

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

110

Determination of Organic Acids in Ground Water by Liquid Chromatography\\/Atmospheric Pressure Chemical Ionization\\/Mass Spectrometry  

Microsoft Academic Search

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),

Jiasong Fang; Michael J. Barcelona

1999-01-01

111

Time-of-flight secondary ion mass spectrometry with energetic cluster ion impact ionization for highly sensitive chemical structure characterization  

NASA Astrophysics Data System (ADS)

Energetic cluster ions with energies of the order of sub MeV or greater were applied to time-of-flight (TOF) secondary ion (SI) mass spectrometry. This gave various advantages including enhancement of SIs required for chemical structure characterization and prevention of charging effects in SI mass spectra for organic targets. We report some characteristic features of TOF SI mass spectrometry using energetic cluster ion impact ionization and discuss two future applications of it.

Hirata, K.; Saitoh, Y.; Chiba, A.; Yamada, K.; Narumi, K.

2013-11-01

112

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

113

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

114

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

115

Online atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-IT-MSn) for measuring organic acids in concentrated bulk aerosol - a laboratory and field study  

NASA Astrophysics Data System (ADS)

The field application of an aerosol concentrator in conjunction with an atmospheric pressure chemical ionization ion trap mass spectrometer (APCI-IT-MS) at the boreal forest station SMEAR II at Hyytiälä, Finland, is demonstrated in this study. APCI is a soft-ionization technique allowing online measurements of organic acids in the gas and particle phase. The detection limit for the acid species in the particle phase was improved by a factor of 7.5 to 11 (e.g. ∼40 ng m3 for pinonic acid) by using the miniature versatile aerosol concentration enrichment system (mVACES) upstream of the mass spectrometer. The APCI-IT-MS was calibrated in the negative ion mode with two biogenic organic acid standards - pinic acid and pinonic acid. Pinic acid was used as a surrogate for the quantification of the total amount of organic acids in the ambient aerosol based on the total signal intensities in the negative ion mode. The results were compared with the total organic signal of a C-ToF-AMS during the HUMPPA-COPEC 2010 field campaign. The campaign average contribution of organic acids measured by APCI-IT-MS to the total submicron organic aerosol mass was estimated to be about 60%, based on the response of pinic acid. Very good correlation between APCI-IT-MS and C-ToF-AMS (Pearson's R = 0.94) demonstrates soft-ionization mass spectrometry as a complimentary technique to AMS with electron impact ionization. MS2 studies of specific m/z ratios recorded during the HUMPPA-COPEC 2010 field campaign were compared to MS2 studies of selected monoterpene oxidation products formed in simulation chamber experiments. The comparison of the resulting fragments shows that oxidation products of the main VOCs emitted at Hyytiälä (?-pinene and ?3-carene) cannot account for all of the measured fragments. Possible explanations for those unaccounted fragments are the presence of unidentified or underestimated biogenic SOA precursors, or that different products are formed by a different oxidant mixture of the ambient air compared to the chamber ozonolysis.

Vogel, A. L.; Äijälä, M.; Brüggemann, M.; Ehn, M.; Junninen, H.; Petäjä, T.; Worsnop, D. R.; Kulmala, M.; Williams, J.; Hoffmann, T.

2013-02-01

116

Matrix interference-free method for the analysis of small molecules by using negative ion laser desorption/ionization on graphene flakes.  

PubMed

This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [M-H](-) ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [M+Na](+), potassium adduct [M+K](+), double sodium adduct [M+2Na-H](+), double potassium adduct [M+2K-H](+), as well as sodium and potassium mixed adduct [M+Na+K-H](+). Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules. PMID:21428301

Lu, Minghua; Lai, Yongquan; Chen, Guonan; Cai, Zongwei

2011-04-15

117

Negative Magnetoresistance of Indium Tin Oxide Nanoparticle Thin Films Grown by Chemical Thermolysis  

NASA Astrophysics Data System (ADS)

To clarify the electrical transport properties of nanostructured thin films, tin-doped indium oxide (ITO) nanoparticle (NP) solution-processed films were fabricated. An air-atmosphere, simple chemical thermolysis method was used to grow the ITO NPs, and the structural and electrical properties of spin-coated granular ITO NP films were investigated. X-ray diffraction measurements showed clear observation of the cubic indium oxide (222) diffraction peak, and films with a smaller Sn concentration were shown to have a better crystalline quality. We further explored the physical origin of the sign of the magnetoresistance (MR) in the variable-range hopping (VRH) region. A negative MR under a magnetic field perpendicular to the film surface increases with decreasing Sn concentration, and these results can be explained by the forward interference model in the VRH region. A larger negative MR is attributed to longer localization and hopping lengths, and better crystallinity. Thus, ITO NP thin films produced by this method are attractive candidates for oxide-based diluted magnetic semiconductors and other electronic devices.

Fujimoto, Akira; Yoshida, Kota; Higaki, Tomohiro; Kimura, Yuta; Nakamoto, Masami; Kashiwagi, Yukiyasu; Yamamoto, Mari; Saitoh, Masashi; Ohno, Toshinobu; Furuta, Shinya

2013-02-01

118

In pursuit of negative Fukui functions: examples where the highest occupied molecular orbital fails to dominate the chemical reactivity.  

PubMed

In our quest to explore molecules with chemically significant regions where the Fukui function is negative, we explored reactions where the frontier orbital that indicates the sites for electrophilic attack is not the highest occupied molecular orbital. The highest occupied molecular orbital (HOMO) controls the location of the regions where the Fukui function is negative, supporting the postulate that negative values of the Fukui function are associated with orbital relaxation effects and nodal surfaces of the frontier orbitals. Significant negative values for the condensed Fukui function, however, were not observed. PMID:23090502

Echegaray, Eleonora; Cárdenas, Carlos; Rabi, Sandra; Rabi, Nataly; Lee, Sungmin; Zadeh, Farnaz Heidar; Toro-Labbe, Alejandro; Anderson, James S M; Ayers, Paul W

2013-07-01

119

Analysis of nucleic acids by capillary ion-pair reversed-phase HPLC coupled to negative-ion electrospray ionization mass spectrometry.  

PubMed

Ion-pair reversed-phase high-performance liquid chromatography was successfully coupled to negative-ion electrospray ionization mass spectrometry by using 60 × 0.20 mm i.d. capillary columns packed with 2.3-?m micropellicular, octadecylated poly(styrene/divinylbenzene) particles as stationary phase and gradients of acetonitrile in 50 mM aqueous triethylammonium bicarbonate as mobile phase. Systematic variation of the eluent composition, such as concentration of ion-pair reagent, anion in the ion-pair reagent, solution pH, and acetonitrile concentration led to the conclusion that most parameters have opposite effects on chromatographic and mass spectrometric performances. The use of acetonitrile as sheath liquid enabled the rapid and highly efficient separation and detection of phosphorylated and nonphosphorylated oligonucleotides ranging in size from 8 to 40 nucleotides. High-quality full-scan mass spectra showing little cation adduction were acquired from which the molecular masses of the separated oligonucleotides were calculated with an accuracy of 0.011%. With calibration curves being linear over at least 2 orders of magnitude, the lower limits of detection for a oligodeoxythymidine 16-mer were 104 fmol with full scan and 710 amol with selected-ion-monitoring data acquisition. The potential of ion-pair reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry was demonstrated for mixed-sequence oligomers by the characterization of a reaction mixture from solid-phase synthesis of a 40-mer oligonucleotide. PMID:21662880

Huber, C G; Krajete, A

1999-09-01

120

Determination of emerging and priority industrial pollutants in surface water and wastewater by liquid chromatography-negative electrospray ionization tandem mass spectrometry.  

PubMed

A method for the simultaneous determination of six perfluoroalkyl compounds (perfluorooctanesulfonic acid (PFOS) and five perfluoroalkyl carboxylic acids), five phenolic compounds (nonylphenol (NP), bisphenol A (BPA), and methyl-, ethyl- and propylparabens), and the brominated flame retardant hexabromocyclododecane (HBCDD) in surface water and effluent wastewater has been developed. The selected pollutants include eight of the industrial pollutants (PFOS and derivatives, NP, and HBCDD) that could be regulated in surface water according to an European Union Directive proposal and four compounds of great concern because their estrogenicity (BPA and parabens). The method is based on solid-phase extraction and determination by high-performance liquid chromatography-triple quadrupole mass spectrometry in negative electrospray ionization mode. Method quantitation limits of NP, PFOS and derivatives, and HBCDD allow its application for routinely control of surface water according to the EU proposal of directive. PMID:24633504

Martín, Julia; Camacho-Muñoz, Dolores; Santos, Juan Luis; Aparicio, Irene; Alonso, Esteban

2014-06-01

121

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

122

Chemical abundances and ionization in sub-Damped Lyman-alpha absorbers at z < 1.5  

NASA Astrophysics Data System (ADS)

The chemical composition of galaxies provide important clues into galaxy formation and evolution. Quasar (QSO) absorption line systems offer a unique window into the high redshift Universe and the properties of normal galaxies at high redshift. QSO absorbers have long been used to study distant galaxies and the intergalactic medium (IGM). The Damped Lyman-a systems (DLAs), with neutral Hydrogen column densities of log N H I > 20.3, and sub-Damped Lyman-a systems (sub-DLAs) with 19.0 < log N H I < 20.3 contain the majority of the neutral gas in the Universe at high redshift, probe metallicities over ~90% of the cosmic history, and are believed to be the progenitors of modern day galaxies. Models of the chemical evolution of galaxies predict that the mean metallicity of galaxies should reach a solar value by z ~ 0 due to the ongoing cycles of star formation which enrich the galaxy with heavy elements. The DLA systems which have been the preferred class of absorbers for these investigations however appear to be metal poor at all redshifts, and show little evolution in their metallicity, contradicting the models of chemical evolution, the "missing metals problem". We have amassed a sample of 32 sub-DLAs and 3 DLAS at z abs < 1.5 using the 6.5m Magellan II telescope with the MIKE spectrograph, and the 8.2m VLT-Kueyen telescope with the UVES spectrograph to study the properties of these systems and determine their metal content. We have measured the absorption lines of multiple lines in these systems and determined column densities and abundances. We have also created grids of photoionization models using CLOUDY to determine the effects of ionization in these systems. Although the gas is largely ionized, the abundances appear not to require significant ionization corrections. We find that the sub-DLAs, especially at low z are more metal rich than the DLA systems, with [Zn/H] subDLA = -0.30 ± 0.15 and [Zn/H] DLA = -0.94 ± 0.11. These systems appear to contain ~ 40 - 75% of the comoving mass density of metals that is seen in DLAs, [Special characters omitted.] ~ (4 - 11) × 10^-7 , dependent on the ionization. Kinematically, the sub-DLAs from this sample have larger velocity widths than the DLAs, perhaps implying that they arise in more massive galaxies with deeper potential wells. We also investigate the relative abundances of [Cr/Zn], [Fe/Zn], [Mn/Fe], and [Si/Fe] in these systems to study dust depletion and nucleosynthetic effects.

Meiring, Joseph D.

2008-06-01

123

Synergistic effect of ionizing radiation on chemical disinfectant treatments for reduction of natural microflora on seafood  

NASA Astrophysics Data System (ADS)

The purpose of this study was to determine whether combined treatments would produce synergistic disinfection effects on seafood products such as mussel and squid compared with single treatments. We investigated the bactericidal effects of chlorine and ionizing radiation on the natural microflora of mussel and squid. Total aerobic bacteria initially ranged from 102 to 104 Log CFU/g. More than 100 ppm of chlorine and irradiation at 1 kGy were sufficient to reduce the total aerobic bacteria on mussel and squid to a level lower than detection limit (10 CFU/g). Synergistic effects against natural microflora were observed for all combined treatment. These results suggest that a significant synergistic benefit results from combine chlorine-ionizing radiation treatment against natural microflora on mussel and squid.

Kim, Hyunjoo; Ha, Ji-Hyoung; Lee, Ju-Woon; Jo, Cheorun; Ha, Sang-Do

2012-08-01

124

Application of gas chromatography-hybrid chemical ionization mass spectrometry to the analysis of diclofenac in wastewater samples.  

PubMed

Hybrid chemical ionization (HCI), a new and useful alternative to conventional chemical ionization mass spectrometry, has been applied to the analysis of the pharmaceutical diclofenac in wastewater samples. This technique takes advantage of the high versatility of ion trap (IT) spectrometers combined with external ionization sources. In hybrid configuration, reagent ions are generated in the external source through electron ionisation (EI) of a reagent gas. These reagent ions are then drawn into the ion trap and only those selected are allowed to react with analytes eluting from the GC column. These ion-molecule reactions create analyte ions which are held in the ion trap. In this study ion-molecule reactions between C(3)F(5)(+) cations, generated from perfluorotributylamine (FC43), and diclofenac molecules have been investigated. The observed reaction products were [M+C(3)F(5)-H(2)O](+) adduct ions, which result from the initial electrophilic addition of C(3)F(5)(+) cations to the diclofenac molecule followed by the rapid loss of H(2)O. Further fragmentation of these ions by MS/MS yielded enough daughter ions for a reliable identification of diclofenac in complex matrices. The GC-HCI-MS/MS method applied to wastewater samples provided highly enhanced selectivity and sensibility, with a detection limit in real samples of 3.0 ng/L, for a solid-phase extraction (SPE) pre-concentration factor of 400. Other performance characteristics of the method, such as linearity and precision were also satisfactory. Finally, the method was successfully applied to the analysis of wastewater samples taken from the effluent of an urban sewage treatment plant (STP). PMID:16956617

Agüera, A; Mezcua, M; Mocholí, F; Vargas-Berenguel, A; Fernández-Alba, A R

2006-11-10

125

Determination of nitrosamines in water by gas chromatography/chemical ionization/selective ion trapping mass spectrometry.  

PubMed

A gas chromatography/mass spectrometry (GC/MS) method for determination of nine N-nitrosamines (NAs) in water is described. Two ionization modes, electron impact (EI) and chemical ionization (CI) with methanol, as well as different ion analysis techniques, i.e. full scan, selected ion storage (SIS) and tandem mass spectrometry (MS/MS) were tested. Chemical ionization followed by SIS resulted the mass spectrometric method of choice, with detection limits in the range of 1-2ng/L. Solid Phase Extraction (SPE) with coconut charcoal cartridges was applied to extract NAs from real samples, according EPA Method 521. Drinking water samples were collected from seven surface- and two groundwater treatment plants. Three surface water treatment plants were sampled before and after addition of O(3)/ClO(2) to observe the effect of disinfection on NAs' formation. N-nitrosodiethylamine (NDEA), n-nitrosodipropylamine (NDPA), n-nitrosomorpholine (NMOR) and n-nitrosodibutylamine (NDBA) were found up to concentrations exceeding three times the risk level of 10ng/L set by the California Department of Public Health. Because dermal adsorption has been recently indicated as a new contamination route of exposure to NAs for people who practice swimming activity, water samples from five swimming pools in the Bologna (Italy) area were collected. N-nitrosopyrrolidine (NPYR) was detected in all samples at concentrations larger than 50ng/L, likely as a disinfection by-product from the amino acid precursor proline, a main constituent of skin collagen. PMID:21377686

Pozzi, Romina; Bocchini, Paola; Pinelli, Francesca; Galletti, Guido C

2011-04-01

126

A sensitive negative-ion electrospray ionization mass spectrometry detection for metallothionein in tris(hydroxymethyl)aminomethane acetate buffer  

NASA Astrophysics Data System (ADS)

Although positive-ion (PI) electrospray ionisation mass spectrometry (ESI-MS) has been usually applied for the analysis of native metallothioneins (MT) isoforms binding with metal ions, it suffers from the lack of insensitivity under neural conditions because of the low efficiency of protonation during ESI process. In this study, multiply deprotonated metallothionein (Zn7-MT-2a), produced from tris(hydroxymethyl)aminomethane (TRIS) acetate solutions under near neutral condition, was analyzed by negative-ion (NI) ESI-MS. Compared with the ammonium acetate buffer system which has been normally used for ESI-MS experiments, the use of TRIS acetate buffer results in the formation of more abundant ions and higher charge states of MT-2a, and consequently higher intensity is attained. The sensitivity enhancement of the system could be explained by the high gas-phase proton affinity, small molecular volume of the anion (acetate), and the high hydrogen consumption by TRIS in the buffer system, which would all favor the deprotonation of the analyte during NI-ESI process. Factors that may affect the NI-ESI responses, such as acid added in buffer, pH and concentration of TRIS acetate had been evaluated, and the result showed that using acetic acid, lower pH under the pH range evaluated, higher concentration of TRIS acetate all favored the MS detection of MT-2a. Our finding sheds light on a buffer system that may offer substantial sensitivity advantages in the studying of weakly bound, non-covalent complexes such as metal binding MTs, which are usually analyzed under near neutral conditions.

Shen, Jin-Can; Lu, Su-Ge; Zhuang, Zhi-Xia; Wang, Xiao-Ru; Lee, Frank S. C.

2005-05-01

127

ChemicalPhysicsLetters240(1995)278-282 Time evolution and multiphoton ionization of Rydberg  

E-print Network

ELSEVIER 30June1995 ChemicalPhysicsLetters240(1995)278-282 CHEMICAL PHYSICS LETTERS Time evolution of Physics, National Chiao-Tung University, Hsinehu, Taiwan, ROC bDepartment of Chemistry, University a theoretical study of the time evolution of Rydberg wavepacket, initially localized in radial space

Chu, Shih-I

128

Investigating the Chemical Evolution of the Universe via Numerical Simulations: Supernova Dust Destruction and Non-Equilibrium Ionization Chemistry  

NASA Astrophysics Data System (ADS)

The chemical evolution of the Universe is a complicated process with countless facets that define its properties over the course of time. In the early Universe, the metal-free first stars were responsible for originally introducing metals into the pristine gas left over from the Big Bang. Once these metals became prevalent, they forever altered the thermodynamics of the Universe. Understanding precisely where these metals originated, where they end up, and the conditions they experience along the way is of great interest in the astrophysical community. In this work, I have used numerical simulations as a means of understanding two separate phenomena related to the chemical evolution the Universe. The first topic focuses on the question as to whether or not core-collapse supernovae in the high-redshift universe are capable of being "dust factories" for the production of galactic dust. To achieve this, I carried out idealized simulations of supernova ejecta clouds being impacted by reverse-shock blast waves. By post-processing the results of these simulations, I was able to estimate the amount of dust destruction that would occur due to thermal sputtering. In the most extreme scenarios, simulated with high relative velocities between the shock and the ejecta cloud and high gas metallicities, I find complete destruction for some grains species and only 44% dust mass survival for even the most robust species. This raises the question as to whether or not high-redshift supernova can produce dust masses in sufficient excess of the ˜1 Msun per event required to match observations of high-z galaxies. The second investigation was driven by the desire to find an answer to the missing baryon problem and a curiosity as to the impact that including a full non-equilibrium treatment of ionization chemistry has on simulations of the intergalactic medium. To address these questions, I have helped to develop Dengo, a new software package for solving complex chemical networks. Once this new package was integrated into Enzo, I carried out a set of cosmological simulations that served as both a test of the new solver and a confirmation that non-equilibrium ionization chemistry produces results that are drastically different from those that assume collisional ionization equilibrium. Although my analysis of these simulations is in its early stages, I find that the observable properties of the intergalactic medium change considerably. Continued efforts to run state-of-the-art simulations of the intergalactic medium using Dengo are warranted.

Silvia, Devin W.

129

High-resolution chemical ionization mass spectrometry (ToF-CIMS): application to study SOA composition and processing  

NASA Astrophysics Data System (ADS)

This paper demonstrates the capabilities of chemical ionization mass spectrometry (CIMS) to study secondary organic aerosol (SOA) composition with a high-resolution (HR) time-of-flight mass analyzer (aerosol-ToF-CIMS). In particular, by studying aqueous oxidation of water-soluble organic compounds (WSOC) extracted from ?-pinene ozonolysis SOA, we assess the capabilities of three common CIMS reagent ions: (a) protonated water clusters (H2O)nH+, (b) acetate CH3C(O)O- and (c) iodide water clusters I(H2O)n- to monitor SOA composition. Furthermore, we report the relative sensitivity of these reagent ions to a wide range of common organic aerosol constituents. We find that (H2O)nH+ is more selective to the detection of less oxidized species, so that the range of O / C and OSC (carbon oxidation state) in the SOA spectra is considerably lower than those measured using CH3C(O)O- and I(H2O)n-. Specifically, (H2O)nH+ ionizes organic compounds with OSC ? 1.3, whereas CH3C(O)O- and I(H2O)n- both ionize highly oxygenated organics with OSC up to 4 with I(H2O)n- being more selective towards multi-functional organic compounds. In the bulk O / C and H / C space (in a Van Krevelen plot), there is a remarkable agreement in both absolute magnitude and oxidation trajectory between ToF-CIMS data and those from a high-resolution aerosol mass spectrometer (HR-AMS). Despite not using a sensitivity-weighted response for the ToF-CIMS data, the CIMS approach appears to capture much of the chemical change occurring. As demonstrated by the calibration experiments with standards, this is likely because there is not a large variability in sensitivities from one highly oxygenated species to another, particularly for the CH3C(O)O- and I(H2O)n- reagent ions. Finally, the data illustrate the capability of aerosol-ToF-CIMS to monitor specific chemical change, including the fragmentation and functionalization reactions that occur during organic oxidation, and the oxidative conversion of dimeric SOA species into monomers. Overall, aerosol-ToF-CIMS is a valuable, selective complement to some common SOA characterization methods, such as AMS and spectroscopic techniques. Both laboratory and ambient SOA samples can be analyzed using the techniques illustrated in the paper.

Aljawhary, D.; Lee, A. K. Y.; Abbatt, J. P. D.

2013-11-01

130

Mapping the response of a chemically amplified negative photoresist for x-ray lithography  

NASA Astrophysics Data System (ADS)

A variety of techniques have been developed to assess the performance and mechanism of image formation in chemically-amplified resists. The system chosen for this study was the negative tone, SAL 605 from the Shipley Co., under exposure to 1 nm X-rays. This resist system utilizes a novolac resin, the crosslinker molecule hexamethoxymethylmelamine (HMMM), and a photoacid acid generator (PAG). Under exposure to X-rays, the amount of acid generated within the film was approximately 5 × 10sp{-06} moles/cmsp3 under conditions sufficient to print 0.215 mum lines, and was found to catalyze approximately 26 reactions during the post-exposure bake. Only 1.27 reactions per HMMM molecule occur, about 2% of the phenolic entities are protected, and the resist does not crosslink. The molar absorptivity of the ether peak corresponding to the reaction between the HMMM and novolac was measured within the matrix of the film to be 3.1 × 10sp{05} cmsp2/mol. Using real-time FTIR, a full kinetic model was proposed for this system, with all measurements made within the matrix of the film. At lithographic temperatures, the reaction proceeded until approximately one reaction had occurred on all of the HMMM and then slowed down for subsequent reactions on the remaining available sites on the HMMM molecules. A technique to measure the acid distribution within the photoresist film was developed, using a pH-dependent fluorescent molecule included within the film and detected with high spatial-resolution optical microscopy, in collaboration with Yale University. The reactive ion etch resistance of polymer films utilized in lithography with the inclusion of Csb{60} Fullerene additives, was studied. Csb{60} molecules are shown to be more etch resistant than other common additives. A photoresist adhesion monitoring technique, indentation debonding, was utilized to study the response of PMMA to silicon wafers treated with different surface treatments. The application of silane coupling agents markedly affected the mechanical adhesion, with potential to simultaneously improve lithographic adhesion.

Dentinger, Paul M.

131

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

with greater than 1% relative abundance in either phase are shown. Pyrolysis of solid biomass, in this case: Characterization of Pine Pellet and Peanut Hull Pyrolysis of Bio-Oils by Negative-Ion Electrospray Ionization of nitrogen-containing species identified in the peanut hull pyrolysis oil by FT-ICR mass spectrometry

Weston, Ken

132

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

133

Accurate quantitation of pentaerythritol tetranitrate and its degradation products using liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.  

PubMed

After an explosion of pentaerythritol tetranitrate (PETN), its degradation products pentaerythritol trinitrate (PETriN), dinitrate (PEDiN) and mononitrate (PEMN) were detected using liquid chromatography-atmospheric-pressure chemical-ionization-mass spectrometry (LC-APCI-MS). Discrimination between post-explosion and naturally degraded PETN could be achieved based on the relative amounts of the degradation products. This information can be used as evidence when investigating a possible relationship between a suspect and a post-explosion crime scene. The present work focuses on accurate quantitation of PETN and its degradation products, using PETriN, PEDiN and PEMN standards specifically synthesized for this purpose. With the use of these standards, the ionization behavior of these compounds was studied, and a quantitative method was developed. Quantitation of PETN and trace levels of its degradation products was shown to be possible with accuracy between 85.7% and 103.7% and a precision ranging from 1.3% to 11.5%. The custom-made standards resulted in a more robust and reliable method to discriminate between post-explosion and naturally-degraded PETN. PMID:24656542

Brust, Hanneke; van Asten, Arian; Koeberg, Mattijs; Dalmolen, Jan; van der Heijden, Antoine; Schoenmakers, Peter

2014-04-18

134

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

135

Direct monitoring of chemical transformations by combining thin layer chromatography with nanoparticle-assisted laser desorption/ionization mass spectrometry.  

PubMed

A nanomaterial-assisted method that combines thin layer chromatography (TLC) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) was developed to directly monitor chemical transformations. A substrate-dependent extraction strategy was studied and successfully used to identify target molecules from the depths of a developed TLC plate. By using this strategy, a hydrophobic sample of interest was enriched on the surface of the TLC plate in the presence of acetonitrile, in contrast to using water and methanol to identify hydrophilic samples. The successful enrichment of samples by specific solvents provided stable desorption/ionization efficiencies of compounds of interest and led to very good sensitivity near the attomole scale. The method was then used to monitor 4-dimethylaminopyridine (DMAP)-catalyzed acylation in preparation of bifunctional sulfonamides. The labile DMAP-acyl intermediate and final sulfonamide product were clearly identified on TLC plates without external purification or sample preparation. Furthermore, in combination with collision-induced dissociation (CID) to provide structural information, the technique was successfully used in the natural product discovery of anti-inflammatory flavonoids from Helminthostachys zeylanica, a traditional Chinese herb. The newly proposed method provides a very low background from silica supports or organic matrices in the low molecular weight range (100-1000 Da). The technique may greatly accelerate studies of metabolomics, drug discovery, and organic synthesis. PMID:23330148

Chen, Chun-Chi; Yang, Yung-Lin; Ou, Chun-Lin; Chou, Chih-Hung; Liaw, Chih-Chuang; Lin, Po-Chiao

2013-03-01

136

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

137

Observations of formic and acetic acid by chemical ionization mass spectrometry in the Deep Convective Clouds and Chemistry Experiment  

NASA Astrophysics Data System (ADS)

Formic (HFo) and acetic acid (HAc) are part of the atmospheric processing of carbon and their measurement is relevant to defining oxygenated volatile organic carbon (OVOC) emissions, to examining photochemical processing of volatile organic carbon (VOC) and OVOCs, and to the photochemical processing of organic aerosol. Further, they can serve as photochemical tracers of convective transport, cloud chemical processes, and precipitation scavenging. The addition of HFo and HAc measurements to the Deep Convective Clouds and Chemistry Experiment (DC3) is relevant to the DC3 science objectives and complements the suite of chemicals already observed during DC3. The peroxide chemical ionization mass spectrometer (PCIMS) was flown aboard the NCAR Gulfstream-V platform in DC3 and while its primary function was to observe hydrogen peroxide and methylhydroperoxide it recorded signals attributed to iodide cluster ions of HFo and HAc at mass-charge ratios of 173 and 187, respectively. Post-mission laboratory experiments were performed to determine the CIMS instrument's sensitivity to these acids under the varying water vapor and sample flow conditions encountered during DC3 flights. The results of field measurements, laboratory experiments and the HFo and HAc recovery process are reported and HFo and HAc measurement quality assessed. The resultant HFo and HAc data are presented and interpreted with respect to atmospheric chemistry within measurement constraints. The DC3 observations were made in May and June 2012 and extended from the surface to 13 km over the central United States.

Treadaway, V.; McNeill, A.; Heikes, B.; O'Sullivan, D. W.; Silwal, I.

2013-12-01

138

Investigation of the Reactivity of Oligodeoxynucleotides with Glyoxal and KMnO4 Chemical Probes by Electrospray Ionization Mass Spectrometry  

PubMed Central

The reactions of two well-known chemical probes, glyoxal and potassium permanganate (KMnO4), with oligodeoxynucleotides were monitored by electrospray ionization (ESI) mass spectrometry to evaluate the influence of the sequence of DNA, its secondary structure, and interactions with associated ligands on the reactivity of the two probes. Glyoxal, a guanine-reactive probe, incorporated a mass shift of 58 Da, and potassium permanganate (KMnO4) is a thymine-reactive probe that resulted in a mass shift of 34 Da. The reactions depended on the accessibility of the nucleobases, and the peak abundances of the adducts in the ESI-mass spectra were used to quantify the extent of the chemical probe reactions. In this study, both mixed-base sequences were studied as well as control sequences in which one reactive site was located at the terminus or center of the oligodeoxynucleotide while the surrounding bases were a second, different nucleobase. In addition, the reactions of the chemical probes with non-covalent complexes formed between DNA and either actinomycin D or ethidium bromide, both known to interact with single strand DNA, were evaluated. PMID:21743793

Parr, Carol; Pierce, Sarah E.; Smith, Suncerae I.; Brodbelt, Jennifer S.

2010-01-01

139

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

140

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

141

Measurements of hydroxyl radical reactivity using a chemical ionization mass spectrometry technique  

Microsoft Academic Search

Typically tropospheric chemical models overestimate [OH] when compared to measurements. This discrepancy is usually attributed to incompletely modeling OH sinks due to a lack of measurements. The determination of OH reactivity provides an independent means to quantify the overall contribution of these unmeasured trace species to OH oxidation. Therefore, a new instrument was developed to measure the total loss rate

Joshua Aaron McGrath

2010-01-01

142

Experts Workshop on the Ecotoxicological Risk Assessment of Ionizable Organic Chemicals: Bioaccumulation/ADME  

EPA Science Inventory

The bioaccumulation potential of neutral organic chemicals (e.g., PCBs, DDT, brominated flame retardants) has received a great deal of attention from scientists in the field of environment toxicology and chemistry over the past four decades. Regulations based on our understanding...

143

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

144

Use of electron ionization and atmospheric pressure chemical ionization in gas chromatography coupled to time-of-flight mass spectrometry for screening and identification of organic pollutants in waters.  

PubMed

A new approach has been developed for multiclass screening of organic contaminants in water based on the use of gas chromatography coupled to hybrid quadrupole high-resolution time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI)QTOF MS). The soft ionization promoted by the APCI source allows effective and wide-scope screening based on the investigation of the molecular ion and/or protonated molecule. This is in contrast to electron ionization (EI) where ionization typically results in extensive fragmentation, and diagnostic ions and/or spectra need to be known a priori to facilitate detection of the analytes in the raw data. Around 170 organic contaminants from different chemical families were initially investigated by both approaches, i.e. GC-(EI)TOF and GC-(APCI)QTOF, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and a notable number of pesticides and relevant metabolites. The new GC-(APCI)QTOF MS approach easily allowed widening the number of compounds investigated (85 additional compounds), with more pesticides, personal care products (UV filters, musks), polychloronaphthalenes (PCNs), antimicrobials, insect repellents, etc., most of them considered as emerging contaminants. Both GC-(EI)TOF and GC-(APCI)QTOF methodologies have been applied, evaluating their potential for a wide-scope screening in the environmental field. PMID:24674644

Portolés, Tania; Mol, Johannes G J; Sancho, Juan V; Hernández, Félix

2014-04-25

145

Analysis of chemical degradation mechanism within sky blue phosphorescent organic light emitting diodes by laser-desorption\\/ionization time-of-flight mass spectrometry  

Microsoft Academic Search

We present an investigation of the intrinsic chemical degradation mechanisms of phosphorescent OLEDs based on the common sky blue emitter bis(2-(4,6-difluorophenyl)pyridyl-N,C2?)iridium(III)picolinate (FIrpic). The OLEDs are investigated using the laser-desorption\\/ionization time-of-flight mass spectrometry. The comparison between the collected spectra for electrically aged and unaged OLEDs allows the identification of different reaction products, like fragments which are mainly related to the chemical

Ines Rabelo de Moraes; Sebastian Scholz; Björn Lüssem; Karl Leo

2011-01-01

146

Identification of coagulase-negative staphylococci from bovine intramammary infection by matrix-assisted laser desorption ionization-time of flight mass spectrometry.  

PubMed

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

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

2014-05-01

147

Pulsed large volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry for simultaneous determination of typical halogenated persistent organic pollutants.  

PubMed

A pulsed large-volume injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry (pLVI-GC/ECNI-qMS) was developed for the simultaneous determination of typical halogenated persistent organic pollutants (H-POPs). By monitoring the characteristic ions of large mass-to-charge ratio (m/z) for each of the H-POPs rather than the chlorine and/or bromine ions, this method avoided the possible interferences arising from the H-POPs themselves and from complex matrices encountered frequently in current GC/qMS methods; and allowed, on the other hand, the use of (13)C-labeled and perdeuterated analogues as internal standards for reliable quantification. pLVI up to 120 microL improved the instrumental detection limits down to pg-fg mL(-1), comparable to or lower than those obtained by the recognized GC/high-resolution MS methods reported so far. The H-POPs including 12 polybrominated diphenyl ethers, 1 polybrominated biphenyl, 10 polychlorinated biphenyls (PCBs), 4 hexachlorocyclohexane isomers, and hexachlorobenzene were involved in this study. The method developed demonstrated good linearity (r(2) = 0.9904-0.9999) within 0.5 to 50,000 pg mL(-1) for PCBs and 0.05 to 5000 pg mL(-1) for other H-POPs, and was satisfactory in terms of both repeatability (0.07%-2.2%) and reproducibility (2.1%-8.4%). It was validated by analyzing a NIST standard reference material SRM-1946 of Lake Superior fish tissue with low 0.01 to 63 pg g(-1) method detection limits, and successfully applied to the determination of the H-POPs in five reference materials of different matrices. PMID:17533137

Zhao, Yuli; Yang, Limin; Wang, Qiuquan

2007-08-01

148

Chemical resistance of the gram-negative bacteria to different sanitizers in a water purification system  

Microsoft Academic Search

BACKGROUND: Purified water for pharmaceutical purposes must be free of microbial contamination and pyrogens. Even with the additional sanitary and disinfecting treatments applied to the system (sequential operational stages), Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas alcaligenes, Pseudomonas picketti, Flavobacterium aureum, Acinetobacter lowffi and Pseudomonas diminuta were isolated and identified from a thirteen-stage purification system. To evaluate the efficacy of the chemical

Priscila G Mazzola; Thereza CV Penna

2006-01-01

149

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  

Microsoft Academic Search

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

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

2008-01-01

150

Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation.  

PubMed

Mathematical analytical model of the processes running in individual radical clusters during the chemical phase (under the presence of radiomodifiers) proposed by us earlier has been further developed and improved. It has been applied to the data presented by Blok and Loman characterizing the oxygen effect in SSB and DSB formation (in water solution and at low-LET radiation) also in the region of very small oxygen concentrations, which cannot be studied with the help of experiments done with living cells. In this new analysis the values of all reaction rates and diffusion parameters known from literature have been made use of. The great increase of SSB and DSB at zero oxygen concentration may follow from the fact that at small oxygen concentrations the oxygen absorbs other radicals while at higher concentrations the formation of oxygen radicals prevails. It explains the double oxygen effect found already earlier by Ewing. The model may be easily extended to include also the effects of other radiomodifiers present in medium during irradiation. PMID:23307067

Barilla, Ji?í; Lokají?ek, Miloš; Pisaková, Hana; Simr, Pavel

2013-03-01

151

Analysis of malachite green and metabolites in fish using liquid chromatography atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Malachite green (MG), a traditional agent used in aquaculture, is structurally related to other carcinogenic triphenylmethane dyes. Although MG is not approved for use in aquaculture, its low cost and high efficacy make illicit use likely. We developed sensitive and specific methods for determination of MG and its principal metabolite, leucoMG (LMG), in edible fish tissues using isotope dilution liquid chromatography atmosphere pressure chemical ionization mass spectrometry. MG and LMG concentrations were measured in filets from catfish treated with MG under putative use conditions (ca. 250 and 1000 ppb, respectively) and from commercial trout samples (0-3 and 0-96 ppb, respectively). Concentrations of LMG in edible fish tissues always exceeded those of MG. A rapid cone voltage switching acquisition procedure was used to simultaneously produce molecular ions for quantification and diagnostic fragment ions for confirmation of MG and metabolites. The accurate and precise agreement between diagnostic ion intensity ratios produced by LMG in authentic standards and incurred fish samples was used to unambiguously confirm the presence of LMG in edible fish tissue. This suggested the validity of using LMG as a marker residue for regulatory determination of MG misuse. Additional metabolites derived from oxidative metabolism of MG or LMG (demethylation and N-oxygenation) were identified in catfish and trout filets, including a primary arylamine which is structurally related to known carcinogens. The ability to simultaneously quantify residues of MG and LMG, and to confirm the chemical structure of a marker residue by using LC/MS, suggests that this procedure may be useful in monitoring the food supply for the unauthorized use of MG in aquaculture. PMID:9807836

Doerge, D R; Churchwell, M I; Gehring, T A; Pu, Y M; Plakas, S M

1998-01-01

152

Determination and characterization of organic explosives using porous graphitic carbon and liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

A new LC-MS method for the determination and characterization of three groups of commonly used organic explosives (nitroaromatic compounds, cyclic nitroamines and nitrate esters) was developed using a porous graphitic carbon (PGC) (Hypercarb) column. Twenty-one different explosive-related compounds--including 2,4,6-trinitrotoluene, its by-products and its degradation products--were chromatographically separated in a single analysis. This efficient separation facilitates the identification of the manufacturer of the explosive using the identified analytes as a fingerprint. A final, conclusive identification of the analytes can be obtained using LC-MS equipped with an atmospheric pressure chemical ionization (APCI) interface. Solvent effects on chromatographic behaviour were investigated, as were the effects of solvent mixtures and mobile phase additives. The number and the relative positions of the nitro groups within analyte molecules influence their order of elution; these effects were investigated. The data thus generated can be interpreted to support a hypothesis concerning the retention mechanism of nitro-containing compounds when using PGC. Limits of detection ranged from 0.5 to 41.2 ng. The new methodology described herein improves the sensitivity and selectivity of explosive detection. The effectiveness of the method is demonstrated by the analysis of soil samples containing explosives residue from test fields in Sweden and Afghanistan. PMID:16213509

Holmgren, Erik; Carlsson, Håkan; Goede, Patrick; Crescenzi, Carlo

2005-12-16

153

Thermal desorption counter-flow introduction atmospheric pressure chemical ionization for direct mass spectrometry of ecstasy tablets.  

PubMed

A novel approach to the analysis of ecstasy tablets by direct mass spectrometry coupled with thermal desorption (TD) and counter-flow introduction atmospheric pressure chemical ionization (CFI-APCI) is described. Analytes were thermally desorbed with a metal block heater and introduced to a CFI-APCI source with ambient air by a diaphragm pump. Water in the air was sufficient to act as the reactive reagent responsible for the generation of ions in the positive corona discharge. TD-CFI-APCI required neither a nebulizing gas nor solvent flow and the accompanying laborious optimizations. Ions generated were sent in the direction opposite to the air flow by an electric field and introduced into an ion trap mass spectrometer. The major ions corresponding to the protonated molecules ([M + H](+)) were observed with several fragment ions in full scan mass spectrometry (MS) mode. Collision-induced dissociation of protonated molecules gave characteristic product-ion mass spectra and provided identification of the analytes within 5 s. The method required neither sample pretreatment nor a chromatographic separation step. The effectiveness of the combination of TD and CFI-APCI was demonstrated by application to the direct mass spectrometric analysis of ecstasy tablets and legal pharmaceutical products. PMID:19565470

Inoue, Hiroyuki; Hashimoto, Hiroaki; Watanabe, Susumu; Iwata, Yuko T; Kanamori, Tatsuyuki; Miyaguchi, Hajime; Tsujikawa, Kenji; Kuwayama, Kenji; Tachi, Noriyuki; Uetake, Naohito

2009-09-01

154

Analyses of polycyclic aromatic hydrocarbons in seafood by capillary electrochromatography-atmospheric pressure chemical ionization/mass spectrometry.  

PubMed

In this work, an on-line preconcentration capillary electrochromatographic (CEC) separation coupled with atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) was used for 16 PAHs analyses, in which poly(stearyl methacrylate-divinylbenzene) (poly(SMA-DVB)) monolith was used as the separation column. With variations in the effective length of poly(SMA-DVB) monolith as well as the volume fraction of acetonitrile (ACN) in the mobile phase, both separation and resolution were improved. A poly(SMA-DVB) monolith of 50-cm effective length (i.e. 50-cm column length filled with polymer) and a two-step step-gradient elution (by changing the ACN levels of the mobile phase starting with an initial of 70% up to 80% with 30-min time interval), which provided baseline separation for PAHs solutes (except for chrysene and benzo[a]anthracene) within 50 min, were employed as the optimal chromatographic conditions. In contrast to the other mass spectrometer parameters (nebulizer gas pressure, vaporizer temperature, corona current) as well as on-line preconcentration parameter (the ACN level in the sample matrix), the sheath liquid composition (methanol/water in the ratio of 3:1) and the sample injection time (40 min) were found as the predominant factors that control the sensitivity of PAHs determination. Finally, this on-line preconcentration CEC-APCI-MS method determined PAH residues in seafood samples successfully with as low as 10 ng/g level. PMID:23992841

Cheng, Yi-Jie; Huang, Sing-Hao; Chiu, Ju-Yin; Liu, Wan-Ling; Huang, Hsi-Ya

2013-10-25

155

[Determination of naphthenic acids in distillates of crude oil by gas chromatography/chemical ionization-mass spectrometry].  

PubMed

The petroleum carboxylic acids in 200-420 degrees C distillate of crude oil were separated by the extraction with column chromatography on an anion exchange resin. The effect of the composition and structure of naphthenic acids on separation were studied by the infra-red (IR) spectroscopic techniques. Naphthenic acids and iso-butane reagent gas were introduced into the ion source for chemical ionization, in which the ions represented by [M + C4H9]+ were used to calculate the relative molecular mass for each acid. Based on the mass spectra of pure fatty and naphthenic acids, in combination with the z-series formula CnH(2n + z)O2, the naphthenic acids can be classified into fatty, mono-, bi- ... hexa-cyclic types. The results indicated that the relative molecular mass range of naphthenic acids in this distillates was 170-510, and the carbon number range was C10-C35. The contents of bi-cyclic and tri-cyclic naphthenic acids were higher than others. PMID:15712901

Lü, Zhenbo; Tian, Songbai; Zhai, Yuchun; Sun, Yanwei; Zhuang, Lihong

2004-05-01

156

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

157

Chemically amplified negative-tone photoresist for sub-half-micron device and mask fabrication  

NASA Astrophysics Data System (ADS)

In this paper we discuss a new alkaline soluble negative acting photoresist which incorporates a phenolic based resin, urea/formaldehyde prepolymer as a crosslinking agent and an organic acid-generating sensitizer. This system, dubbed 'EBX' (Electron Beam/X-ray) resist has demonstrated excellent lithographic properties in various exposure modes. Discussion will center on imaging characteristics in the deep and mid ultraviolet using Micrascan I and I-line (365 nm) steppers; electron-beam imaging with MEBES 10 kV mask maker and IBM's EL-4 50 kV electron beam exposure system; and XRAY imaging with point source soft x-ray and synchotron hard x-ray lithography.

Conley, Will; Dundatscheck, Robert; Gelorme, Jeffrey D.; Horvat, John; Martino, Ronald M.; Murphy, Elizabeth; Petrosky, Anne; Spinillo, Gary T.; Stewart, Kevin J.; Wilbarg, Robert; Wood, Robert L.

1991-06-01

158

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

159

Negative thermal ion mass spectrometry of osmium, rhenium, and iridium  

NASA Technical Reports Server (NTRS)

This paper describes a technique for obtaining, in a conventional surface ionization mass spectrometer, intense ion beams of negatively charged oxides of Os, Re, and Ir by thermal ionization. It is shown that the principal ion species of these ions are OsO3(-), ReO4(-), and IrO2(-), respectively. For Re-187/Os-187 studies, this technique offers the advantage of isotopic analyses without prior chemical separation of Re from Os.

Creaser, R. A.; Papanastassiou, D. A.; Wasserburg, G. J.

1991-01-01

160

Chemically modified oligonucleotide-increased stability negatively correlates with its efficacy despite efficient electrotransfer.  

PubMed

Despite great potential for disease treatment, small interfering RNA (siRNA) development has been hampered due to its poor stability and the lack of efficient delivery method. To overcome the sensitivity, new generations of chemically modified oligonucleotides have been developed such as the locked nucleic acid (LNA). LNA substitution in an siRNA sequence (siLNA) is supposed to increase its stability and its affinity for its complementary sequence. The purpose of this study was to evaluate the potential benefit of an anti-GFP siLNA using the biophysical delivery method electropermeabilization. We used two types of electrical conditions: electrochemotherapy (ECT), a condition for efficient transfer of small molecules in clinics, and electrogenotherapy (EGT), a condition for efficient transfer of macromolecules. We first confirmed that siLNA was indeed more stable in mouse serum than unmodified siRNA. After determining the ECT and EGT optimal electrical parameters for a human colorectal carcinoma cell line (HCT-116) expressing eGFP, we showed that modifications of siRNA do not interfere with electrotransfer efficiency. However, despite its higher stability and its high electrotransfer efficacy, siLNA was less efficient for eGFP silencing compared to the electrotransferred, unmodified siRNA regardless of the electrical conditions used. Our study highlighted the care that is needed when designing chemically modified oligonucleotides. PMID:22797942

Pelofy, Sandrine; Teissié, Justin; Golzio, Muriel; Chabot, Sophie

2012-09-01

161

Sequential solid phase extraction protocol followed by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry for the trace determination of non ionic polyethoxylated surfactants in tannery wastewaters  

SciTech Connect

Automated solid-phase extraction (SPE) with C18 and styrene-divinylbenzene cartridges in series was used for the preconcentration of non ionic polyethoxylated surfactants in tannery wastewater. Fractionated extracts were analyzed by LC-MS using Atmospheric Pressure Chemical Ionization (APCI) in the Positive and Negative Ion modes. Recoveries for nonionic surfactants were approximately of 72, 90 and 80% for polyethylene glycols, nonylphenol and alcohol ethoxylates in the polar, aromatic and medium polarity fractions, respectively. Data acquisition in the selected ion monitoring mode afforded limits of quantification from 0.1 to 0.8 {micro}g/l for tridecylic polyethoxylated alcohol and polyethoxylated glycol, respectively, in the complex tannery wastewaters. The tannery effluents investigated contained between 0.03 to 3.0 mg/l of polyethylene glycol and nonylphenol polyethoxylate, respectively.

Castillo, M.; Barcelo, D. [IIQAB-CSIC, Barcelona (Spain). Dept. of Environmental Chemistry] [IIQAB-CSIC, Barcelona (Spain). Dept. of Environmental Chemistry; Ventura, F. [AGBAR, Barcelona (Spain)] [AGBAR, Barcelona (Spain)

1999-06-01

162

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

E-print Network

containing nylons and Kevlar. The effect of ionizing radiation (UV, x-rays, gamma rays, cosmic rays by ionizing radiation Phillip S. Johnson,1 Peter L. Cook,1 Xiaosong Liu,2 Wanli Yang,2 Yiqun Bai,3 Nicholas L, electrons) on biomolecules and polymers2 has been of great interest for many reasons. Examples are radiation

Himpsel, Franz J.

163

Determination of eight nitrosamines in water at the ng L ?1 levels by liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry  

Microsoft Academic Search

In this work, we have developed a sensitive method for detection and quantification of eight N-nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMor), N-nitrosomethylethylamine (NMEA), N-nitrosopirrolidine (NPyr), N-nitrosodiethylamine (NDEA), N-nitrosopiperidine (NPip), N-nitroso-n-dipropylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) in drinking water. The method is based on liquid chromatography coupled to tandem mass spectrometry, using atmospheric pressure chemical ionization (APCI) in positive mode with a triple

Cristina Ripollés; Elena Pitarch; Juan V. Sancho; Francisco J. López; Félix Hernández

2011-01-01

164

Determination of talinolol in human plasma using automated on-line solid phase extraction combined with atmospheric pressure chemical ionization tandem mass spectrometry  

Microsoft Academic Search

A specific LC–MS\\/MS assay was developed for the automated determination of talinolol in human plasma, using on-line solid phase extraction system (prospekt 2) combined with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry. The method involved simple precipitation of plasma proteins with perchloric acid (contained propranolol) as the internal standard (IS) and injection of the supernatant onto a C8 End

Emmanuel Bourgogne; Chantal Grivet; Gérard Hopfgartner

2005-01-01

165

Development of a method for quantitation of retinol and retinyl palmitate in human serum using high-performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry  

Microsoft Academic Search

A method for the quantitative analysis of the vitamin A compounds all-trans-retinol and all-trans-retinyl palmitate was developed using high-performance liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry (APCI–LC–MS). Unlike previous quantitative mass spectrometric methods for vitamin A, HPLC separations were carried out using a C30 reversed-phase column instead of GC separation. Because no sample hydrolysis or derivatization was necessary, retinyl palmitate was

Richard B van Breemen; Dejan Nikolic; Xiaoying Xu; Yansan Xiong; Machteld van Lieshout; Clive E West; Alexander B Schilling

1998-01-01

166

A novel method for analyzing solanesyl esters in tobacco leaves using atmospheric pressure chemical ionization/mass spectrometer.  

PubMed

A direct and simple method for analyzing solanesyl esters found in tobacco leaves was developed. Sample preparation was performed by accelerated solvent extractor 200 (ASE200) using n-hexane followed by evaporating solution in vacuo and dissolving residue with acetone. The separation of analytes was conducted through high-performance liquid chromatography (HPLC) equipped with an SIL-C18/5C column and the non-aqueous reversed phase chromatography (NARP) technique using acetone and acetonitrile as the mobile phase with a linear gradient. Atmospheric pressure chemical ionization/mass spectrometer (APCI/MS) in positive mode was used to detect solanesyl esters in the following conditions: capillary voltage 4000 V, corona current 10 microA, drying gas flow 5 mL/min, fragmentor voltage 200 V, nebulizer pressure 60 psi, and vaporizer temperature 500 degrees C. Each solanesyl ester was identified by the comparison of analyte with synthesized solanesyl esters. Quantification was conducted by selected ion monitoring (SIM) mode in order to detect the specific product ion (613.6 m/z) fragmented from solanesyl ester. The calibration curve was made in the range of 0.1-40 microg/mL with a regression coefficient over 0.999 on almost all solanesyl esters. The limit of detection (LOD) and limit of quantification (LOQ) ranged from 0.01 to 0.05 microg/mL and from 0.03 to 0.15 microg/mL, respectively, on the SIM mode of MS for quantification. Recovery (%) ranged from about 80 to 120%. The direct quantification using the developed method succeeded in showing a different amount and composition of solanesyl esters among various tobacco leaves. PMID:20691974

Ishida, Naoyuki

2010-09-10

167

Total microcystins analysis in water using laser diode thermal desorption-atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

A new approach for the analysis of the cyanobacterial microcystins (MCs) in environmental water matrices has been developed. It offers a cost efficient alternative method for the fast quantification of total MCs using mass spectrometry. This approach permits the quantification of total MCs concentrations without requiring any derivatization or the use of a suite of MCs standards. The oxidation product 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) was formed through a Lemieux oxidation and represented the total concentration of free and bound MCs in water samples. MMPB was analyzed using laser diode thermal desorption-atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS). LDTD is a robust and reliable sample introduction method with ultra-fast analysis time (<15 s sample(-1)). Several oxidation and LDTD parameters were optimized to improve recoveries and signal intensity. MCs oxidation recovery yield was 103%, showing a complete reaction. Internal calibration with standard addition was achieved with the use of 4-phenylbutyric acid (4-PB) as internal standard and showed good linearity (R(2)>0.999). Limits of detection and quantification were 0.2 and 0.9 ?g L(-1), respectively. These values are comparable with the WHO (World Health Organization) guideline of 1 ?g L(-1) for total microcystin-LR congener in drinking water. Accuracy and interday/intraday variation coefficients were below 15%. Matrix effect was determined with a recovery of 91%, showing no significant signal suppression. This work demonstrates the use of the LDTD-APCI-MS/MS interface for the screening, detection and quantification of total MCs in complex environmental matrices. PMID:24745740

Roy-Lachapelle, Audrey; Fayad, Paul B; Sinotte, Marc; Deblois, Christian; Sauvé, Sébastien

2014-04-11

168

Array of Chemically Etched Fused Silica Emitters for Improving the Sensitivity and Quantitation of Electrospray Ionization Mass Spectrometry  

SciTech Connect

An array of emitters has been developed for increasing the sensitivity of electrospray ionization mass spectrometry (ESI-MS). The linear array consists of 19 chemically etched fused silica capillaries arranged with 500 µm (center-to-center) spacing. The multi-emitter device has a low dead volume to facilitate coupling to capillary liquid chromatography (LC) separations. The high aspect ratio of the emitters enables operation at flow rates as low as 20 nL/min/emitter, effectively extending the benefits of nanoelectrospray to higher flow rate analyses. To accommodate the larger ion current produced by the emitter array, a multi-capillary inlet to the mass spectrometer was also constructed. The inlet, which matched the dimensions of the emitter array, effectively preserved ion transmission efficiency. Standard reserpine solutions of varying concentration were electrosprayed at 1 µL/min using the multi-emitter/multi-inlet combination, and compared to a standard, single emitter configuration. A nine-fold sensitivity enhancement was observed for the multi-emitter relative to the single emitter. A bovine serum albumin tryptic digest was also analyzed and resulted in a sensitivity increase ranging from 2.4 to 12.3-fold for the detected tryptic peptides; the varying response was attributed to reduced ion suppression under the nano-ESI conditions afforded by the emitter array. An equimolar mixture of leucine enkephalin and maltopentaose was studied to verify that ion suppression is indeed reduced for the multi-ESI array relative to a single emitter over a range of flow rates.

Kelly, Ryan T.; Page, Jason S.; Tang, Keqi; Smith, Richard D.

2007-06-01

169

Cyclic organic peroxides identification and trace analysis by Raman microscopy and open-air chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

The persistent use of cyclic organic peroxides in explosive devices has increased the interest in study these compounds. Development of methodologies for the detection of triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) has become an urgent priority. However, differences in physical properties between cyclic organic peroxides make difficult the development of a general method for peroxide analysis and detection. Following this urgency, the first general technique for the analysis of any peroxide, regarding its structural differences is reported. Characterization and detection of TATP and HMTD was performed using an Open-Air Chemical Ionization High-Resolution Time-of-Flight Mass Spectrometer. The first spectrometric analysis for tetramethylene diperoxide dicarbamide (TMDD) and other nitrogen based peroxides using Raman Microscopy and Mass Spectrometry is reported. Analysis of cyclic peroxides by GC-MS was also conducted to compare results with OACI-HRTOF data. In the OACI mass spectrum, HMTD showed a clear signal at m/z 209 MH + and a small adduct peak at m/z 226 [M+NH4]+ that allowed its detection in commercial standard solutions and lab made standards. TMDD presented a molecular peak of m/z 237 MH+ and an adduct peak of m/z 254 [M+NH4]+. TATP showed a single peak at m/z 240 [M+NH4]+, while the peak of m/z 223 or 222 was completely absent. This evidence suggests that triperoxides are stabilized by the ammonium ion. TATP samples with deuterium enrichment were analyzed to compare results that could differentiate from HMTD. Raman microscopy was used as a complementary characterization method and was an essential tool for cyclic peroxides identification, particularly for those which could not be extensively purified. All samples were characterized by Raman spectroscopy to confirm the Mass Spectrometry results. Peroxide O-O vibrations were observed around 750-970 cm-1. D18-TATP studies had identified ketone triperoxide nu(O-O) vibration around 875 cm -1 in Raman. HMTD and TMDD shared nu(O-O) vibration around 912 cm -1(HMTD: 910 cm-1; TMDD: 914 cm-1). Some of the vibrations identified were nu(CH){3000-2930 cm-1}, delta(C-O){1000-1100 cm-1}, nu(CH-C){1470-1400 cm-1}, nu(N-C){1370 cm-1}, and nu(N-H){3340 cm-1}. Both Raman microscopy and OACI-mass spectrometry represent excellent alternatives to be used sensitive checkpoints and forensic laboratories.

Pena-Quevedo, Alvaro Javier

170

Chemical ionization mass spectrometric measurements of SO2 emissions from jet engines in flight and test chamber operations  

NASA Astrophysics Data System (ADS)

We report the results of two measurements of the concentrations and emission indices of gas-phase sulfur dioxide (EI(SO2)) in the exhaust of an F100-200E turbofan engine. The broad goals of both experiments were to obtain exhaust sulfur speciation and aerosol properties as a function of fuel sulfur content. In the first campaign, an instrumented NASA T-39 Sabreliner aircraft flew in close formation behind several F-16 fighter aircraft to obtain near-field plume composition and aerosol properties. In the second, an F-100 engine of the same type was installed in an altitude test chamber at NASA Glenn Research Center where gas composition and nonvolatile aerosol concentrations and size distributions were obtained at the exit plane of the engine. In both experiments, SO2 concentrations were measured with the Air Force Research Laboratory chemical ionization mass spectrometer as a function of altitude, engine power, and fuel sulfur content. A significant aspect of the program was the use of the same fuels, the same engine type, and many of the same diagnostics in both campaigns. Several different fuels were purchased specifically for these experiments, including high-sulfur Jet A (˜1150 ppmm S), low-sulfur Jet A (˜10 ppmm S), medium-sulfur mixtures of these two fuels, and military JP-8+100 (˜170 and ˜300 ppmm S). The agreement between the flight and test cell measurements of SO2 concentrations was excellent, showing an overall precision of better than ±10% and an estimated absolute accuracy of ±20%. The EI(SO2) varied from 2.49 g SO2/kg fuel for the high-sulfur fuel in the test chamber to less than 0.01 g/kg for the lowest-sulfur fuel. No dependence of emission index on engine power, altitude or simulated altitude, separation distance or plume age, or the presence of contrails was observed. In all experiments the measured EI(SO2) was consistent with essentially all of the fuel sulfur appearing as gas-phase SO2 in the exhaust. However, accurate determination of S(IV) to S(VI) conversion was hampered by inconsistencies in the assays of total fuel sulfur content.

Hunton, D. E.; Ballenthin, J. O.; Borghetti, J. F.; Federico, G. S.; Miller, T. M.; Thorn, W. F.; Viggiano, A. A.; Anderson, B. E.; Cofer, W. R.; McDougal, D. S.; Wey, C. C.

2000-11-01

171

Comparison Of Quantum Mechanical And Classical Trajectory Calculations Of Cross Sections For Ion-Atom Impact Ionization of Negative - And Positive -Ions For Heavy Ion Fusion Applications  

SciTech Connect

Stripping cross sections in nitrogen have been calculated using the classical trajectory approximation and the Born approximation of quantum mechanics for the outer shell electrons of 3.2GeV I{sup -} and Cs{sup +} ions. A large difference in cross section, up to a factor of six, calculated in quantum mechanics and classical mechanics, has been obtained. Because at such high velocities the Born approximation is well validated, the classical trajectory approach fails to correctly predict the stripping cross sections at high energies for electron orbitals with low ionization potential.

Igor D. Kaganovich; Edward A. Startsev; Ronald C. Davidson

2003-05-15

172

A Micro-Orifice Volatilization Impactor coupled to a Chemical Ionization Mass Spectrometer for the detection of organic acids in atmospheric aerosol particles  

NASA Astrophysics Data System (ADS)

Significant uncertainties related to sources and removal processes of particulate organic matter persist due, in part, to a poor understanding of the molecular-level composition. To address these issues, we are developing a novel technique that couples a micro-orifice volatilization impactor (MOVI) to a chemical ionization mass spectrometer (CIMS) for fast, in situ measurements of specific organic acids expected to be in atmospheric particles. The MOVI-CIMS process has three steps: 1) aerosol collection by inertial impaction, 2) volatilization and sample transfer, and 3) chemical ionization and detection using a quadrupole mass spectrometer. We present results from laboratory characterization of two MOVI designs, one operating at low pressure (60 Torr) and the other at near ambient pressure. The low-pressure impactor has a theoretical cut point of 40nm while the atmospheric pressure impactor (API) has a theoretical cut point of 280nm with a pressure drop of less than 5%. We compare the advantages and disadvantages of these two designs in terms of typical atmospheric particle size distributions. Experimental tests of their theoretical cut-points are used to assess the importance of jet-to- plate distance and particle bounce. In addition, we demonstrate the utility of the MOVI-CIMS technique by employing it in studies of heterogeneous oxidation of particle organics and of secondary organic aerosol formation from biogenic hydrocarbon oxidation. Based on typical signal-to-noise ratio, the MOVI-CIMS demonstrates a detection limit of ~50 ng for monocarboxylic acids when using the LPI version and the iodide ion as a chemical ionization reagent. Preliminary results suggest even lower detection limits are possible with other reagent ions.

Yatavelli, R. L.; Thornton, J. A.

2007-12-01

173

Application of gas chromatography-(triple quadrupole) mass spectrometry with atmospheric pressure chemical ionization for the determination of multiclass pesticides in fruits and vegetables.  

PubMed

A multi-residue method for the determination of 142 pesticide residues in fruits and vegetables has been developed using a new atmospheric pressure chemical ionization (APCI) source for coupling gas chromatography (GC) to tandem mass spectrometry (MS). Selected reaction monitoring (SRM) mode has been applied, acquiring three transitions for each compound. In contrast to the extensive fragmentation typically obtained in classical electron ionization (EI), the soft APCI ionization allowed the selection of highly abundant protonated molecules ([M+H](+)) as precursor ions for most compounds. This was favorable for both sensitivity and selectivity. Validation of the method was performed in which both quantitative and qualitative parameters were assessed using orange, tomato and carrot samples spiked at two levels, 0.01 and 0.1mg/kg. The QuEChERS method was used for sample preparation, followed by a 10-fold dilution of the final acetonitrile extract with a mixture of hexane and acetone. Recovery and precision were satisfactory in the three matrices, at both concentration levels. Very low limits of detection (down 0.01?g/kg for the most sensitive compounds) were achieved. Ion ratios were consistent and identification according to EU criteria was possible in 80% (0.01mg/kg) to 96% (0.1mg/kg) of the pesticide/matrix combinations. The method was applied to the analysis of various fruits and vegetables from the Mediterranean region of Spain. PMID:24070626

Cherta, Laura; Portolés, Tania; Beltran, Joaquim; Pitarch, Elena; Mol, Johannes G J; Hernández, Félix

2013-11-01

174

Detection of singly ionized state of two-electron tin centers with negative correlation energy in Pb{sub 1-x}Sn{sub x}S alloys  

SciTech Connect

The dependence of the concentration of the Sn{sup 3+} intermediate charge state of two-electron tin centers with negative correlation energy in PbS on the correlation energy is obtained according to the Gibbs distribution. It is shown that this tin state can be detected using Moessbauer spectroscopy for the {sup 119}Sn isotope at high temperatures.

Castro, R. A.; Nemov, S. A.; Seregin, P. P. [Herzen State Pedagogical University of Russia (Russian Federation)

2006-08-15

175

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.

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

2014-01-01

176

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

177

Interfacing microsampling droplets and mass spectrometry by paper spray ionization for online chemical monitoring of cell culture.  

PubMed

In this work, the establishment of a microdialysis-paper spray ionization-mass spectrometry (MS) system was described. A homemade microdialysis module was employed for sampling, and microdroplets were generated at the outlet of the capillary conducting the dialysate. Online MS analysis of each microdroplet was immediately accomplished, interfacing by paper spray ionization. Analytical performance of the method was investigated and improved through the introduction of thinner capillary tubes and the optimization of spray solvent and paper substrate. For microdroplets with concentrated salt at 50 nL, the limit of detection at 0.8 ppm (or 40 pg absolute) and a highest resolution at about 1.5 s were achieved. The integrated system was applied into the online monitoring of glucose concentration in cell culture mediums. A satisfactory linearity of the calibration curve between the relative MS intensity and the glucose concentration was observed. Furthermore, as a model, hormone regulation of the glucose concentration was investigated. This work demonstrated the potential application of the label-free, online "MS sensor" into studies on cellular metabolism. PMID:24949883

Liu, Wu; Wang, Niejun; Lin, Xuexia; Ma, Yuan; Lin, Jin-Ming

2014-07-15

178

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

179

Optimization of Routine Identification of Clinically Relevant Gram-Negative Bacteria by Use of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry and the Bruker Biotyper  

PubMed Central

Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) might complement and one day replace phenotypic identification of bacteria in the clinical microbiology laboratory, but there is no consensus standard regarding the requirements for its validation prior to clinical use in the United States. The objective of this study was to assess the preanalytical variables influencing Gram-negative identification by use of the Bruker Biotyper MALDI-TOF MS system, including density of organism spotting on a stainless steel target plate and the direct overlay of organisms with formic acid. A heavy smear with formic acid overlay was either superior or equivalent to alternative smear conditions. Microbiological preanalytical variables were also assayed, such as culture medium, growth temperature, and use of serial subculture. Postanalytical analysis included the application of modified species-level identification acceptance criteria. Biotyper identifications were compared with those using traditional phenotypic methods, and discrepancies were resolved with 16S rRNA gene sequencing. Compared to the recommended score cutoffs of the manufacturer, the application of optimized Biotyper score cutoffs for species-level identification increased the rate of identification by 6.75% for the enteric Gram-negative bacteria and 4.25% for the nonfermenting Gram-negative bacteria. Various incubation temperatures, growth medium types, and repeat subcultures did not result in misidentification. We conclude that the Bruker MALDI Biotyper is a robust system for the identification of Gram-negative organisms in the clinical laboratory and that meaningful performance improvements can be made by implementing simple pre- and postanalytical techniques. PMID:23426923

Ford, Bradley A.

2013-01-01

180

[Isolation and purification of solanesol from potato leaves by high-speed counter-current chromatography and identification by atmospheric pressure chemical ionization mass spectrometry].  

PubMed

Preparative high-speed counter-current chromatography (HSCCC) was used for the isolation and purification of solanesol from potato leaves. Experimental conditions of the extraction of solanesol from potato leaves have been optimized. An ultrafine extraction method was applied in this study. The efficiency using an ultrafine extraction was found to be improved in the investigation, the yields of solanesol by different extraction methods were 0.083% by ultrafine extraction and 0.050% by ultrasonic extraction. Using n-hexane-methanol (10:7, v/v) as the two-phase solvent system, preparative HSCCC was successfully performed with the yield of 5 mg solanesol at 98.7% of purity from 60 mg of crude extract in the one-step separation. The mobile phase was the lower phase and operated at a flow rate of 1.5 mL/min, while the apparatus rotated at 800 r/min. The solanesol was identified by the atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The ionization and cleavage mechanisms of solanesol in APCI-MS and APCI-MS/MS are discussed. PMID:17970112

Hu, Jiangyong; Liang, Yong; Xie, Ya; Huang, Zhaofeng; Zhong, Hanzuo

2007-07-01

181

Chemical vapor deposition of aminopropyl silanes in microfluidic channels for highly efficient microchip capillary electrophoresis-electrospray ionization-mass spectrometry.  

PubMed

We describe a chemical vapor deposition (CVD) method for the surface modification of glass microfluidic devices designed to perform electrophoretic separations of cationic species. The microfluidic channel surfaces were modified using aminopropyl silane reagents. Coating homogeneity was inferred by precise measurement of the separation efficiency and electroosmotic mobility for multiple microfluidic devices. Devices coated with (3-aminopropyl)di-isopropylethoxysilane (APDIPES) yielded near diffusion-limited separations and exhibited little change in electroosmotic mobility between pH 2.8 and pH 7.5. We further evaluated the temporal stability of both APDIPES and (3-aminopropyl)triethoxysilane (APTES) coatings when stored for a total of 1 week under vacuum at 4 °C or filled with pH 2.8 background electrolyte at room temperature. Measurements of electroosmotic flow (EOF) and separation efficiency during this time confirmed that both coatings were stable under both conditions. Microfluidic devices with a 23 cm long, serpentine electrophoretic separation channel and integrated nanoelectrospray ionization emitter were CVD coated with APDIPES and used for capillary electrophoresis (CE)-electrospray ionization (ESI)-mass spectrometry (MS) of peptides and proteins. Peptide separations were fast and highly efficient, yielding theoretical plate counts over 600,000 and a peak capacity of 64 in less than 90 s. Intact protein separations using these devices yielded Gaussian peak profiles with separation efficiencies between 100,000 and 400,000 theoretical plates. PMID:24655020

Batz, Nicholas G; Mellors, J Scott; Alarie, Jean Pierre; Ramsey, J Michael

2014-04-01

182

Unusual mechanism for H{sub 3}{sup +} formation from ethane as obtained by femtosecond laser pulse ionization and quantum chemical calculations  

SciTech Connect

The formation of H{sub 3}{sup +} from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H{sub 3}{sup +} formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H{sub 3}{sup +} ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H{sub 2} molecule attached to a C{sub 2}H{sub 4}{sup 2+} entity but IRC calculations show that it belongs to the reaction channel yielding C{sub 2}H{sub 3}{sup +}+ H{sub 3}{sup +}. Experimentally measured kinetic energies of the correlated H{sub 3}{sup +} and C{sub 2}H{sub 3}{sup +} ions confirm the reaction path suggested by theory.

Kraus, Peter M.; Schwarzer, Martin C.; Schirmel, Nora; Urbasch, Gunter; Frenking, Gernot; Weitzel, Karl-Michael [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35032 Marburg (Germany)

2011-03-21

183

High-throughput walkthrough detection portal for counter terrorism: detection of triacetone triperoxide (TATP) vapor by atmospheric-pressure chemical ionization ion trap mass spectrometry.  

PubMed

With the aim of improving security, a high-throughput portal system for detecting triacetone triperoxide (TATP) vapor emitted from passengers and luggage was developed. The portal system consists of a push-pull air sampler, an atmospheric-pressure chemical ionization (APCI) ion source, and an explosives detector based on mass spectrometry. To improve the sensitivity of the explosives detector, a novel linear ion trap mass spectrometer with wire electrodes (wire-LIT) is installed in the portal system. TATP signals were clearly obtained 2?s after the subject under detection passed through the portal system. Preliminary results on sensitivity and throughput show that the portal system is a useful tool for preventing the use of TATP-based improvised explosive devices by screening persons in places where many people are coming and going. PMID:21818804

Takada, Yasuaki; Nagano, Hisashi; Suzuki, Yasutaka; Sugiyama, Masuyuki; Nakajima, Eri; Hashimoto, Yuichiro; Sakairi, Minoru

2011-09-15

184

HPLC-PAD-atmospheric pressure chemical ionization-MS metabolite profiling of cytotoxic carotenoids from the echinoderm Marthasterias glacialis (spiny sea-star).  

PubMed

An HPLC-PAD-atmospheric pressure chemical ionization-MS metabolite profiling analysis was conducted on the marine echinoderm Marthasterias glacialis (spiny sea-star). Bio-guided purification of the methanolic extract led to the isolation of several carotenoids, namely zeaxanthin, astaxanthin and lutein. These compounds were characterized using both UV-Vis characteristics and MS spectra interpretation. No previous works addressed the MS analysis of carotenoids present in this organism. The purified carotenoid fraction displayed a strong cell proliferation inhibition against rat basophilic leukemia RBL-2H3 (IC(25)=268 microg/mL) cancer cell line. Against healthy V79 (rat lung fibroblasts (IC(25)=411 microg/mL)) cell line, however, toxicity was lower, as it is desired for anti-cancer molecules. This study suggests that M. glacialis may constitute a good source of bioactive compounds that can be used as lead compounds for the pharmaceutical industry. PMID:20574958

Ferreres, Federico; Pereira, David M; Gil-Izquierdo, Angel; Valentão, Patrícia; Botelho, João; Mouga, Teresa; Andrade, Paula B

2010-08-01

185

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

186

Negative atmospheric pressure chemical ionisation low-energy collision activation mass spectrometry for the characterisation of flavonoids in extracts of fresh herbs  

Microsoft Academic Search

The flavonoid composition of commonly eaten fresh herbs such as dill, oregano and parsley was analysed by combined LC, MS and low-energy collision induced dissociation (CID) MS–MS. Negative atmospheric pressure chemical ionisation (APCI) MS and MS–MS were used to provide molecular mass information and product-ion spectra of the glycosyl compounds. The most prominent fragment was found to arise from the

Ulla Justesen

2000-01-01

187

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

188

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

189

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

190

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

191

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

192

Kelvin spray ionization.  

PubMed

A novel self-powered dual spray ionization source has been developed for applications in mass spectrometry. This new source does not use any power supply and produces both positive and negative ions simultaneously. The idea behind this ionization source comes from the Kelvin water dropper. The source employs one or two syringes, two pneumatic sprays operated over a range of flow rates (0.15-15 ?L min(-1)) and gas pressures (0-150 psi), and two double layered metal screens for ion formation. A variable electrostatic potential from 0 to 4 kV can be produced depending on solvent and gas flow rates that allow gentle ionization of compounds. There are several parameters that affect the performance during ionization of molecules including the flow rate of solvent, gas pressure, solvent acidity, position of spray and metal screens with respect to each other and distance between metal screens and the counter electrode. This ionization method has been successfully applied to solutions of peptides, proteins and non-covalent complexes. In comparison with ESI, the charge number of the most populated state is lower than that from ESI. It indicates that this is a softer ionization technique and it produces more protein ions with folded structures. The unique features of Kelvin spray ionization (KeSI) are that the method is self-powered and ionization occurs at very low potentials by providing very low internal energy to the ions. This advantage can be used for the ionization of very fragile molecules and investigation of non-covalent interactions. PMID:24080942

Özdemir, Abdil; Lin, Jung-Lee; Gillig, Kent J; Chen, Chung-Hsuan

2013-11-21

193

Redox transformations in desorption electrospray ionization  

NASA Astrophysics Data System (ADS)

Redox changes occur in some circumstances when organic compounds are analyzed by desorption electrospray ionization mass spectrometry (DESI-MS). However, these processes are limited in scope and the data presented here suggest that there are only limited analogies between the redox behavior in DESI and the well-known solution-phase electrochemical processes in standard electrospray ionization (ESI). Positive and negative ion modes were both investigated and there is a striking asymmetry between the incidence of oxidation and of reduction. Although in negative ion mode DESI experiments, some aromatic compounds were ionized as odd-electron anion radicals, examples of full reduction were not found. By contrast, oxidation in the form of oxygen atom addition (or multiple oxygen atom additions) was observed for several different analytes. These oxidation reactions point to chemically rather than electrochemically controlled processes. Data is presented which suggests that oxidation is predominantly caused by reaction with discharge-created gas-phase radicals. The fact that common reducing agents and known antioxidants such as ascorbic acid are not modified, while a saturated organic acid like stearic acid is oxidized in DESI, indicates that the usual electrochemical redox reactions are not significant but that redox chemistry can be induced under special experimental conditions.

Benassi, Mario; Wu, Chunping; Nefliu, Marcela; Ifa, Demian R.; Volný, Michael; Cooks, R. Graham

2009-02-01

194

Negative necrotaxis.  

PubMed

We studied necrotaxis in several strains of protists and compared the reaction of living cells in the vicinity of cells killed by a ruby laser. Negative necrotaxis was observed for the unicellular green alga Euglena gracilis, whereas Chlamydomonas was shown to exhibit positive necrotaxis. The cellular colony Pandorina morum exhibited no reaction to the killing of nearby colonies. Both the colorless cryptomonad Chilomonas paramecium and the ciliate Tetrahymena pyriformis exhibited negative necrotaxis following the lysis of vitally stained specimens of their own species. They also exhibited negative necrotaxis following the lysis of Euglena cells. It was also demonstrated that the cellular content of Euglena cells lysed by heat or by a mechanical procedure acts as a repellent to intact Euglena cells. These results suggest that the negative necrotaxis provoked in Euglena by the laser irradiation is probably due to the chemotactic effect produced by the release of cell content in the extracellular medium. This cell content could, according to its chemical composition, act either as a repellent, an attractant, or be inactive. The sensitivity of cells (specific or nonspecific ion channels or chemoreceptors) are also of prime importance in the process. PMID:8400315

Ragot, R

1993-01-01

195

Remote sensing of chemical and physical processes in the atmosphere caused by the presence of radioactive ionization source  

NASA Astrophysics Data System (ADS)

During the years of the nuclear power industry, some large accidents occurred at the nuclear objects, and that caused enormous environmental contamination. The last accident at the Fucushima-1 power plant highlighted the need to review seriously the safety issues at the active power plants and to develop the new effective methods for remote detection and control over radioactive environmental contamination and over general geophysical situation in the areas. The main influence of the fission products on the environment is its ionisation, and therefore various detectable biological and physical processes that are caused by ions. Presence of an ionisation source within the area under study may cause significant changes of absolute humidity and, that is especially important, changes of the chemical potential of atmosphere vapours indicating presence of charged condensation centres. These effects may cause anomalies in the IR radiation emitted from the Earth surface and jumps in the chemical potentials of water vapours that may be observed by means of the satellite remote sensing by specialized equipment (works by Dimitar Ouzounov, Sergey Pulinets, e.a.). In the current study, the theoretical description is presented from positions of the molecular-kinetic condensation theory that shows significant changes of the absolute and relative humidity values in the near-earth air layer. The detailed calculations of the water vapours in atmosphere were carried out with use of detailed non-stationary kinetic model of moist atmosphere air. The processes of condensation and evaporation were effectively considered with use of reactions of neutral water molecules’ association under presence of a third particle, conversion of water molecules with an ion cluster to a more complicated cluster, and the relevant counter reactions’ splits of neutral and ion clusters.

Boyarchuk, Kirill; Tumanov, Mikhail; Karelin, Alexander

196

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

197

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

198

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. 14 figs.

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

1984-12-04

199

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

200

The role of physical and chemical properties of Pd nanostructured materials immobilized on inorganic carriers on ion formation in atmospheric pressure laser desorption/ionization mass spectrometry.  

PubMed

Fundamental parameters influencing the ion-producing efficiency of palladium nanostructures (nanoparticles [Pd-NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono-crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface-assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd-NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd-NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd-NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions. PMID:24913399

Silina, Yuliya E; Koch, Marcus; Volmer, Dietrich A

2014-06-01

201

Gas chromatography-atmospheric pressure chemical ionization-time of flight mass spectrometry for profiling of phenolic compounds in extra virgin olive oil.  

PubMed

A new analytical approach based on gas chromatography coupled to atmospheric pressure chemical ionization-time of flight mass spectrometry was evaluated for its applicability for the analysis of phenolic compounds from extra-virgin olive oil. Both chromatographic and MS parameters were optimized in order to improve the sensitivity and to maximize the number of phenolic compounds detected. We performed a complete analytical validation of the method with respect to its linearity, sensitivity, precision, accuracy and possible matrix effects. The LODs ranged from 0.13 to 1.05ppm for the different tested compounds depending on their properties. The RSDs for repeatability test did not exceed 6.07% and the accuracy ranged from 95.4% to 101.5%. To demonstrate the feasibility of our method for analysis of real samples, we analyzed the extracts of three different commercial extra-virgin olive oils. We have identified unequivocally a number of phenolic compounds and obtained quantitative information for 21 of them. In general, our results show that GC-APCI-TOF MS is a flexible platform which can be considered as an interesting tool for screening, structural assignment and quantitative determination of phenolic compounds from virgin olive oil. PMID:21241992

García-Villalba, Rocío; Pacchiarotta, Tiziana; Carrasco-Pancorbo, Alegría; Segura-Carretero, Antonio; Fernández-Gutiérrez, Alberto; Deelder, André M; Mayboroda, Oleg A

2011-02-18

202

Liquid chromatography/atmospheric pressure chemical ionization ion trap mass spectrometry of bilobalide in plasma and brain of rats after oral administration of its phospholipidic complex.  

PubMed

Standardized extracts of Ginkgo biloba L. leaves are widely used in clinical practice for the symptomatic treatment of mild to moderate dementia syndromes, cerebral insufficiency and for the enhancement of cognitive function. The main active components present in G. biloba extracts are flavonol-glycosides and terpene-lactones. In recent investigations, the sesquiterpene trilactone bilobalide has been described to exert an interesting neuroprotective effect when administered systemically to experimental animals. Oral administration of terpene-lactones either as standardized extracts or purified products is characterized by a low bioavailability. While preparing phospholipidic complex of G. biloba extracts or bilobalide, plasma levels of terpenes and sesquiterpene increase. In the present study, phospholipidic complex of bilobalide (IDN 5604) has been administered orally to rats and bilobalide levels have been determined in plasma and brain by means of a validated method based on liquid chromatography coupled to atmospheric pressure chemical ionization ion trap mass spectrometry (LC/APCI-ITMS). Due to its sensitivity (about 3pmol/ml) and specificity, LC/APCI-ITMS method proved to be a very powerful tool for pharmacokinetic studies of Ginkgo terpene-lactones. The results of the present study clearly confirm the improvement of oral bioavailability of bilobalide administered as phospholipidic complex and, for the first time, demonstrate the detection of significative amounts of bilobalide in brain. This last finding agrees with the neuroprotective activity observed for bilobalide. PMID:19473802

Rossi, Rossana; Basilico, Fabrizio; Rossoni, Giuseppe; Riva, Antonella; Morazzoni, Paolo; Mauri, Pier Luigi

2009-09-01

203

The determination of cyclophosphamide and its metabolites in blood plasma as stable trifluoroacetyl derivatives by electron capture chemical ionization gas chromatography/mass spectrometry.  

PubMed

A method is described for the determination of the antitumour drug cyclophosphamide and six stable metabolites in plasma of cancer patients, namely dechloroethyl-cyclophosphamide, 4-keto-cyclophosphamide, carboxy-phosphamide, alcophosphamide, nor-nitrogen mustard and the N-chloroethyl-1,3-oxazolidine-2-one, as methyl and/or trifluoroacetyl derivatives by single ion monitoring gas chromatography/mass spectrometry, mostly in the electron capture chemical ionization mode. The isolation of most metabolites was performed by solid-phase C-18 extraction in weakly acidic medium. The phosphoramide mustard isolated under these conditions decomposes readily to the nor-nitrogen mustard during derivatization. The original nor-nitrogen mustard and the chloroethyl-1,3-oxazolidine-2-one were isolated by liquid extraction with ethyl acetate in alkaline medium. Recoveries of 75-99% were measured using spiked blank plasma samples. Quantitation of metabolites in patient plasma samples was performed using two sets of calibration curves for the concentration ranges of 1-100 ng and 0.1-10 micrograms of metabolite per millilitre of original plasma. PMID:8148406

Momerency, G; Van Cauwenberghe, K; Slee, P H; Van Oosterom, A T; De Bruijn, E A

1994-03-01

204

Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection.  

PubMed

In this paper the application of on-line HPLC-UV-APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of beta-carotene is reported. All HPLC separations were carried out under RP conditions on self-synthesized polymeric C30 phases. The analysis of a carotenoid mixture containing astaxanthin, canthaxanthin, zeaxanthin, echinenone and beta-carotene by HPLC-APCI-MS was achieved by scanning the mass range from m/z 200 to 700. For the characterization of a sample containing cis/trans isomers of beta-carotene as well as their oxidation products, a photodiode-array UV-visible absorbance detector was used in addition between the column and the mass spectrometer for structural elucidation of the geometrical isomers. The detection limit for beta-carotene in positive-ion APCI-MS was determined to be 1 pmol. In addition, an extract of non-polar substances in vegetable juice has been analyzed by HPLC-APCI-MS. The included carotenoids could be identified by their masses and their retention times. PMID:10497926

Lacker, T; Strohschein, S; Albert, K

1999-08-27

205

Trace analysis of selected hormones and sterols in river sediments by liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

In this paper, development and optimization of new LC-MS method for determination of twenty selected hormones, human/animal and plant sterols in river sediments were described. Sediment samples were prepared using ultrasonic extraction and clean up with silica gel/anhydrous sodium sulphate cartridge. Extracts were analyzed by liquid chromatography-linear ion trap-tandem mass spectrometry, with atmospheric pressure chemical ionization. The optimized extraction parameters were extraction solvent (methanol), weight of the sediment (2g) and time of ultrasonic extraction (3× 10min). Successful chromatographic separation of hormones (estriol and estrone, 17?- and 17?-estradiol) and four human/animal sterols (epicoprostanol, coprostanol, ?-cholestanol and ?-cholestanol) that have identical fragmentation reactions was achieved. The developed and optimized method provided high recoveries (73-118%), low limits of detection (0.8-18ngg(-1)) and quantification (2.5-60ngg(-1)) with the RSDs generally lower than 20%. Applicability of the developed method was confirmed by analysis of six river sediment samples. A widespread occurrence of human/animal and plant sterols was found. The only detected hormone was mestranol in just one sediment sample. PMID:25182857

Mati?, Ivana; Gruji?, Svetlana; Jaukovi?, Zorica; Lauševi?, Mila

2014-10-17

206

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

NASA Astrophysics Data System (ADS)

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 flight by adding HNO3 from a calibrated HNO3 permeation source into the sample air flow, and instrument background is measured by displacing ambient air from the sampling inlet with a flow of dry nitrogen in the sampling inlet. Instrument temperatures, pressures, and gas flows are controlled in flight to maintain a constant detection sensitivity in a changing ambient operating environment. The initial performance of this new instrument is evaluated using HNO3 and ozone data obtained between 6 and 19 km during the 1999 NASA Atmospheric Chemistry of Combustion Emissions Near the Tropopause mission. The data reveal a sensitivity of 0.73 Hz/pptv, a detection limit of 30 pptv for 10 s integration times, and a fast time response (<1 s). Further reductions in the background HNO3 signal will improve performance.

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

2000-10-01

207

GC/MS-positive ion chemical ionization and MS/MS study of volatile benzene compounds in five different woods used in barrel making.  

PubMed

Extracts from acacia, chestnut, cherry, mulberry, and oak wood, used in making barrels for aging wine and spirits were studied by GC/MS positive ion chemical ionization (PICI). Wood chips were extracted by a 50% water/ethanol solution and a tartrate buffer pH 3.2-12% ethanol (model wine) solution. The principal compounds identified in extracts were guaiacol-containing aldehydes and alcohols, such as benzaldehyde and derivatives, vanillin and syringaldehyde, cinnamaldehyde and coniferaldehyde, eugenol and methoxyeugenol, guaiacol and methoxyguaiacol derivatives. PICI using methane as reagent gas produced a high yield of the protonated molecular ion of volatile phenols, compound identification was confirmed by collision-induced-dissociation (CID) experiments on [M + H](+) species. MS/MS fragmentation patterns were studied with standard compounds: guaiacol-containing molecules were characterized by neutral methyl and methanol losses, benzaldehyde derivatives by CO loss. Acacia wood extracts contained significant syringaldehyde and anisaldehyde, but no eugenol and methoxyeugenol. Significant syringaldehyde, eugenol and methoxyeugenol, and high vanillin were found in chestnut and oak wood extracts; low presence of volatile benzene compounds was found in mulberry wood extracts. Cherry wood extracts were characterized by the presence of several benzaldehyde derivatives and high trimethoxyphenol. PMID:17370248

Flamini, Riccardo; Dalla Vedova, Antonio; Cancian, Davide; Panighel, Annarita; De Rosso, Mirko

2007-05-01

208

Screening of pesticides and polycyclic aromatic hydrocarbons in feeds and fish tissues by gas chromatography coupled to high-resolution mass spectrometry using atmospheric pressure chemical ionization.  

PubMed

This paper reports a wide-scope screening for detection and identification of pesticides and polycyclic aromatic hydrocarbons (PAHs) in feeds and fish tissues. QuEChERS sample treatment was applied, using freezing as an additional cleanup. Analysis was carried out by gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI) QTOF MS). The qualitative validation was performed for over 133 representative pesticides and 24 PAHs at 0.01 and 0.05 mg/kg. Subsequent application of the screening method to aquaculture samples made it possible to detect several compounds from the target list, such as chlorpyrifos-methyl, pirimiphos-methyl, and ethoxyquin, among others. Light PAHs (?4 rings) were found in both animal and vegetable samples. The reliable identification of the compounds was supported by accurate mass measurements and the presence of at least two representative m/z ions in the spectrum together with the retention time of the peak, in agreement with the reference standard. Additionally, the search was widened to include other pesticides for which standards were not available, thanks to the expected presence of the protonated molecule and/or molecular ion in the APCI spectra. This could allow the detection and tentative identification of other pesticides different from those included in the validated target list. PMID:24559176

Nácher-Mestre, Jaime; Serrano, Roque; Portolés, Tania; Berntssen, Marc H G; Pérez-Sánchez, Jaume; Hernández, Félix

2014-03-12

209

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

210

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

211

Studies of the role of metastables and doubly ionized species in the chemical and thermal structure of the Venusian and Martian ionospheres  

NASA Technical Reports Server (NTRS)

Models of the upper atmospheres of Mars and Venus were constructed using Viking and Pioneer Venus data. The neutral densities, with the exception of NO, N(4S), N(2D) and N(2P) were taken from the measured values, along with the neutral, ion, and electron temperatures. Using solar fluxes and relevant cross sections, the production rates of ions and neutral fragments by photo and electron impact processes were computed. These production rates were combined with chemical production rates and loss along with one dimensional transport eddy diffusion, molecular and ambi polar diffusion, and thermal diffusion, to determine the densities of ions and odd nitrogen species. Preliminary calculations show that the chemistry of metastables and doubly ionized species is important in the ionospheres of Mars and Venus. Production of N(+) in metastable reactions is particularly important, and it explains the discrepancy between the measurements of earlier models. Production of CO(+) is also affected. Reactions of O(++) and O(+)(2D) with N2 have important consequences for the escape rate of atomic nitrogen from the Martian atmosphere.

Fox, J. L.

1981-01-01

212

Characterization of gamma-irradiated polyethylene terephthalate by liquid-chromatography mass-spectrometry (LC MS) with atmospheric-pressure chemical ionization (APCI)  

NASA Astrophysics Data System (ADS)

Low-molecular-weight (low-MW) constituents of polyethylene terephthalate (PET), irradiated with 60Co gamma rays at 25 and 50 kGy, were analyzed by HPLC-MS with atmospheric-pressure chemical ionization (APCI). Consistent with earlier results, the concentrations of the major compounds that are present in the non-irradiated PET do not change perceptibly. However, we find a small but significant increase in terephthalic acid ethylester, from less than 1 mg/kg in the non-irradiated control to ca. 2 mg/kg after 50 kGy, which has not been described before. The finding is important because it gives an impression of the sensitivity of the analytical method. Additionally, it shows that even very radiation-resistant polymers can form measurable amounts of low-MW radiolysis products. The potential and limitations of LC-MS for the analysis of radiolysis products and unidentified migrants are briefly discussed in the context of the question: How can we validate our analytical methods for unknown analytes?

Buchalla, Rainer; Begley, Timothy H.

2006-01-01

213

Part-per-trillion level determination of antifouling pesticides and their byproducts in seawater samples by off-line solid-phase extraction followed by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

A new method for the simultaneous determination of antifouling pesticides and some of their byproducts such as dichlofluanid, diuron and its byproducts [demethyldiuron and 1-(3,4-dichlorophenyl)urea], (2-thiocyanomethylthio)ben: zothiazole, chlorothalonil, Sea-nine 211, Irgarol 1051 and one of its byproducts (2-methylthio-4-tert.-butylamino-s-triazine) in seawater was developed. The extraction of these compounds from the filtered seawater samples was performed off-line with different solid-phase extraction sorbents using (I) a 500 mg graphitized carbon black cartridge (ENVI-Carb) and (II) 200 mg polymeric cartridges (LiChrolut EN and Isolute ENV+) and passing 500 ml of the sample through these cartridges. The detection was carried out by reversed-phase high-performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry both in the negative and positive ion modes. The recovery ranged from 76 to 96% for the whole antifouling group with the ENVI-Carb cartridges and the detection limit was at the part-per-trillion level except for TCMTB. The method utilizing the polymeric cartridge proved to be very useful, time saving and with good recoveries when only Irgarol and its byproduct, Sea-nine 211 and diuron and its byproducts, have to be analyzed. The different cartridges were applied to the analysis of these pesticides in different marinas of the Catalan coast; diuron, dichlofluanid, Sea-nine 211, Irgarol as well as demethyldiuron and the Irgarol byproduct being the must ubiquitous pollutants. Maximum concentration levels were 2-3.5 microg/l of diuron and Sea-nine 211, respectively. PMID:10870693

Martínez, K; Ferrer, I; Barceló, D

2000-05-19

214

Determination of trace levels of pyrethroid metabolites in human urine by capillary gas chromatography-high resolution mass spectrometry with negative chemical ionization  

Microsoft Academic Search

Summary  Applications of high-resolution gas chromatography and high-resolution mass spectrometry (GC-MS) for identification and quantitation\\u000a of trace amounts of pyrethroid metabolites in human urine samples are demonstrated. The method covers the pyrethroid metabolitescis- andtrans-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane carboxylic acid (cis- andtrans-DCCA),cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis-DBCA), 4-fluoro-3-phenoxybenzoic acid (FPBA), and 3-phenoxybenzoic acid (3-PBA). After acid-induced hydrolysis of urine samples\\u000a and exhaustive solvent extraction, a carbodiimide-coupled esterification

G. Leng; K.-H. Kühn; A. Leng; W. Gries; J. Lewalter; H. Idel

1997-01-01

215

Heat Stress Evaluation of Two-layer Chemical Demilitarization Ensembles with a Full Face Negative Pressure Respirator.  

PubMed

The purpose of this study was to examine the heat stress effects of three protective clothing ensembles: (1) protective apron over cloth coveralls including full face negative pressure respirator (APRON); (2) the apron over cloth coveralls with respirator plus protective pants (APRON+PANTS); and (3) protective coveralls over cloth coveralls with respirator (PROTECTIVE COVERALLS). In addition, there was a no-respirator ensemble (PROTECTIVE COVERALLS-noR), and WORK CLOTHES as a reference ensemble. Four acclimatized male participants completed a full set of five trials, and two of the participants repeated the full set. The progressive heat stress protocol was used to find the critical WBGT (WBGTcrit) and apparent total evaporative resistance (Re,T,a) at the upper limit of thermal equilibrium. The results (WBGTcrit [°C-WBGT] and Re,T,a [kPa?m(2) W(-1)]) were WORK CLOTHES (35.5, 0.0115), APRON (31.6, 0.0179), APRON+PANTS (27.7, 0.0244), PROTECTIVE COVERALLS (25.9, 0.0290), and PROTECTIVE COVERALLS-noR (26.2, 0.0296). There were significant differences among the ensembles. Supporting previous studies, there was little evidence to suggest that the respirator contributed to heat stress. PMID:24705801

Fletcher, Oclla Michele; Guerrina, Ryan; Ashley, Candi D; Bernard, Thomas E

2014-09-11

216

Heat Stress Evaluation of Two-layer Chemical Demilitarization Ensembles with a Full Face Negative Pressure Respirator  

PubMed Central

The purpose of this study was to examine the heat stress effects of three protective clothing ensembles: (1) protective apron over cloth coveralls including full face negative pressure respirator (APRON); (2) the apron over cloth coveralls with respirator plus protective pants (APRON+PANTS); and (3) protective coveralls over cloth coveralls with respirator (PROTECTIVE COVERALLS). In addition, there was a no-respirator ensemble (PROTECTIVE COVERALLS-noR), and WORK CLOTHES as a reference ensemble. Four acclimatized male participants completed a full set of five trials, and two of the participants repeated the full set. The progressive heat stress protocol was used to find the critical WBGT (WBGTcrit) and apparent total evaporative resistance (Re,T,a) at the upper limit of thermal equilibrium. The results (WBGTcrit [°C-WBGT] and Re,T,a [kPa?m2 W?1]) were WORK CLOTHES (35.5, 0.0115), APRON (31.6, 0.0179), APRON+PANTS (27.7, 0.0244), PROTECTIVE COVERALLS (25.9, 0.0290), and PROTECTIVE COVERALLS-noR (26.2, 0.0296). There were significant differences among the ensembles. Supporting previous studies, there was little evidence to suggest that the respirator contributed to heat stress. PMID:24705801

FLETCHER, Oclla Michele; GUERRINA, Ryan; ASHLEY, Candi D.; BERNARD, Thomas E.

2014-01-01

217

Evaluation of the Bruker Biotyper and Vitek MS Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry Systems for Identification of Nonfermenting Gram-Negative Bacilli Isolated from Cultures from Cystic Fibrosis Patients  

PubMed Central

The Bruker Biotyper and Vitek MS matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (MS) instruments were evaluated for the identification of nonfermenting Gram-negative bacilli (NFGNB) by a blinded comparison to conventional biochemical or molecular methods. Two hundred NFGNB that were recovered from cultures from cystic fibrosis patients in the University of Iowa Health Care (UIHC) Microbiology Laboratory between 1 January 2006 and 31 October 2010 were sent to Mayo Clinic for analysis with the Bruker Biotyper (software version 3.0) and to bioMérieux for testing with Vitek MS (SARAMIS database version 3.62). If two attempts at direct colony testing failed to provide an acceptable MALDI-TOF identification, an extraction procedure was performed. The MS identifications from both of these systems were provided to UIHC for comparison to the biochemical or molecular identification that had been reported in the patient record. Isolates with discordant results were analyzed by 16S rRNA gene sequencing at UIHC. After discrepancy testing, the Bruker Biotyper result agreed with the biochemical or molecular method, with 72.5% of isolates to the species level, 5.5% to the complex level, and 19% to the genus level (3% not identified). The level of agreement for Vitek MS was 80% species, 3.5% complex, 6% genus, and 3.5% family (7% not identified). Both MS systems provided rapid (?3 min per isolate) and reliable identifications. The agreement of combined species/complex/genus-level identification with the reference method was higher for the Bruker Biotyper (97% versus 89.5%, P = 0.004) but required an extraction step more often. Species-level agreement with the reference method was similar for both MS systems (72.5% and 80%, P = 0.099). PMID:22495566

Marko, Daniel C.; Saffert, Ryan T.; Cunningham, Scott A.; Hyman, Jay; Walsh, John; Arbefeville, Sophie; Howard, Wanita; Pruessner, Jon; Safwat, Nedal; Cockerill, Franklin R.; Bossler, Aaron D.; Patel, Robin

2012-01-01

218

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

219

Chemical applications of topology and group theory. 29. Low density polymeric carbon allotropes based on negative curvature structures  

SciTech Connect

The construction of graphite and fullerene structures from networks of trigonal sp{sup 2} carbon atoms of zero and positive curvature can be extended to a fourth form of carbon, provisionally called schwarzites, consisting of networks of trigonal sp{sup 2} carbon atoms decorating infinite periodic minimal surfaces (IPMS`s) of negative curvature and topological genus 3 such as the so-called D and P surfaces. The carbon networks of the simplest schwarzite structures contain only six- and seven-membered rings. The stable structures of both fullerenes and schwarzites contain enough six-membered rings so that no two five-membered rings in the fullerene structures or no two seven-membered rings in the schwarzite structures share edges leading to unstable pentalene and heptalene units, respectively. The smallest unit cell of a viable schwarzite structure of this type contains 168 carbon atoms and is constructed by applying a leapfrog transformation to a genus 3 figure containing 24 heptagons and 56 vertices. Although this C{sub 168} schwarzite unit cell has local O{sub h} point group symmetry based on the cubic lattice of the D or P surface, its larger permutational symmetry group is the PSL(2,7) group of order 168 analogous to the icosahedral pure rotation group, I, of order 60 of the C{sub 60} fullerene considered as the isomorphous PSL(2,5) group. The porosity of the IPMS`s on which the schwarzite structures are based leads to predictions of unusually low density for this type of carbon allotrope. 38 refs., 11 figs., 5 tabs.

King, R.B. [Uinv. of Georgia, Athens, GA (United States)] [Uinv. of Georgia, Athens, GA (United States)

1996-09-12

220

Ionizing radiation  

NASA Technical Reports Server (NTRS)

The penetrating ionizing space radiations are found to be extremely diverse in the energy range of both their particulate and their electromagnetic components. Radiation terms and measures and ionizing radiation classes and sources are presented. Whole body radiation effects are examined, including radiation intensity and rate effectiveness factors. Radiation effects on specific body systems, such as blood, skin, visual, and reproductive systems are also discussed.

Warren, S.; Grahn, D.

1973-01-01

221

Enantioselective determination of cetirizine in human plasma by normal-phase liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

A highly sensitive and enantioselective method has been developed and validated for the determination of levocetirizine [(R)-cetirizine] in human plasma by normal-phase liquid chromatography coupled to tandem mass spectrometry with an atmospheric pressure chemical ionization (APCI) interface in the positive ion mode. Enantioselective separation was achieved on a CHIRALPAK AD-H column using an isocratic mobile phase consisting of a mixture of n-hexane, ethyl alcohol, diethylamine, and acetic acid (60:40:0.1:0.1, v/v/v/v). Levocetirizine-D(8) was used as an internal standard (IS). Levocetirizine and the IS were detected by multiple-reaction monitoring (MRM). Mass transitions of analyte and IS were m/z 389.2?201.1 and 397.2?201.1, respectively. Under optimized analytical conditions, a baseline separation of two enantiomers and IS was obtained in less than 11 min. Samples were prepared by a simple two-step extraction by protein precipitation using acetonitrile followed by liquid-liquid extraction with a n-hexane-dichloromethane mixture (50:50, v/v). The standard curve for levocetirizine was linear (r(2)>0.995) in the concentration range 0.5-300 ng/mL. Recovery was between 97.0 and 102.2% at low, medium, and high concentration. The limit of quantification (LOQ) was 0.5 ng/mL. Other method validation parameters, such as precision, accuracy, and stability, were very satisfactory. Finally, the proposed method was successfully applied to the study of enantioselective oral pharmacokinetics of levocetirizine in healthy Korean volunteers. PMID:21081290

Kang, Seung Woo; Jang, Hae Jong; Moore, Victor S; Park, Ji-Young; Kim, Kyoung-Ah; Youm, Jeong-Rok; Han, Sang Beom

2010-12-15

222

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

223

Determination and differentiation of triacylglycerol molecular species in Antarctic and non-Antarctic yeasts by atmospheric pressure-chemical ionization-mass spectrometry.  

PubMed

Yeast, particularly Saccharomyces cerevisiae, has long served as a model eukaryotic system for studies on the regulation of lipid metabolism. We developed a high performance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry method for the detailed analysis of triacylglycerols (TAGs) in 14 species of yeast consisting of seven Antarctic yeasts (grown at 15°C and 5°C) and seven non-Antarctic yeasts (grown at 25°C and 15°C), the latter including 3 strains of S. cerevisiae. Analysis of TAG molecular species established that the sn-2 position was invariably occupied by an unsaturated fatty acyl moiety. In S. cerevisiae the preference was for oleic acid 18:1>palmitoleic acid 16:1, in Candida albicans, Cryptococcus humicolus and Rhodotorula mucilaginosa 18:1>linoleic acid 18:2 and in Zygosaccharomyces rouxii 18:2>18:1. In the Antarctic yeasts (Cryptococcus watticus, Cryptococcus victoriae, Cryptococcus nyarrowii, Leucosporidium antarcticum, Leucosporidium fellii, Candida psychrophila and Rhodotorula mucilaginosa) the general pattern was for the sn-2 position to be occupied by 18:1, 18:2 or linolenic acid 18:3. A trend towards synthesis of increased unsaturated fatty acid in TAGs was observed as the growth temperature was lowered. The application of principal component analysis demonstrated that the yeasts were differentiated into three distinct groups. One group consisted of the three S. cerevisiae strains, a second the other four non-Antarctic yeasts and the third the seven Antarctic yeasts. The data for the Antarctic yeasts, to the best of our knowledge, have not been previously reported. PMID:23831436

Bhuiyan, Mohammad; Tucker, David; Watson, Kenneth

2013-09-01

224

Development and Comparison of Three Liquid Chromatography-Atmospheric Pressure Chemical Ionization/Mass Spectrometry Methods for Determining Vitamin D Metabolites in Human Serum  

PubMed Central

Liquid chromatographic methods with atmospheric pressure chemical ionization mass spectrometry were developed for the determination of the vitamin D metabolites 25-hydroxyvitamin D2 (25(OH)D2), 25-hydroxyvitamin D3 (25(OH)D3), and 3-epi-25-hydroxyvitamin-D3 (3-epi-25(OH)D3) in the four Levels of SRM 972, Vitamin D in Human Serum. One method utilized a C18 column, which separates 25(OH)D2 and 25(OH)D3, and one method utilized a CN column that also resolves the diastereomers 25(OH)D3 and 3-epi-25(OH)D3. Both methods utilized stable isotope labeled internal standards for quantitation of 25(OH)D2 and 25(OH)D3. These methods were subsequently used to evaluate SRM 909c Human Serum, and 25(OH)D3 was the only vitamin D metabolite detected in this material. However, SRM 909c samples contained matrix peaks that interfered with the determination of the [2H6]-25(OH)D3 peak area. The chromatographic conditions for the C18 column were modified to remove this interference, but conditions that separated the matrix peaks from [2H6]-25(OH)D3 on the CN column could not be identified. The alternate internal standard [2H3]-25(OH)D3 did not suffer from matrix interferences and was used for quantitation of 25(OH)D3 in SRM 909c. During the evaluation of SRM 909c samples, a third method was developed using a pentafluorophenylpropyl column that also separates the diastereomers 25(OH)D3 and 3-epi-25(OH)D3. The 25(OH)D3 was measured in SRM 909c using all three methods, and the results were compared. PMID:22533908

Bedner, Mary; Phinney, Karen W.

2012-01-01

225

Qualitative and quantitative analysis on chemical constituents from Curculigo orchioides using ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

A rapid ultra-high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-Q-TOF/MS) method was developed for qualitative and quantitative determination of constituents in the rhizome of Curculigo orchioides. Qualitative analysis was performed on a Waters ACQUITY UHPLC @ HSS T3 column (1.8?m 100×2.1mm) using gradient elution with mobile phase of 0.1% formic acid and acetonitrile. Quantitative analysis was performed on an Agilent ZORBAX Eclipse plus C18 column (1.7?m 100×2.1mm) using gradient elution with mobile phase of 0.1% acetic acid and acetonitrile for at least 20min. Quadrupole TOF/MS in either full scan mode or extracted ion mode was used for qualitative and quantitative analysis of the constituents. According to the mass spectrometric fragmentation mechanism and UHPLC-ESI-Q-TOF-MS data, chemical structures of 45 constituents in the rhizome of Curculigo orchioides, including 19 phenols and phenolic glycosides, 16 lignans and lignan glycosides, 8 triterpenoid saponins, one flavone and one sesquiterpene, were identified tentatively on-line without the time-consuming process of isolation. In addition, 8 phenolic glycosides including 5-hydroxymethylfurfural (HMF), 2-hydroxy-5-(2-hydroxyethyl) phenyl-?-d-glucopyranoside (HPG), anacardoside (ACD), orcinol glucoside (OGD), orcinol-1-O-?-d-apiofuranosyl-(1?6)-?-d-glucopyranoside (OAG), 2,6-dimethoxybenzoic acid (DBA), curculigoside (CUR) and curculigine A (CCL) were quantitated in 11 collected samples and 10 commercial samples from different providers. The results show that UHPLC-ESI-Q-TOF-MS is a viable method for analysis and quality evaluation of the constituents from the rhizome of Curculigo orchioides. PMID:25305598

He, Yongjing; Dong, Xin; Jia, Xiaoxuan; Li, Mei; Yuan, Tingting; Xu, Hongtao; Qin, Luping; Han, Ting; Zhang, Qiaoyan

2015-01-01

226

Aqueous-phase photooxidation of levoglucosan - a mechanistic study using aerosol time-of-flight chemical ionization mass spectrometry (Aerosol ToF-CIMS)  

NASA Astrophysics Data System (ADS)

Levoglucosan (LG) is a widely employed tracer for biomass burning (BB). Recent studies have shown that LG can react rapidly with hydroxyl (OH) radicals in the aqueous phase despite many mass balance receptor models assuming it to be inert during atmospheric transport. In the current study, aqueous-phase photooxidation of LG by OH radicals was performed in the laboratory. The reaction kinetics and products were monitored by aerosol time-of-flight chemical ionization mass spectrometry (Aerosol ToF-CIMS). Approximately 50 reaction products were detected by the Aerosol ToF-CIMS during the photooxidation experiments, representing one of the most detailed product studies yet performed. By following the evolution of mass defects of product peaks, unique trends of adding oxygen (+O) and removing hydrogen (-2H) were observed among the products detected, providing useful information for determining potential reaction mechanisms and sequences. Additionally, bond-scission reactions take place, leading to reaction intermediates with lower carbon numbers. We introduce a data analysis framework where the average oxidation state (OSc) is plotted against a novel molecular property: double-bond-equivalence-to-carbon ratio (DBE/#C). The trajectory of LG photooxidation on this plot suggests formation of polycarbonyl intermediates and their subsequent conversion to carboxylic acids as a general reaction trend. We also determined the rate constant of LG with OH radicals at room temperature to be 1.08 ± 0.16 × 109 M-1 s-1. By coupling an aerosol mass spectrometer (AMS) to the system, we observed a rapid decay of the mass fraction of organic signals at mass-to-charge ratio 60 (f60), corresponding closely to the LG decay monitored by the Aerosol ToF-CIMS. The trajectory of LG photooxidation on a f44-f60 correlation plot matched closely to literature field measurement data. This implies that aqueous-phase photooxidation might be partially contributing to aging of BB particles in the ambient atmosphere.

Zhao, R.; Mungall, E. L.; Lee, A. K. Y.; Aljawhary, D.; Abbatt, J. P. D.

2014-09-01

227

Determination and confirmation of malachite green and leucomalachite green residues in salmon using liquid chromatography/mass spectrometry with no-discharge atmospheric pressure chemical ionization.  

PubMed

A liquid chromatography/mass spectrometry (LC/MS) method was developed to quantitate and confirm residues of leucomalachite green (LMG) in salmon tissue after their conversion to chromic malachite green (MG) in the extraction process. The method uses no-discharge atmospheric pressure chemical ionization (APCI) in conjunction with an ion-trap instrument to generate product-ion spectra. In the sample preparation procedure, salmon tissue is extracted with acetonitrile/buffer, the LMG residue is partitioned into methylene chloride, the LMG is converted to MG using an organic oxidizing agent, and the MG is isolated on alumina/propylsulfonic acid solid-phase extraction cartridges. The method was validated by fortifying salmon with different levels of LMG, and then detecting the residue as MG The LC/MS conditions, including a comparison of electrospray and no-discharge APCI, were evaluated and optimized. MG was not confirmed in any of the control tissue extracts, and all fortified samples analyzed during validation met the confirmation criteria as described. In addition to providing confirmatory data, this method can provide an alternative method for quantitation of MG in salmon. The recoveries of LMG measured as MG by this LC/MS method, at fortification levels of 1-10 ng/g were very high (86-109%), with low relative standard deviation(RSD) values (6.4-13%). The results agreed very closely with those obtained for the same extracts using an LCNIS procedure, indicating that matrix suppression was not an issue. The presence of LMG in salmon tissue samples fortified at 0.25 ng/g was confirmed by this method, with an average recovery of 70.1% and an RSD of 12.0%. Sample extracts from fish exposed to MG were also analyzed. PMID:16385980

Turnipseed, Sherri B; Andersen, Wendy C; Roybal, José E

2005-01-01

228

Alfvén ionization in exoplanetary atmospheres  

NASA Astrophysics Data System (ADS)

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest such objects harbour an atmospheric, localized plasma. For lowmass objects, the degree of thermal ionization is insufficient to qualify the ionized gas as a plasma, posing the question: what ionization processes can efficiently produce the required plasma? We propose Alfvén ionization as a simple mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficiently large degrees of ionization (? 10^-7) that they constitute plasmas. We outline the criteria required for Alfvén ionization to occur and justify it's applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs and M-dwarfs for 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 ranging from 10^-6-1 can be obtained. 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 as a consequence of the Penning Effect. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models.

Stark, C. R.; Helling, Ch.; Diver, D. A.; Rimmer, P. B.

2013-09-01

229

Shock tube study of ionization rates of NaCl-contaminated argon  

NASA Technical Reports Server (NTRS)

Electron density, electron temperature, and concentration of excited sodium atoms are measured in the weakly ionized regime behind a shock wave in impure argon in a shock tube using microwave techniques and spectrally resolved radiometry. Evidence is presented to show that an apparent increase in the rate of ionization is due to electron detachment of negative chlorine ions produced from sodium chloride vapor contained as an impurity. To be consistent with this chemical model, rate coefficients are found in the temperature range between 5500 and 8600 K for the dissociation of NaCl into an ion pair, dissociation of NaCl into a neutral pair, and electron detachment of a negative chlorine ion. Electron temperature is lower than heavy-particle temperature by roughly 1000 K. The electron-argon impact-ionization rate coefficient is a weak function of electron temperature in contradiction to expectation.

Schneider, K.-P.; Park, C.

1975-01-01

230

Naturally occurring glucosinolates in plant extracts of rocket salad (Eruca sativa L.) identified by liquid chromatography coupled with negative ion electrospray ionization and quadrupole ion-trap mass spectrometry.  

PubMed

A method for the comprehensive profiling of intact glucosinolates (GLSs), major and minor, occurring in leaves and seeds of rocket salad (Eruca sativa L.) is presented using optimized reversed-phase liquid chromatography (RP-LC) with electrospray ionization (ESI) ion trap mass spectrometry (ITMS). ESI-ITMS in the negative mode was confirmed to be very suitable to analyze these compounds in crude extracts. After extraction from the plant material with methanol/water (70:30 v/v) at 70 degrees C, the analytes of interest were separated on a C18 column using an eluent acidified with formic acid (0.1%) and modified with acetonitrile. All the GLSs found in leaves of rocket salad gave good signals corresponding to the deprotonated precursor ion, [M-H]-. Although the mass spectra also exhibited an analytically important non-covalent adduct ion at [2M-H]-, the structures of glucosinolates were confirmed by extensive sequential MS analysis, thereby substantially improving the identification of unknown compounds. The results obtained not only revealed in leaves of E. sativa at least twelve species of GLSs including seven aliphatic compounds (glucoraphanin with [M-H]- at m/z ratio of 436, glucoerucin at m/z 420, 4-mercaptobutyl-GLS at m/z 406, progoitrin/epiprogoitrin at m/z 388, sinigrin at m/z 358, 4-methylpentyl- and n-hexyl-GLS at m/z 402) and three indole glucosinolates (i.e., three N-heterocyclic compounds: 4-hydroxyglucobrassicin and 5-hydroxyglucobrassicin at m/z 463, and 4-methoxy-glucobrassicin at m/z 477), but also two structurally related compounds containing one intermolecular disulfide linkage (4-(beta-D-glucopyranosyldisulfanyl)butyl-GLS at m/z 600 and a dimeric 4-mercaptobutyl-GLS at m/z 811). This latter symmetric disulfide was previously considered as an artefact formed during extraction of GLSs from vegetative tissues. Glucosinolates were detected in the leaves with a wide range of contents (10-200 micromol/g) and a great variation in the composition. Only three GLSs were identified in seeds of rocket salad, namely glucoraphanin, glucoerucin and 4-methoxyglucobrassicin. As expected, the most abundant GLS in seeds is glucoerucin. The feasibility of the strategy was also demonstrated using a rapeseed extract of certified reference material (BCR367R). The results indicated the usefulness of this method for a rapid, sensitive and comprehensive profiling of the GLS family naturally occurring in extracts of crude plant matter. PMID:17590871

Cataldi, Tommaso R I; Rubino, Alessandra; Lelario, Filomena; Bufo, Sabino A

2007-01-01

231

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

232

Screening and quantification of pesticide residues in fruits and vegetables making use of gas chromatography-quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization.  

PubMed

An atmospheric pressure chemical ionization source has been used to enhance the potential of gas chromatography coupled with quadrupole time-of-flight (QTOF) mass spectrometry (MS) for screening and quantification purposes in pesticide residue analysis. A screening method developed in our laboratory for around 130 pesticides has been applied to fruit and vegetable samples, including strawberries, oranges, apples, carrots, lettuces, courgettes, red peppers, and tomatoes. Samples were analyzed together with quality control samples (at 0.05 mg/kg) for each matrix and for matrix-matched calibration standards. The screening strategy consisted in first rapid searching and detection, and then a refined identification step using the QTOF capabilities (MS(E) and accurate mass). Identification was based on the presence of one characteristic m/z ion (Q) obtained with the low collision energy function and at least one fragment ion (q) obtained with the high collision energy function, both with mass errors of less than 5 ppm, and an ion intensity ratio (q/Q) within the tolerances permitted. Following this strategy, 15 of 130 pesticides were identified in the samples. Afterwards, the quantitation capabilities were tested by performing a quantitative validation for those pesticides detected in the samples. To this aim, five matrices were selected (orange, apple, tomato, lettuce, and carrot) and spiked at two concentrations (0.01 and 0.1 mg/kg), and quantification was done using matrix-matched calibration standards (relative responses versus triphenyl phosphate used as an internal standard). Acceptable average recoveries and relative standard deviations were obtained for many but not all pesticide-matrix combinations. These figures allowed us to perform a retrospective quantification of positives found in the screening without the need for additional analysis. Taking advantage of the accurate-mass full-spectrum data provided by QTOF MS, we searched for a higher number of compounds (up to 416 pesticides) in a second stage by performing extra data processing without any new sample injection. Several more pesticides were detected, confirmed, and/or tentatively identified when the reference standard was unavailable, illustrating in this way the potential of gas chromatography-QTOF MS to detect pesticides in addition to the ones targeted in quantitative analysis of pesticides in food matrices. PMID:24828980

Cervera, M I; Portolés, T; López, F J; Beltrán, J; Hernández, F

2014-11-01

233

Laser diode thermal desorption atmospheric pressure chemical ionization tandem mass spectrometry applied for the ultra-fast quantitative analysis of BKM120 in human plasma.  

PubMed

A sensitive and ultra-fast method utilizing the laser diode thermal desorption ion source using atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS) was developed for the quantitative analysis of BKM120, an investigational anticancer drug in human plasma. Samples originating from protein precipitation (PP) followed by salting-out assisted liquid-liquid extraction (SALLE) were spotted onto the LazWell™ plate prior to their thermal desorption and detection by tandem mass spectrometry in positive mode. The validated method described in this paper presents a high absolute extraction recovery (>90 %) for BKM120 and its internal standard (ISTD) [D8]BKM120, with precision and accuracy meeting the acceptance criteria. Standard curves were linear over the range of 5.00 to 2000 ng mL(-1) with a coefficient of determination (R (2)) >0.995. The method specificity was demonstrated in six different batches of human plasma. Intra- and inter-run precision as well as accuracy within ±20 % at the lower limit of quantification (LLOQ) and ±15 % (other levels) were achieved during a three-run validation for quality control (QC) samples. The post-preparative stability on the LazWell™ plate at room temperature was 72 h and a 200-fold dilution of spiked samples was demonstrated. The method was applied successfully to three clinical studies (n?=?847) and cross-checked with the validated LC-ESI-MS/MS reference method. The sample analysis run time was 10 s as compared to 4.5 min for the current validated LC-ESI-MS/MS method. The resultant data were in agreement with the results obtained using the validated reference LC-ESI-MS/MS assay and the same pharmacokinetic (PK) parameters were calculated for both analytical assays. This work demonstrates that LDTD-APCI-MS/MS is a reliable method for the ultra-fast quantitative analysis of BKM120 which can be used to speed-up and support its bioanalysis in the frame of the clinical trials. PMID:24958346

Lanshoeft, Christian; Heudi, Olivier; Leuthold, Luc Alexis; Schlotterbeck, Götz; Elbast, Walid; Picard, Franck; Kretz, Olivier

2014-09-01

234

Ionizing radiation  

NASA Technical Reports Server (NTRS)

The biological effects of ionizing radiation encountered in space are considered. Biological experiments conducted in space and some experiences of astronauts during space flight are described. The effects of various levels of radiation exposure and the determination of permissible dosages are discussed.

Tobias, C. A.; Grigoryev, Y. G.

1975-01-01

235

Novel physico-chemical diagnostic tools for high throughput identification of bovine mastitis associated gram-positive, catalase-negative cocci  

PubMed Central

Background The routine diagnosis of Streptococcus spp. and other mastitis associated gram-positive, catalase-negative cocci is still based upon biochemical tests and serological methods, which frequently provide ambiguous identification results. We therefore aimed to establish an accurate identification system for differential diagnosis of mastitis associated Streptococcus spp. and related species using biophysical techniques such as Fourier-transform infrared (FTIR) spectroscopy and MALDI – TOF/MS. Results Based on a panel of 210 isolates from cases of bovine mastitis, an unsupervised FTIR spectral reference library was established and an artificial neural network (ANN) - assisted identification system was developed. All bacterial isolates were previously identified by species-specific PCR and/or 16S rRNA gene sequence analysis. An overall identification rate of 100% at species level for 173 strains unknown to the ANN and the library was achieved by combining ANN and the spectral database, thus demonstrating the suitability of our FTIR identification system for routine diagnosis. In addition, we investigated the potential of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of mastitis associated Streptococcus spp. and related bacteria. Using the Microflex LT System, MALDI Biotyper software™ (V3.3) we achieved an accuracy rate of 95.2%. A blind study, including 21 clinical samples from dairy cows, revealed a 100% correct species identification rate for FTIR and 90.5% for MALDI-TOF MS, indicating that these techniques are valuable tools for diagnosis. Conclusions This study clearly demonstrates that FTIR spectroscopy as well as MALDI-TOF MS can significantly improve and facilitate the identification and differentiation of mastitis associated Streptococcus spp. and related species. Although the FTIR identification system turned out being slightly superior to MALDI-TOF MS in terms of identification on species level, both methods offer interesting alternatives to conventional methods currently used in mastitis diagnosis as both of them provide high accuracy at low operating costs once the instrument is acquired. PMID:25015262

2014-01-01

236

Negative Leadership.  

National Technical Information Service (NTIS)

Senior leaders must have the moral courage to modify the behavior or eliminate negative leadership in the Army. If action is not taken immediately, negative leaders and their toxic leadership style will be taught to their subordinates, the future leaders ...

D. M. Oberlander

2013-01-01

237

Average local ionization energy generalized to correlated wavefunctions  

NASA Astrophysics Data System (ADS)

The average local ionization energy function introduced by Politzer and co-workers [Can. J. Chem. 68, 1440 (1990)] as a descriptor of chemical reactivity has a limited utility because it is defined only for one-determinantal self-consistent-field methods such as the Hartree-Fock theory and the Kohn-Sham density-functional scheme. We reinterpret the negative of the average local ionization energy as the average total energy of an electron at a given point and, by rewriting this quantity in terms of reduced density matrices, arrive at its natural generalization to correlated wavefunctions. The generalized average local electron energy turns out to be the diagonal part of the coordinate representation of the generalized Fock operator divided by the electron density; it reduces to the original definition in terms of canonical orbitals and their eigenvalues for one-determinantal wavefunctions. The discussion is illustrated with calculations on selected atoms and molecules at various levels of theory.

Ryabinkin, Ilya G.; Staroverov, Viktor N.

2014-08-01

238

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

239

Novel two-step laser ablation and ionization mass spectrometry (2S-LAIMS) of actor-spectator ice layers: probing chemical composition of D2O ice beneath a H2O ice layer.  

PubMed

In this work, we report for the first time successful analysis of organic aromatic analytes imbedded in D2O ices by novel infrared (IR) laser ablation of a layered non-absorbing D2O ice (spectator) containing the analytes and an ablation-active IR-absorbing H2O 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 H2O ice layer (actor) generates a shockwave upon impact. This shockwave penetrates the lower analyte-containing D2O 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 D2O 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 H2O 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. PMID:24628162

Yang, Rui; Gudipati, Murthy S

2014-03-14

240

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

241

Pulsed discharge helium ionization detector  

Microsoft Academic Search

A pulsed discharge helium ionization detector (PDHID) (patent pending) for gas chromatography has been developed. This detector uses a non-radioactive pulsed high voltage discharge source for generation of electrons and pulsed collection of these electrons. We have evaluated this detector for the analysis of a wide range of chemical compounds. In this paper the analytes are passed through the discharge

W. E. Wentworth; S. V. Vasnin; S. D. Stearns; C. J. Meyer

1992-01-01

242

Molecular Hydrogen in the Ionized Region of Planetary Nebulae  

Microsoft Academic Search

This paper presents an analysis of the concentration of hydrogen molecules inside the ionized region of planetary nebulae (PNs). The equations corresponding to the ionization and chemical equilibria of H, H+, H-, H2, H+2, and H+3 are coupled with the equations of ionization and thermal balance for a photoionized atomic gas. A total of 40 different reactions related to the

Isabel Aleman; Ruth Gruenwald

2004-01-01

243

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

244

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

245

Real-time flavor analysis: optimization of a proton-transfer-mass spectrometer and comparison with an atmospheric pressure chemical ionization mass spectrometer with an MS-nose interface.  

PubMed

Two techniques are recognized for the real-time analysis of flavors during eating and drinking, atmospheric pressure chemical ionization mass spectrometry (APCI-MS), and proton transfer reaction mass spectrometry (PTR-MS). APCI-MS was developed for the analysis of flavors and fragrances, whereas PTR-MS was originally developed and optimized for the analysis of atmospheric pollutants. Here, the suitability of the two techniques for real-time flavor analysis is compared, using a varied range of common flavor compounds. An Ionicon PTR-MS was first optimized and then its performance critically compared with that of APCI-MS. Performance was gauged using the capacity for soft ionization, dynamic linear range, and limit of detection. Optimization of the PTR-MS increased the average sensitivity by a factor of more than 3. However, even with this increase in sensitivity, the Limit of Detection was typically 10 times higher and the Dynamic Linear Range ten times narrower than that of the APCI-MS. PMID:23394597

Avison, Shane J

2013-03-01

246

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

247

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

248

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

249

Simultaneous measurements of peroxyacetyl nitrate and peroxyacetic acid by Chemical Ionization Mass Spectrometry (CIMS): contrasting boreal forest with rural continental Europe  

NASA Astrophysics Data System (ADS)

The peroxyacetyl radical (PA) is formed via the photochemical oxidation of a number of different VOCs. PA radical acts as the source of peroxyacetyl nitrate (PAN), via the reaction with NO2, and peroxyacetic acid (PAA), via reaction with the HO2 radical. PAN can act as a temporary reservoir of both PA radical and NO2 transporting NOx far from source regions, whereas PAA lifetimes, dominated by deposition, are shorter. We present simultaneous measurements of PAN and PAA in different environments and study the chemistry of the PA radical in contrasting chemical and meteorological conditions. PAN and PAA were measured simultaneously using CIMS during two field intensives with contrasting meteorological and chemical conditions. The HUMPPA-COPEC 2010 campaign took place during July-August 2010 at the SMEAR II field site, located in boreal forest near Hyytiälä, Finland [1]. The campaign was characterised by above average temperatures with large emissions of BVOCs from the boreal forest. The Particles and Radicals: Diel observations of the impact of urban and biogenic Emissions (PARADE) campaign took place during August-September 2011 at the mountaintop fieldsite on the Kleiner Feldberg, Hessen, Germany, approximately 10 km north of Frankfurt. Temperatures were markedly lower during PARADE compared to HUMPPA and the site had much lower impact from VOCs and a much larger impact from anthropogenic emissions. PAA was found to be a large proportion of ?PA(PAA+PAN) during the HUMPPA campaign, approaching 50% on occasion. In addition, PAA was found to make up a significant fraction of the total organic peroxides. In contrast, ?PA(PAA+PAN)during PARADE was dominated by PAN reflecting the lower temperatures and NOx levels. [1] J. Williams et al, 2011, Atmos. Chem. Phys., 11, 10599-10618

Phillips, G. J.; Pouvesle, N.; Thieser, J.; Axinte, R.; Schuster, G.; Fischer, H.; Williams, J.; Crowley, J. N.

2012-04-01

250

Carbon nanodots as a matrix for the analysis of low-molecular-weight molecules in both positive- and negative-ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and quantification of glucose and uric acid in real samples.  

PubMed

Carbon nanodots were applied for the first time as a new matrix for the analysis of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in both positive- and negative-ion modes. A wide range of small molecules including amino acids, peptides, fatty acids, as well as ?-agonists and neutral oligosaccharides were analyzed by MALDI MS with carbon nanodots as the matrix, and the lowest 0.2 fmol limits-of-detection were obtained for octadecanoic acid. Clear sodium and potassium adducts and deprotonated signals were produced in positive- and negative-ion modes. Furthermore, the glucose and uric acid in real samples were quantitatively determined by the internal standard method with the linear range of 0.5-9 mM and 0.1-1.8 mM (R(2) > 0.999), respectively. This work gives new insight into the application of carbon nanodots and provides a general approach for rapid analysis of low-molecular-weight compounds. PMID:23796018

Chen, Suming; Zheng, Huzhi; Wang, Jianing; Hou, Jian; He, Qing; Liu, Huihui; Xiong, Caiqiao; Kong, Xianglei; Nie, Zongxiu

2013-07-16

251

Chemical mutagenesis testing in Drosophila. I. Comparison of positive and negative control data for sex-linked recessive lethal mutations and reciprocal translocations in three laboratories  

SciTech Connect

As part of the validation phase of the Drosophila melanogaster segment of the National Toxicology Program, a comparison has been made of positive and negative controls for sex-linked recessive lethal mutations and reciprocal translocations from three laboratories. This comparison involves approximately 700,000 spontaneous recessive lethal mutation tests, 70,000 spontaneous translocation tests, and screens for genetic damage induced by N-nitrosodimethylamine and ..beta..-propiolactone. Spontaneous frequencies for lethal mutations and translocations were homogeneous in the laboratories regardless of solvent or broods sampled. Inhomogeneity was observed in induced frequencies among laboratories, but the variation was no greater than that found within a laboratory.

Woodruff, R.C.; Mason, J.M.; Valencia, R.; Zimmering, S.

1984-01-01

252

Effects of drying control chemical additive on properties of Li 4Ti 5O 12 negative powders prepared by spray pyrolysis  

Microsoft Academic Search

High-density Li4Ti5O12 powders comprising spherical particles are prepared by spray pyrolysis from a solution containing dimethylacetamide (drying control chemical additive) and citric acid and ethylene glycol (organic additives). The prepared powders have high discharge capacities and good cycle properties. The optimum concentration of dimethylacetamide is 0.5M. The addition of dimethylacetamide to the polymeric spray solutions containing citric acid and ethylene

Seo Hee Ju; Yun Chan Kang

2010-01-01

253

Ionization Energies of Lanthanides  

ERIC Educational Resources Information Center

This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above…

Lang, Peter F.; Smith, Barry C.

2010-01-01

254

Development of a liquid chromatography-electrospray chemical ionization tandem mass spectrometry analytical method for analysis of eleven hydroxylated polybrominated diphenyl ethers.  

PubMed

Recently, hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have emerged as environmentally relevant pollutants due to recent reports of their natural production and metabolism. Recent mechanistic studies in human and rats have shown that some OH-PBDEs are more potent than parent compounds (PBDEs) and may contribute substantially to neurodevelopmental disorders by direct neurotoxicity, or indirectly through altered thyroid disruption. However, analytical methodologies for determination of OH-PBDEs are currently limited. In this study a robust liquid chromatography-electrospray tandem triple quadrupole-linear ion trap mass spectrometer (LC-ESI-QqLIT-MS-MS) in negative mode method was developed for the determination of eleven OH-tri- to OH-hexa-PBDEs. Two different columns were tested and compared for chromatographic separation: a C18 BetaBasic and a Purospher STAR RP 18, working at pH 8 and 10, respectively. Mobile phase (acetonitrile:water) was optimized by changing the pH of the aqueous phase and the concentration of the organic modifier (methanol). The MS-MS parameters (declustering potential (DP), collision energy (CE) and cell exit potential (CXP)) were optimized. Selected reaction monitoring (SRM) was used in order to increase sensitivity. Two SRM transitions ([M-H](-)>[Br](-)) were selected for each OH-PBDE, one for quantification and the second one for confirmation. Under the optimized conditions, the instrumental limits of detection were between 0.17 and 0.72injectedpg. The method provided good linearity (r>0.99 for a concentration range of 0.30-100ng/mL), accuracy and precision (%Dev and %RSD?20% for intra- and inter-assays). PMID:23791149

Feo, Maria Luisa; Barón, Enrique; Aga, Diana S; Eljarrat, Ethel; Barceló, Damià

2013-08-01

255

Lymphoblastoid lines and skin fibroblasts from patients with tuberous sclerosis are abnormally sensitive to ionizing radiation and to a radiomimetic chemical  

SciTech Connect

Lymphoblastoid lines, derived by transforming peripheral blood lymphocytes with Epstein-Barr virus, and skin fibroblast lines were established from two patients with tuberous sclerosis. The number of viable lymphoblastoid cells was determined by their ability to exclude the vital dye trypan blue after their irradiation with x-rays or 254 nm ultraviolet light. The growth of fibroblasts was determined by their ability to form colonies after treatment with the radiomimetic, DNA-damaging chemical N-methyl-N'-nitro-N-nitrosoguanidine. The tuberous sclerosis lymphoblastoid lines were hypersensitive to x-rays but had normal sensitivity to the ultraviolet radiation. The tuberous sclerosis fibroblast lines were hypersensitive to the N-methyl-N'-nitro-N-nitrosoguanidine. The hypersensitivity of tuberous sclerosis cells to x-rays and to N-methyl-N'-nitro-N-nitrosoguanidine is believed to reflect defective repair of DNA damaged by these agents and may provide the basis for in vitro, including prenatal, diagnostic tests for tuberous sclerosis.

Scudiero, D.A.; Moshell, A.N.; Scarpinato, R.G.; Meyer, S.A.; Clatterbuck, B.E.; Tarone, R.E.; Robbins, J.H.

1982-03-01

256

Matrix isolation studies of the interactions of BF3 with water and substituted diethyl ethers. Chemical ionization mass spectrometric determination of the proton affinity of (CF3CH2)2O  

NASA Technical Reports Server (NTRS)

BF3 was co-condensed with H2O, D2O, (C2H5)2O, (CF3CH2)2O, and (C2F5)2O in excess argon at 15 K. Infrared spectra of BF3/water isolated in solid argon provided a more complete analysis of the BF3--H2O complex than previously published. Infrared spectra of the matrices showed a definite Lewis acid-base interaction between BF3 and diethyl ether; a weak but definite interaction with bis (2,2,2-trifluorodiethyl) ether, and no observable interaction with perfluorodiethyl ether. Thus, the ether data indicate a clear trend between strength of interaction with BF3 and the degree of F substitution. To support and explain the emerging relationship between interaction strength and the basicity of the oxygen-containing molecule, the proton affinity of (CF3CH2)2O was measured using chemical ionization mass spectrometry. The implications of the results for lubricant/metal oxide surface interactions are discussed.

Ball, David W.; Zehe, Michael J.

1993-01-01

257

Study of three-dimensional configurations of (?-methacryloxypropyl)-silsesquioxanes by ultraviolet laser matrix-assisted desorption/ionization time-of-flight mass spectrometry and quantum chemical calculation.  

PubMed

[(3-Methacryloxy)propyl]silsesquioxanes (MSSO) were prepared from the hydrolytic condensation of [(3-methacryloxy)-propyl]trimethoxysilane (MPMS) in the presence of an acid catalyst (HCOOH). The proposed MSSO structures were characterized with Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) ((1)H, (13)C and (29)Si), and were assigned by ultraviolet laser matrix-assisted desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS). The large organic group connected to silicon was simplified for the quantum chemical calculation (QCC), and the correlation of the calculated total energies (E(T)) before and after simplification was analyzed by multiple linear regression, verifying no significant influence on the final conclusions of the research of structural formulas by a correlation coefficient (r). The geometric parameters (Si-O bond length and Si-O-Si, O-Si-O bond angles) and E(T) of the simplified MSSO were calculated by QCC to determine the relative stability of various MSSO structures. The structural geometry (silicon ring), the fraction of intramolecular cycles (f) and the number of the silicon rings (F) were also employed to qualitatively determine the relative stability. The results of the calculation showed that almost all of the cage structures had a lower E(T) than the isomeric ladder structures; therefore, most MSSO structures are of the cage type. PMID:21594941

Wang, Di; You, Hong; Hu, Lijiang

2011-06-15

258

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

259

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 ...

260

Negative thermal ion mass spectrometry of osmium, rhenium, and iridium  

SciTech Connect

The authors report on a technique for obtaining intense ion beams of negatively charged oxides of Os, Re, and Ir by thermal ionization, in a conventional surface ionization mass spectrometer. It was found that the principal ion species of Os, Re, and Ir produced are OsO{sub 3}{sup {minus}}, ReO{sub 4}{sup {minus}}, and IrO{sub 2}{sup {minus}}. The sharp distinction in the masses of the dominant molecular species produced by this technique permits the measurement of isotopic compositions of each element from mixtures of platinum-group elements without significant isobaric interferences. For {sup 187}Re-{sup 187}Os isotope studies, this technique offers the advantage of isotopic analyses without prior chemical separation of Re from Os, as no isobaric interference between the oxides of {sup 187}Os and {sup 187}Re exists under these conditions. For 4 ng Os, stable ion currents of 3 {times} 10{sup {minus}12} A can be maintained for over one hour, which allows determination of isotopic ratios with a Faraday collector to a precision of better than {plus minus}2{per thousand} (2 {sigma}{sub m}). For 70 pg Os, isotopic ratios can be measured with a precision of better than {plus minus}5{per thousand} using a secondary electron multiplier. The detection limit for Os is estimated to be below 10{sup {minus}14} g. Osmium isotopic ratios have also been determined by direct loading of natural iridosmine with a precision of {plus minus}0.5{per thousand} or better. They have obtained ionization efficiencies of 2-6% for Os and >20% for Re; these are superior to those reported for other techniques available to data, and demonstrate that negative thermal ion mass spectrometry will have widespread application to {sup 187}Re-{sup 187}Os chronometry and to studies of the geochemistry and environmental chemistry of the platinum-group elements.

Creaser, R.A.; Papanastassiou, D.A.; Wasserburg, G.J. (California Institute of Technology, Pasadena (USA))

1991-01-01

261

New quantitative structure-fragmentation relationship strategy for chemical structure identification using the calculated enthalpy of formation as a descriptor for the fragments produced in electron ionization mass spectrometry: a case study with tetrachlorinated biphenyls.  

PubMed

Differential mass spectrometry correlated with quantum chemical calculations (QCC-?MS) has been shown to be an efficient tool for the chemical structure identification (CSI) of isomers with similar mass spectra. For this type of analysis, we report here a new strategy based on ordering (ORD), linear correlation (LCOR) algorithms, and their coupling, to filter the most probable structures corresponding to similar mass spectra belonging to a group with dozens of isomers (e.g., tetrachlorinated biphenyls, TeCBs). This strategy quantifies and compares the values of enthalpies of formation (?(f)H) obtained by QCC for some isobaric ions from the electron ionization (EI)-MS mass spectra, to the corresponding relative intensities. The result of CSI is provided in the form of lists of decreasing probabilities calculated for all the position-isomeric structures using the specialized software package CSI-Diff-MS Analysis 3.1.1. The simulation of CSI with ORD, LCOR, and their coupling of six TeCBs (IUPAC no. 44, 46, 52, 66, 74, and 77) has allowed us to find the best semiempirical molecular-orbital methods for several of their common isobaric fragments. The study of algorithms and strategy for the entire group of TeCBs (42 isomers) was made with one of the optimal variants for the computation of ?(f)H using semiempirical molecular orbital methods of HyperChem: AM1 for M(+•) and [M - 4Cl](+•) ions and RM1 for [M - Cl](+) and [M - 2Cl](+•). The analytical performance of ORD, LCOR, and their coupling resulted from the CSI simulation of an analyte of known structure, using a decreasing number of isomeric standards, s = 5, 4, 3, and 2. Compared with the results obtained by a classical library search for TeCB isomers, the novel strategies of assigning structures of isomers with very similar mass spectra based on ORD, LCOR, and their coupling were much more efficient, because they provide the correct structure at the top of the probability list. Databases used in these CSI do not contain mass spectra, as in the case of a library search, but a series of ?(f)H values obtained by QCC. These techniques are capable of relating relative intensities to the chemical structures of analytes via ?(f)H of ions which turns out to be a good quantitative structure-fragmentation relationship (QSFR) descriptor. PMID:24773183

Dinca, Nicolae; Dragan, Simona; Dinca, Mihael; Sisu, Eugen; Covaci, Adrian

2014-05-20

262

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

263

Negativity Bias, Negativity Dominance, and Contagion  

Microsoft Academic Search

We hypothesize that there is a general bias, based on both innate predispositions and experience, in animals and humans, to give greater weight to negative entities (e.g., events, objects, personal traits). This is manifested in 4 ways: (a) negative potency (negative entities are stronger than the equivalent positive entities), (b) steeper nega - tive gradients (the negativity of negative events

Paul Rozin; Edward B. Royzman

2001-01-01

264

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

265

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...

266

IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. V. ALFVÉN IONIZATION  

SciTech Connect

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{sup –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{sup –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, H{sub 2}, 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.; Rimmer, P. B. [SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, KY16 9SS (United Kingdom); Diver, D. A., E-mail: craig.stark@st-andrews.ac.uk [SUPA, School of Physics and Astronomy, Kelvin Building, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)

2013-10-10

267

Screening, library-assisted identification and validated quantification of 23 benzodiazepines, flumazenil, zaleplone, zolpidem and zopiclone in plasma by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization.  

PubMed

A liquid chromatographic/mass spectrometric assay with atmospheric pressure chemical ionization (LC/APCI-MS) is presented for fast and reliable screening and identification and also for precise and sensitive quantification in plasma of the 23 benzodiazepines alprazolam, bromazepam, brotizolam, camazepam, chlordiazepoxide, clobazam, clonazepam, diazepam, flunitrazepam, flurazepam, desalkylflurazepam, lorazepam, lormetazepam, medazepam, metaclazepam, midazolam, nitrazepam, nordazepam, oxazepam, prazepam, temazepam and tetrazepam, triazolam, their antagonist flumazenil and the benzodiazepine BZ1 (omega 1) receptor agonists zaleplone, zolpidem and zopiclone. It allows confirmation of the diagnosis of an overdose situation and monitoring of psychiatric patients' compliance. The analytes were isolated from plasma using liquid-liquid extraction and were separated on a Merck LiChroCART column with Superspher 60 RP Select B as the stationary phase. Gradient elution was performed using aqueous ammonium formate and acetonitrile. After screening and identification in the scan mode using the authors' LC/MS library, the analytes were quantified in the selected-ion monitoring mode. The quantification assay was fully validated. It was found to be selective proved to be linear from sub-therapeutic to over therapeutic concentrations for all analytes, except bromazepam. The corresponding reference levels the assay's accuracy and precision data for all studied substances are listed. The accuracy and precision data were within the required limits with the exception of those for bromazepam. The analytes were stable in frozen plasma for at least 1 month. The validated assay was successfully applied to several authentic plasma samples from patients treated or intoxicated with various benzodiazepines or with zaleplone, zolpidem or zopiclone. It has proven to be appropriate for the isolation, separation, screening, identification and quantification of the drugs mentioned above in plasma for clinical toxicology, e.g. in cases of poisoning, and forensic toxicology, e.g. in cases of driving under the influence of drugs. PMID:15329838

Kratzsch, Carsten; Tenberken, Oliver; Peters, Frank T; Weber, Armin A; Kraemer, Thomas; Maurer, Hans H

2004-08-01

268

A novel derivatization method for the determination of Fosfomycin in human plasma by liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection via phase transfer catalyzed derivatization.  

PubMed

An analytical method employing novel sample preparation and liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection (LC-APCI/MS) was developed for the determination of fosfomycin in human plasma. Sample preparation involves derivatization through phase transfer catalysis (PTC) which offers multiple advantages due to the simultaneous extraction, preconcentration and derivatization of the analyte. Using a PT catalyst, fosfomycin was extracted from plasma in an organic phase and, then converted to a pentafluorobenzyl ester with the use of pentafluorobenzyl bromide (PFBBr) derivatization reagent. The method was fully optimized by taking into account both PTC and derivatization parameters. Several catalysts, in a wide range of concentrations, with different counter ions and polarities were tested along with different extraction solvents and pH values. Thereafter, the derivatization procedure was optimized by altering the amount of the derivatization reagent, the temperature of the reaction and finally, the derivatization duration. As internal standard (I.S.) ethylphosphonic acid was chosen and underwent the same pretreatment. The derivatives were separated on a pentafluorophenyl (PFP)-C18 analytical column, which provides unique selectivity, using an isocratic elution with acetonitrile-water (70-30, v/v). The method was validated according to US Food and Drug Administration (FDA) guidelines and can be used for a bioequivalence study of fosfomycin in human plasma. The correlation coefficient (r(2)) of the calibration curve of spiked plasma solutions in the range of 50-12000 ng/mL was found greater than 0.999 with a limit of quantitation (LOQ) equal to 50 ng/ml (for 500 ?L plasma sample). PMID:24508398

Papakondyli, Theodora A; Gremilogianni, Aikaterini M; Megoulas, Nikolaos C; Koupparis, Michael A

2014-03-01

269

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

270

An improved dispersive solid-phase extraction clean-up method for the gas chromatography-negative chemical ionisation tandem mass spectrometric determination of multiclass pesticide residues in edible oils.  

PubMed

An improved sample preparation using dispersive solid-phase extraction clean-up was proposed for the trace level determination of 35 multiclass pesticide residues (organochlorine, organophosphorus and synthetic pyrethroids) in edible oils. Quantification of the analytes was carried out by gas chromatography-mass spectrometry in negative chemical ionisation mode (GC-NCI-MS/MS). The limit of detection and limit of quantification of residues were in the range of 0.01-1ng/g and 0.05-2ng/g, respectively. The analytes showed recoveries between 62% and 110%, and the matrix effect was observed to be less than 25% for most of the pesticides. Crude edible oil samples showed endosulfan isomers, p,p'-DDD, ?-cypermethrin, chlorpyrifos, and diazinon residues in the range of 0.56-2.14ng/g. However, no pesticide residues in the detection range of the method were observed in refined oils. PMID:24001824

Deme, Pragney; Azmeera, Tirupathi; Prabhavathi Devi, B L A; Jonnalagadda, Padmaja R; Prasad, R B N; Vijaya Sarathi, U V R

2014-01-01

271

An isomer-specific high-energy collision-induced dissociation MS/MS database for forensic applications: a proof-of-concept on chemical warfare agent markers.  

PubMed

Spectra database search has become the most popular technique for the identification of unknown chemicals, minimizing the need for authentic reference chemicals. In the present study, an isomer-specific high-energy collision-induced dissociation (CID) MS/MS spectra database of 12 isomeric O-hexyl methylphosphonic acids (degradation markers of nerve agents) was created. Phosphonate anions were produced by the electrospray ionization of phosphonic acids or negative-ion chemical ionization of their fluorinated derivatives and were analysed in a hybrid magnetic-sector-time-of-flight tandem mass spectrometer. A centre-of-mass energy (E(com)) of 65?eV led to an optimal sequential carbon-carbon bond breakage, which was interpreted in terms of charge remote fragmentation. The proposed mechanism is discussed in comparison with the routinely used low-energy CID MS/MS. Even-mass (odd-electron) charge remote fragmentation ion series were diagnostic of the O-alkyl chain structure and can be used to interpret unknown spectra. Together with the odd-mass ion series, they formed highly reproducible, isomer-specific spectra that gave significantly higher database matches and probability factors (by 1.5 times) than did the EI MS spectra of the trimethylsilyl derivatives of the same isomers. In addition, ionization by negative-ion chemical ionization and electrospray ionization resulted in similar spectra, which further highlights the general potential of the high-energy CID MS/MS technique. PMID:21915956

Subramaniam, Raja; Östin, Anders; Nygren, Yvonne; Juhlin, Lars; Nilsson, Calle; Åstot, Crister

2011-09-01

272

IMPROVED CHEMISTRY MODELS FOR DSMC SIMULATIONS OF IONIZED RAREFIED HYPERSONIC FLOWS.  

E-print Network

??This thesis describes research in modeling rarefied, nonequilibrium hypersonic flows using the direct simulation Monte Carlo (DSMC) method. Modeling of chemical reactions and ionization processes… (more)

Ozawa, Takashi

2007-01-01

273

Capillary gas chromatography with chemical ionization negative ion mass spectrometry in the identification of odorous steroids formed in metabolic studies of the sulphates of androsterone, DHA and 5?-androst-16-en-3?-ol with human axillary bacterial isolates  

Microsoft Academic Search

The products of metabolism of the sulphates (0.5 ?mol\\/l) of androsterone, dehydroepiandrosterone (DHA) and 5?-androst-16-en-3?-ol have been investigated after incubation with 72 h cultures of human axillary bacterial isolates for 3 days at 37°C. The medium used, tryptone soya broth (TSB), contained yeast extract and Tween 80. The isolates used were Coryneform F1 (known previously to metabolize testosterone and to

D. B. Gower; A. I. Mallet; W. J. Watkins; L. M. Wallace; J.-P. Calame

1997-01-01

274

QUANTITATION OF ESTROGENS IN GROUND WATER AND SWINE LAGOON SAMPLE USING SOLID PHASE EXTRACTION, PENTAFLUROBENZYL/TRIMETHYLSILYL DERIVATIZATIONS AND GAS CHROMATOGRAPHY NEGATIVE ION CHEMICAL IONIZATION/MASS SPECTROMETRY/MASS SPECTROMETRY  

EPA Science Inventory

A method was developed for the confirmed identification and quantitation of 17B-estradiol, estrone, 17B-ethynylestrodial and 16a-hydroxy-17B-estradiol (estriol) in ground water and swine lagoon samples. Centrifuged and filtered samples were extracted using solid phase extraction...

275

Drug Testing in Blood: Validated Negative-Ion Chemical Ionization Gas Chromatographic-Mass Spectrometric Assay for Determination of Amphetamine and Methamphetamine Enantiomers and Its Application to Toxicology Cases  

Microsoft Academic Search

Background: Enantioselective analysis of amphetamine (AM) or methamphetamine (MA) in urine is already a well-established tool for differentiation of illicit from therapeutic ingestion of AM or MA derivatives. How- ever, because of the increasing importance of plasma or serum in analytical toxicology, a method for enantiose- lective analysis of AM and MA in these matrices is needed. Methods: AM and\\/or

Frank T. Peters; Thomas Kraemer; Hans H. Maurer

276

Kinetics of the reactions of acetone and glyoxal with O2+ and NO+ ions and application to the detection of oxygenated volatile organic compounds in the atmosphere by chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

In situ measurements of oxygenated volatile organic compounds (OVOC) in the upper troposphere-lower stratosphere (UTLS) have gained strong interest because these compounds may be transported during convective events to the UTLS, where they may contribute to the HOx budget thus influencing the chemistry of ozone. With the aim to quantify OVOC of similar mass (58 u) by chemical ionization mass spectrometry (CIMS), ion-molecule reactions of acetone and glyoxal with O2+ and NO+ have been studied. O2+ reacts at the theoretical collision rate with acetone and glyoxal, with room-temperature rate constant values of (3.1 ± 0.7) × 10-9 and (1.8 ± 0.4) × 10-9 cm3 molecule-1 s-1, respectively, independent of pressure. The charge transfer product ion (m/z 58) and a specific fragment product ion are formed for each reaction. NO+ reacts with acetone and glyoxal with a rate constant lower than the collision rate in N2 buffer gas at 1.7 hPa, leading to the formation of the association product in both cases as single reaction productE The rate constants increase with pressure at 295 K for both ranges of 1.2-19.2 hPa N2 and 1.3-2.6 hPa He, indicating a falloff kinetic regime. These results are analysed using conventional statistical calculations. Consistency of the rate constants is obtained for both buffer gases and pressure ranges employed, and high-pressure limits are in agreement with the collision rate constants. Troe analytical expressions of the rate constants are derived for use under any pressure and temperature. From the reaction kinetics and mechanisms obtained in this study and others, a scheme is discussed to quantify separately acetone, glyoxal, and propanal in the UTLS by CIMS, using NO+, O2+, and H3O+ as reagent ions, taking into account potential interferences from other important OVOC such as acetaldehyde and from non-methane hydrocarbons such as n-propane, butane and 2-methyl propane.

Guimbaud, C.; Catoire, V.; Bergeat, A.; Michel, E.; Schoon, N.; Amelynck, C.; Labonnette, D.; Poulet, G.

2007-06-01

277

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

278

Resonance Ionization spectroscopy  

NASA Astrophysics Data System (ADS)

The paper presents a retrospective view on the appearance and early development of Resonance Ionization Spectroscopy (RIS) and briefly reviews its basic principles and unique characteristics. Most of the paper concentrates on RIS applications that are most active at present time including on-line facilities with particle accelerators, counting noble gas atoms, ultrasensitive and highly selective techniques, analytical systems which use RIS in combination with thermal atomization (TARIS), laser atomization (LARIS), ion sputtering (SIRIS) and collisional ionization (LEI).

Bekov, G. I.

1995-04-01

279

Resonance Ionization spectroscopy  

SciTech Connect

The paper presents a retrospective view on the appearance and early development of Resonance Ionization Spectroscopy (RIS) and briefly reviews its basic principles and unique characteristics. Most of the paper concentrates on RIS applications that are most active at present time including on-line facilities with particle accelerators, counting noble gas atoms, ultrasensitive and highly selective techniques, analytical systems which use RIS in combination with thermal atomization (TARIS), laser atomization (LARIS), ion sputtering (SIRIS) and collisional ionization (LEI)

Bekov, G. I. [Atom Sciences, Inc., 114 Ridgeway Center, Oak Ridge, TN, 37830 (United States); Institute of Spectroscopy Russian Academy of Sciences, Troitsk, Moscow Region 142092 (Russian Federation)

1995-04-01

280

Dynamic Hydrogen Ionization  

E-print Network

We investigate the ionization of hydrogen in a dynamic Solar atmosphere. We show that the time scale for ionization/recombination can be estimated from the eigenvalues of a modified rate matrix where the optically thick Lyman transitions that are in detailed balance have been excluded. We find that the time scale for ionization/recombination is dominated by the slow collisional leakage from the ground state to the first excited state. Throughout the chromosphere the time scale is long ($10^3$-$10^5$ s), except in shocks where the increased temperature and density shorten the time scale for ionization/recombination, especially in the upper chromosphere. Because the relaxation time scale is much longer than dynamic time scales, hydrogen ionization does not have time to reach its equilibrium value and its fluctuations are much smaller than the variation of its statistical equilibrium value appropriate for the instantaneous conditions. The ionization state tends to represent the higher temperature of the shocks, and the mean electron density is up to a factor of six higher than the electron density calculated in statistical equilibrium from the mean atmosphere. The simulations show that a static picture and a dynamic picture of the chromosphere are fundamentally different and that time variations are crucial for our understanding of the chromosphere itself and the spectral features formed there.

Mats Carlsson; Robert F. Stein

2002-02-16

281

Ionization Ability of Manganese Nanoparticles  

NASA Astrophysics Data System (ADS)

Manganese oxide nanoparticles (Mn-O NPs) were prepared through our novel method as reagents for laser desorption/ionization mass spectrometry (LDI-MS). Through the control of the reaction time in the chemical preparation method (0.5, 1, and 5 h), we succeeded in preparing three different types of manganese oxide particles. The particles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and DC magnetization measurements. These characterization results indicated that the manganese ions oxidized in aqueous alkaline solution, and that the spinel structure was retained for the Mn3O4 phase, which then gradually changed into the MnO2 phase. The mass spectra of substance P (MW = 1347.6) were measured by MALDI-TOF mass spectrometry with Mn-O NPs. The Mn-O NPs that reacted with 3-aminopropyltriethoxysilane(?-APTES) for 1 h or 5 h had higher ionization abilities than those reacted for 0.5 h. These different abilities are attributed to the different crystal structures of the prepared manganese oxides.

Hiroki, Tomoyuki; Shigeoka, Daiki; Kimura, Shinji; Mashino, Toshiyuki; Taira, Shu; Ichiyanagi, Yuko

2011-05-01

282

Positron ionization mass spectrometry: An organic mass spectrometrist's view  

SciTech Connect

We are currently engaged in a research program to study the ionization of polyatomic molecules by positrons. We refer to the technique herein as positron ionization mass spectrometry which includes all of the possible ionization mechanisms. In the course of this work we will attempt to characterize each of the important ionization mechanisms. Our ultimate objective is to explore the use of positron ionization mass spectrometry for chemical analysis. Several other groups have also begun to pursue aspects of positron ionization in parallel with our efforts although with somewhat different approaches and, perhaps with slightly different emphases. Recently, for example, Passner et al. have acquired mass spectra in a Penning trap resulting from the ionization of several different polyatomic molecules by near thermal kinetics energy positrons. Our research involves studying the different types of ionizing interactions of positrons with organic molecules, as a function of positron kinetic energy. For ionization of polyatomic molecules by positrons, several possible mechanisms are apparent from lifetime and scattering cross-section data. These mechanisms are discussed.

Glish, G.L.; Donohue, D.L.; McLuckey, S.A.; Eckenrode, B.A.; Hulett, L.D. Jr.

1990-01-01

283

Instantaneous ionization rate of H$_2^+$ in intense laser field; Interpretation of the Enhanced Ionization  

E-print Network

The fixed-nuclei full dimensional time-dependent Schr \\"odinger equation is directly solved for H$_2^+$ in the linearly polarized laser field of $I \\sim 1.0 \\times 10^{14}$W cm$^{-2}$ and $\\lambda \\sim 1064 $nm. Instantaneous ionization rate has been introduced and calculated by evaluating the instantaneous imaginary energy of the system. It is shown that positive (negative) values of instantaneous imaginary energy of the system represent the incoming (outgoing) instantaneous current of electron. This approach allows us to determine not only the instantaneous intensity but also the instantaneous direction of the electronic current. The instantaneous behavior of the electron wavepacket in intense laser field can thus be probed precisely. Details of the enhanced ionization rates are studied based on the instantaneous ionization rates. This approach gives direct evidence for existence of the effect of charge-resonance-enhanced multiphoton resonances of the quasienergy states (QES) with excited electronic states ...

Vafaee, M; Vafaee, Z; Katanforoush, A; Vafaee, Mohsen; Sabzyan, Hassan; Vafaee, Zahra; Katanforoush, Ali

2005-01-01

284

Negative Ion Sources: Magnetron and Penning  

E-print Network

The history of the magnetron and Penning electrode geometry is briefly outlined. Plasma generation by electrical discharge-driven electron impact ionization is described and the basic physics of plasma and electrodes relevant to magnetron and Penning discharges are explained. Negative ions and their applications are introduced, along with their production mechanisms. Caesium and surface production of negative ions are detailed. Technical details of how to build magnetron and Penning surface plasma sources are given, along with examples of specific sources from around the world. Failure modes are listed and lifetimes compared.

Faircloth, D C

2013-01-01

285

Prototype negative ion sources for RIB generation  

SciTech Connect

Radioactive ion beams (RIBs) of {sup 17}F and {sup 18}F are of interest for investigation of astrophysical phenomena such as the hot CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F{sup {minus}}, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. The authors have conceived and evaluated two prototype negative ion sources for potential use for RIB generation: (1) a direct extraction source and (2) a kinetic ejection source. Both sources utilize Cs vapor to enhance F{sup {minus}} formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F{sup {minus}} and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency {eta} for formation and extraction of F{sup {minus}} for the direct extraction negative ion source is found to be {eta} {approximately} 1.0% while the characteristic delay time {tau} for transport of F and fluorides through the source is typically, {eta} {approximately} 120s; the analogous efficiencies and delay times for the kinetic ejection negative ion source are, respectively: {eta} = {approximately}3.2% and {tau} = {approximately}70s.

Alton, G.D.; Murray, S.N. [Oak Ridge National Lab., TN (United States); Welton, R.F.; Williams, C. [Oak Ridge National Lab., TN (United States); [Oak Ridge Inst. of Science and Engineering, TN (United States); Cui, B. [China Inst. of Atomic Energy, Beijing (China)

1997-12-01

286

Resonance Ionization spectroscopy  

SciTech Connect

The paper presents a retrospective view on the appearance and early development of Resonance Ionization Spectroscopy (RIS) and briefly reviews its basic principles and unique characteristics. Most of the paper concentrates on RIS applications that are most active at present time including on-line facilities with particle accelerators, counting noble gas atoms, ultrasensitive and highly selective techniques, analytical systems which use RIS in combination with thermal atomization (TARIS), laser atomization (LARIS), ion sputtering (SIRIS) and collisional ionization (LEI). {copyright} 1995 {ital American} {ital Institute} {ital of} {ital Physics}

Bekov, G.I. [Atom Sciences, Inc., 114 Ridgeway Center, Oak Ridge, Tennessee, 37830 (United States)]|[Institute of Spectroscopy Russian Academy of Sciences, Troitsk, Moscow Region 142092 (Russian Federation)

1995-04-01

287

Negative thermal ion mass spectrometry of osmium, rhenium, and iridium  

Microsoft Academic Search

The authors report on a technique for obtaining intense ion beams of negatively charged oxides of Os, Re, and Ir by thermal ionization, in a conventional surface ionization mass spectrometer. It was found that the principal ion species of Os, Re, and Ir produced are OsOâ⁻, ReOâ⁻, and IrOâ⁻. The sharp distinction in the masses of the dominant molecular species

R. A. Creaser; D. A. Papanastassiou; G. J. Wasserburg

1991-01-01

288

Effects of impurities on wake chemical kinetics and electron density  

NASA Astrophysics Data System (ADS)

The present paper studies the effects of impurities on wake chemical kinetics and wake ionization. Such effects are examined through computation of wake flows composed of H2O, F2, CaF4, and Na-containing species added to the air constituents. A 26-species, 36-reaction chemical system is considered. An exact finite difference method for solving the axisymmetric boundary layer equations for chemical nonequilibrium wake flow is employed for both laminar and turbulent flows regions. In order to ascertain a variety of effects separately. nine different chemical subsystems of increasing complexity are treated. These are pure air, air-Na, air-F2, air-C2F4, air-F2-C2F4, air-H2O-Na, air-F2-Na, air-C2F4-Na, and air-C2F4-F2-Na. Calculated results demonstrate that impurities exert significant influences on wake ionization. Sodium can enhance electron concentration of pure air by 1-3 orders of magnitude and the electron decay mechanism of the air-C2F4 chemical subsystem results in production of negative F ions and removes most of the electrons.

Zhou, Xuehua

1992-09-01

289

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

290

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

291

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

292

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

293

Venturi easy ambient sonic-spray ionization.  

PubMed

The development and illustrative applications of an ambient ionization technique termed Venturi easy ambient sonic-spray ionization (V-EASI) is described. Its dual mode of operation with Venturi self-pumping makes V-EASI applicable to the direct mass spectrometric analysis of both liquid (V(L)-EASI) and solid (V(S)-EASI) samples. V-EASI is simple and easy to assemble, operating solely via the assistance of a sonic stream of nitrogen or air. The sonic gas stream causes two beneficial and integrated effects: (a) the self-pumping of solutions via the Venturi effect and (b) sonic-spray ionization (SSI) of analytes either in solution or resting on solid surfaces. In its liquid mode, V(L)-EASI is applicable to analytes in solution, forming negatively and/or positively charged intact molecular species in a soft fashion with little or no fragmentation. In its solid mode, V(S)-EASI relies on Venturi self-pumping of a proper SSI solvent solution in combination with SSI to form a stream of bipolar charged droplets that bombard the sample surface, causing desorption and ionization of the analyte molecules. As for its precursor technique (EASI), V-EASI generates bipolar droplets with considerably lower average charging, which increases selectivity for ionization with high signal-to-noise ratios and clean spectra dominated by single molecular species with minimal solvent ions. V-EASI also operates in a voltage-, heat-, and radiation-free fashion and is therefore free of thermal, electrical, or discharge interferences. PMID:21235233

Santos, Vanessa G; Regiani, Thaís; Dias, Fernanda F G; Romão, Wanderson; Jara, Jose Luis Paz; Klitzke, Clécio F; Coelho, Fernando; Eberlin, Marcos N

2011-02-15

294

Ionization state of the catalytic dyad Asp25/25' in the HIV-1 protease: NMR studies of site-specifically 13C labelled HIV-1 protease prepared by total chemical synthesis.  

PubMed

Total chemical synthesis was used to site-specifically (13)C-label active site Asp25 and Asp25' residues in HIV-1 protease and in several chemically synthesized analogues of the enzyme molecule. (13)C NMR measurements were consistent with a monoprotonated state for the catalytic dyad formed by the interacting Asp25, Asp25' side chain carboxyls. PMID:22659831

Torbeev, Vladimir Yu; Kent, Stephen B H

2012-08-14

295

Application of gas chromatography–surface ionization organic mass spectrometry to forensic toxicology  

Microsoft Academic Search

Surface ionization (SI), which consists in the formation of positive and negative ions along the course of thermal desorption of particles from a solid surface, was first applied as a detector for gas chromatography (GC), GC-surface ionization detection (SID); we developed many new sensitive methods for the determination of abused and other drugs by GC-SID. Recently, Fujii has devised a

Akira Ishii; Kanako Watanabe-Suzuki; Hiroshi Seno; Osamu Suzuki; Yoshinao Katsumata

2002-01-01

296

Method of forming a chemical composition  

DOEpatents

A method of forming a chemical composition such as a chemical hydride is described and which includes the steps of selecting a composition having chemical bonds and which is capable of forming a chemical hydride; providing a source of hydrogen; and exposing the selected composition to an amount of ionizing radiation to encourage the changing of the chemical bonds of the selected composition, and chemically reacting the selected composition with the source of hydrogen to facilitate the formation of a chemical hydride.

Bingham, Dennis N. (Idaho Falls, ID); Wilding, Bruce M. (Idaho Falls, ID); Klingler, Kerry M. (Idaho Falls, ID); Zollinger, William T. (Idaho Falls, ID); Wendt, Kraig M. (Idaho Falls, ID)

2007-10-09

297

Negative ion generator  

DOEpatents

A negative ion generator is formed from a magnetically insulated transmission line having a coating of graphite on the cathode for producing negative ions and a plurality of apertures on the opposed anode for the release of negative ions. Magnetic insulation keeps electrons from flowing from the cathode to the anode. A transverse magnetic field removes electrons which do escape through the apertures from the trajectory of the negative ions. 8 figs.

Stinnett, R.W.

1984-05-08

298

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

299

Removal of organic pollutants by surfactant modified zeolite: comparison between ionizable phenolic compounds and non-ionizable organic compounds.  

PubMed

The aim of this study was to examine the adsorption capability and mechanism of hexadecyltrimethylammonium modified zeolite, which was synthesized from coal fly ash, for the removal of ionizable phenolic compounds (phenol, p-chlorophenol and bisphenol A, with different pK(a)) and non-ionizable organic compounds (aniline, nitrobenzene, and naphthalene, with different hydrophobicity). The obtained zeolite was identified as type Na-P1 (Na(6)Al(6)Si(10)O(32)·12H(2)O, JCPDS code 39-0219), which is classified into the gismondine group with a pore size of 3.1 Å × 4.5 Å [100] and 2.8 Å × 4.8 Å [101]. The adsorption of the two kinds of organic compounds was due to loaded surfactant bilayer because modified zeolite showed great ability for the removal of organic chemicals while little adsorption by zeolite was observed. The isotherm data of ionizable compounds fitted well to the Langmuir model but those of non-ionizable chemicals followed a linear equation. Uptake of ionizable compounds depended greatly on pH, increasing at alkaline pH conditions. In contrary, adsorption of non-ionizable chemicals was essentially the same at all pH levels studied. The adsorption of both kinds of organic compounds correlated well to k(ow) value, suggesting that more hydrophobic organic contaminants are more easily retained by modified zeolite. Based on the different adsorption behavior, the uptake of non-ionizable pollutants was thought to be a single partitioning process into the surfactant bilayer. For ionizable compounds, however, interaction of the phenol group(s) with the positively charged "head" of surfactant additionally functions. PMID:22771348

Xie, Jie; Meng, Wenna; Wu, Deyi; Zhang, Zhenjia; Kong, Hainan

2012-09-15

300

A theoretical study of the gas-phase chemi-ionization reaction between uranium and oxygen atoms  

Microsoft Academic Search

The U+O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO+. Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U+O-->UO++e- is proposed. The U+O and Sm+O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions

Jozef Paulovic; Laura Gagliardi; John M. Dyke; Kimihiko Hirao

2005-01-01

301

An adaptive grid refinement strategy for the simulation of negative streamers  

E-print Network

: Adaptive grid refinements; Finite volumes; Elliptic-parabolic system; Negative streamers; Pulled front 0021­835 www.elsevier.com/locate/jcp #12;1. Introduction When non-ionized or lowly ionized matter is exposed the path of sparks and lightning [1] and they are believed to be directly observable as the multiple

Ebert, Ute

302

CNT-Based MEMS\\/NEMS Gas Ionizers for Portable Mass Spectrometry Applications  

Microsoft Academic Search

We report the fabrication and experimental characterization of a carbon nanotube (CNT)-based MEMS\\/NEMS electron impact gas ionizer with an integrated extractor gate for portable mass spectrometry. The ionizer achieves low-voltage ionization using sparse forests of plasma-enhanced chemical-vapor-deposited CNTs as field emitters and a proximal extractor grid with apertures aligned to the CNT forests to facilitate electron transmission. The extractor gate

Luis Fernando Velasquez-Garcia; Blaise Laurent Patrick Gassend; Akintunde Ibitayo Akinwande

2010-01-01

303

Direct analysis of large living organism by megavolt electrostatic ionization mass spectrometry.  

PubMed

A new ambient ionization method allowing the direct chemical analysis of living human body by mass spectrometry (MS) was developed. This MS method, namely Megavolt Electrostatic Ionization Mass Spectrometry, is based on electrostatic charging of a living individual to megavolt (MV) potential, illicit drugs, and explosives on skin/glove, flammable solvent on cloth/tissue paper, and volatile food substances in breath were readily ionized and detected by a mass spectrometer. PMID:24924518

Ng, Kwan-Ming; Tang, Ho-Wai; Man, Sin-Heng; Mak, Pui-Yuk; Choi, Yi-Ching; Wong, Melody Yee-Man

2014-09-01

304

Direct Analysis of Large Living Organism by Megavolt Electrostatic Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

A new ambient ionization method allowing the direct chemical analysis of living human body by mass spectrometry (MS) was developed. This MS method, namely Megavolt Electrostatic Ionization Mass Spectrometry, is based on electrostatic charging of a living individual to megavolt (MV) potential, illicit drugs, and explosives on skin/glove, flammable solvent on cloth/tissue paper, and volatile food substances in breath were readily ionized and detected by a mass spectrometer.

Ng, Kwan-Ming; Tang, Ho-Wai; Man, Sin-Heng; Mak, Pui-Yuk; Choi, Yi-Ching; Wong, Melody Yee-Man

2014-09-01

305

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

306

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

307

Effect of nickel grid parameters on production of negative hydrogen ions  

NASA Astrophysics Data System (ADS)

Negative hydrogen ions are produced by plasma-assisted catalytic ionization using a nickel grid. When positive ions passing through the grid are decelerated by an electric field, the extraction current density of passing positive ions is sharply reduced by neutralization and negative ionization of the ions. This phenomenon is found to depend on the specific surface area of the grid and the current density.

Oohara, W.; Yokoyama, H.; Takeda, Toshiaki; Maetani, Y.; Takeda, Takashi; Kawata, K.

2014-06-01

308

Plasma production via field ionization  

NASA Astrophysics Data System (ADS)

Plasma production via field ionization occurs when an incoming particle beam is sufficiently dense that the electric field associated with the beam ionizes a neutral vapor or gas. Experiments conducted at the Stanford Linear Accelerator Center explore the threshold conditions necessary to induce field ionization by an electron beam in a neutral lithium vapor. By independently varying the transverse beam size, number of electrons per bunch, or bunch length, the radial component of the electric field is controlled to be above or below the threshold for field ionization. Additional experiments ionized neutral xenon and neutral nitric oxide by varying the incoming beam’s bunch length. A self-ionized plasma is an essential step for the viability of plasma-based accelerators for future high-energy experiments.

O'Connell, C. L.; Barnes, C. D.; Decker, F.-J.; Hogan, M. J.; Iverson, R.; Krejcik, P.; Siemann, R.; Walz, D. R.; Clayton, C. E.; Huang, C.; Johnson, D. K.; Joshi, C.; Lu, W.; Marsh, K. A.; Mori, W.; Zhou, M.; Deng, S.; Katsouleas, T.; Muggli, P.; Oz, E.

2006-10-01

309

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

310

Electrostatic model of solid-state capacitor with ionizable charge traps  

NASA Astrophysics Data System (ADS)

We present the analysis of a simple electrostatic model of a solid-state capacitor with ionizable charge traps. It shows a charge–voltage characteristic resembling a chemical battery. With a given withstanding voltage and the same geometry, the energy density of the capacitor with ionizable traps will be lower than that of an ordinary capacitor with metal electrodes.

Shimada, Toshihiro; Nagahama, Taro; Yanase, Takashi

2014-08-01

311

Theory of field ionization  

NASA Astrophysics Data System (ADS)

We describe calculations of tunnelling rate constants for the field ion microscope (FIM) using various model potentials, and potentials obtained from self-consistent electronic structure calculations incorporating the full screening of an applied electric field. For our tunnelling calculations we have used the JWKB method of Haydock and Kingham. The expression for the tunnelling rate constant for a flat surface given by Haydock and Kingham is inaccurate and we have derived a new and reliable formula. We have also introduced a new tunnelling potential for the FIM which includes explicitly the effects of image potentials. None of the potentials for smooth surfaces give ionization zone widths which are narrow enough to account for experimental values. However, the width of the ionization zone is found to be a strongly decreasing function of the corrugation of the surface potential, and for large corrugations we can obtain results in plausible agreement with experimental values. For corrugated model surfaces we have found cross-surface variations in the tunnelling rate constant which may be sufficient to account for the atomic resolution of the FIM under normal operating conditions at liquid nitrogen temperatures.

Lam, S. C.; Needs, R. J.

1994-03-01

312

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

313

Transient ionization and solar flare X-ray spectra  

NASA Astrophysics Data System (ADS)

In this paper the effects of a transiently ionizing solar flare plasma on the X-ray spectrum of iron between 1.85 and 1.92 A are considered. The atomic physics of the nonequilibrium spectrum is discussed, and reasons for differences in appearance from ionization equilibrium spectra are explained. The effect of spectral resolution on the ability to detect transient ionization in the iron X-ray spectrum is illustrated by synthetic spectra. A synthetic transiently ionizing spectrum is applied to the interpretation of spectra obtained from the SOX 1 spectrometer on the Japanese Hinotori spacecraft. Some indications of transient ionization are found, although counting statistics negate a strong conclusion. A hypothetical spectrometer with about one order of magnitude more sensitivity than the SOX 1 Hinotori or the bent crystal spectrometer flown on the Solar Maximum Mission (SMM) is also considered. The ranges of plasma parameters such as plasma emission measure and density that are necessary for transient ionization to be detected by such an instrument are discussed.

Doschek, G. A.; Tanaka, K.

1987-12-01

314

Determination of organonitrogen pesticides in large volumes of surface water by liquid–liquid and solid-phase extraction using gas chromatography with nitrogen–phosphorus detection and liquid chromatography with atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

During a recent study to determine the fluxes and fates of contaminants in the St. Lawrence River, the majority of organonitrogen pesticides analysed in samples of surface water were found in the dissolved phase. This paper compares two extraction techniques and two analytical techniques for 10 chemicals (metolachlor, seven triazines and two degradation products of atrazine–cyanazine–propazine and simazine) in the

Hassan Sabik; Roger Jeannot

1998-01-01

315

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...

316

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

317

On Negative Mass  

NASA Astrophysics Data System (ADS)

The Schwarzschild solution to the matter free, spherically symmetric Einstein equations has one free parameter, the mass. But the mass can be of any sign. What is the meaning of the negative mass solutions? The answer to this question for the case of a pure Schwarzschild negative mass black solution is still elusive, however, in this essay, we will consider negative mass solutions within a Schwarzschild-de Sitter geometry. We show that there exist reasonable configurations of matter, bubbles of distributions of matter, that satisfy the dominant energy condition everywhere, that are nonsingular and well behaved everywhere, but correspond to the negative mass Schwarzschild-de Sitter geometry outside the matter distribution. These negative mass bubbles could occur as the end state of a quantum tunneling transition.

Belletête, Jonathan; Paranjape, M. B.

2013-06-01

318

[Ionizing and non-ionizing radiation (comparative risk estimations)].  

PubMed

The population has widely used mobile communication for already more than 15 years. It is important to note that the use of mobile communication has sharply changed the conditions of daily exposure of the population to EME We expose our brain daily for the first time in the entire civilization. The mobile phone is an open and uncontrollable source of electromagnetic radiation. The comparative risk estimation for the population of ionizing and non-ionizing radiation was carried out taking into account the real conditions of influence. Comparison of risks for the population of ionizing and non-ionizing radiation leads us to a conclusion that EMF RF exposure in conditions of wide use of mobile communication is potentially more harmful than ionizing radiation influence. PMID:22690585

Grigor'ev, Iu G

2012-01-01

319

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

320

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

321

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

322

Negative tandem mirror  

SciTech Connect

A tandem mirror configuration can be created by combining hot electron end cell plasmas with neutral beam pumping. A region of large negative potential formed in each end cell confines electrons in the central cell. The requirement of charge neutrality causes the central cell potential to become negative with respect to ground in order to confine ions as well as electrons. We discuss the method of producing and calculating the desired axial potential profile, and show the calculated axial potential profile and plasma parameters for a negative configuration of TMX-Upgrade.

Poulsen, P.; Allen, S.L.; Casper, T.A.; Grubb, D.P.; Jong, R.A.; Nexsen, W.E.; Porter, G.D.; Simonen, T.C.

1981-11-30

323

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

324

Theory of negative corona in oxygen  

NASA Astrophysics Data System (ADS)

Theoretical predictions are given of the development of the current and the distributions of charge and electric field in negative corona, or Trichel current pulses [G. W. Trichel, Phys. Rev. 54, 1078 (1938)], in oxygen at a pressure of 6.67 kPa (50 Torr). For a 10-mm-diam negative sphere located 20 mm from a positive plane, the calculated current pulse has a rise time of 11 ns, a pulse width of 50 ns, and a peak amplitude of 13 mA. These results agree satisfactorily with experimental values. The predicted velocity of the cathode-directed light pulse also agrees well with observations. The theory is based on the accurate numerical solution of Poisson's equation in conjunction with the continuity equations for electrons, positive ions, and negative ions. The effects of ionization, attachment, recombination, electron diffusion, and photoemission and ion secondary-electron emission from the cathode are all included. The initial steep rise of the current pulse is largely due to rapid ionization and electron motion in the high Laplacian field near the cathode. As the discharge develops, a dense plasma forms near the cathode, leading to strong space-charge distortion of the field. A prominent cathode fall region is formed immediately adjacent to the cathode, an almost zero field is formed within the plasma and the field is enhanced over the region to the anode. The current pulse is quenched because the low electric field in the plasma immobilizes the majority of the electrons which then undergo three-body attachment; furthermore, the cathode fall region becomes reduced to such a short distance that insignificant current is produced from this region. Because of the low mobility of the negative ions, the current remains low and the structure of the space-charge fields changes only slowly with time between pulses.

Morrow, R.

1985-09-01

325

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

326

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

327

Aliphatic Hydrocarbon Spectra by Helium Ionization Mass Spectrometry (HIMS) on a Modified Atmospheric-Pressure Source Designed for Electrospray Ionization  

NASA Astrophysics Data System (ADS)

Chemical-ionization techniques that use metastable species to ionize analytes traditionally use a flat pin or a sharp solid needle onto which the high potential needed to generate the discharge plasma is applied. We report here that direct analysis of samples containing volatile and semivolatile compounds, including saturated and unsaturated aliphatic hydrocarbons, can be achieved on any electrospray-ionization mass spectrometer by passing helium though the sample delivery metal capillary held at a high potential. In the helium plasma ionization source (HPIS) described here, the typical helium flow required (about 20-30 mL/min), was significantly lower than that needed for other helium-ionization sources. By this procedure, positive ions were generated by nominal hydride ion removal from molecules emanating from heated saturated hydrocarbons as large as tetratetracontane (C44H90), at capillary voltages ranging from 2.0 to 4.0 kV. Unsaturated hydrocarbons, on the other hand, underwent facile protonation under much lower capillary voltages (0.9 to 2.0 kV). Although saturated and monounsaturated hydrocarbons bearing the same number of carbon atoms generate ions of the same m/z ratio, a gas-phase deuterium exchange method is described to ascertain the identity of these isomeric ions originating from either protonation or hydride abstraction mechanisms. Moreover, mass spectrometric results obtained by exposing unsaturated hydrocarbons to D2O vapor in an HPIS-MS instrument confirmed that the proton donor for ionization of unsaturated hydrocarbons is protonated water.

Yang, Zhihua; Attygalle, Athula B.

2011-08-01

328

Atomic capture of negative muons and hadrons in Helium  

NASA Astrophysics Data System (ADS)

Collisions of slow negative heavy particles M with He atoms are considered using the semiclassical approximation for quantum coupling equations taking into account the two-particle channel M + He and the ionization channels M + He(+) + e. The ionization and atomic-capture cross sections are calculated. The kinetic characteristics of slowing-down and atomic capture of the particles in helium are obtained. The results for stopping power and slowing-down time of muons in helium are compared with the experimental data.

Dolinov, V. K.; Korenman, G. Ya.; Moskalenko, I. V.; Popov, V. P.

329

Modified calutron negative ion source operation and future plans  

SciTech Connect

Negative ion generation has advanced rapidly by employing the concept of surface ionization. The modified calutron has proven to be a successful tool to explore these concepts and provide solutions to the many problems which must be evaluated. Many features of the SITEX (Surface Ionization with Transverse Extraction) ion source are ideally suited to this exploration. Some of these features are; a ribbon-like plasma, electron control by transverse magnetic fields and the ability to separate the Cs oven parameters from those which control the positive ion generation.

Dagenhart, W.K.; Stirling, W.L.; Haselton, H.H.; Kelley, G.G.; Kim, J.; Tsai, C.C.; Whealton, J.H.

1980-01-01

330

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

331

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

332

Pulsed helium ionization detection system  

DOEpatents

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Ramsey, Roswitha S. (Knoxville, TN); Todd, Richard A. (Knoxville, TN)

1987-01-01

333

Pulsed helium ionization detection system  

DOEpatents

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Ramsey, R.S.; Todd, R.A.

1985-04-09

334

Optical ionization detector  

DOEpatents

An optical ionization detector wherein a beam of light is split so that one arm passes through a fiber optics and the other arm passes through a gas-filled region, and uses interferometry to detect density changes in a gas when charged particles pass through it. The gas-filled region of the detector is subjected to a high electric field and as a charged particle traverses this gas region electrons are freed from the cathode and accelerated so as to generate an electron avalanche which is collected on the anode. The gas density is effected by the electron avalanche formation and if the index or refraction is proportional to the gas density the index will change accordingly. The detector uses this index change by modulating the one arm of the split light beam passing through the gas, with respect to the other arm that is passed through the fiber optic. Upon recombining of the beams, interference fringe changes as a function of the index change indicates the passage of charged particles through the gaseous medium.

Wuest, Craig R. (Danville, CA); Lowry, Mark E. (Castro Valley, CA)

1994-01-01

335

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

336

Logical Construction of the Ionization Energy Theory and the Origin of Physical Categories  

E-print Network

Logical proofs and definitions are developed to establish (i) the energy-level spacings, \\xi for each chemical element (from the periodic table of chemical elements) can be converted to the ionization energies, (ii) both \\xi and the ionization energies are unique, and (iii) the averaged ionization energies of any quantum matter is proportional to the averaged ionization energies of its constituent chemical elements, if and only if \\xi not = 0 and \\xi is not an irrelevant constant. Physical sets are then constructed such that they are members of a specific physical class where each class belongs to a specific physical category, P. However, there is not a single structure-preserving functor from one energy-level spacing physical category, P(\\xi) to another P'(\\xi). Therefore, the existence of many P(\\xi) imply the existence of different categories of physical systems and quantum matter.

Andrew Das Arulsamy

2012-01-29

337

Ghosts as Negative Spinors  

E-print Network

We study the the properties of a BRST ghost degree of freedom complementary to a two-state spinor. We show that the ghost may be regarded as a unit carrier of negative entropy. We construct an irreducible representation of the su(2) Lie algebra with negative spin, equal to -1/2, on the ghost state space and discuss the representation of finite SU(2) group elements. The Casimir operator J^2 of the combined spinor-ghost system is nilpotent and coincides with the BRST operator Q. Using this, we discuss the sense in which the positive and negative spin representations cancel in the product to give an effectively trivial representation. We compute an effective dimension, equal to 1/2, and character for the ghost representation and argue that these are consistent with this cancellation.

Andre van Tonder

2002-07-11

338

Negative corona ‘tufts’  

NASA Astrophysics Data System (ADS)

Although the formation of bright spots (‘tufts’, ‘beads’) by negative wire corona is known, images of this phenomenon are not available in the literature. The images presented in this paper show that there are mechanisms that result in the formation of regular structures from negative corona ‘tufts’. Though ‘tufts’ of different intensity can co-exist, they ‘prefer’ neighbors of the same intensity. When the current density per unit of wire length is high, the ‘tufts’ ‘repel’ each other, and the brighter these ‘tufts’ are, the stronger this ‘repulsion’.

Gutsol, Alexander F.; Pyle, Walter R.

2014-10-01

339

Positive About Negative Numbers  

NSDL National Science Digital Library

This article is devoted to the mathematical topic of negative numbers and provides a series of primary resources designed to familiarize children with the notion of counting on either side of a central point. The article presents that the activities listed should be played sequentially to build precursory ideas in understanding negative numbers. All the games discussed in the article are linked on the page and have been cataloged separately: Incy Wincy Spider, Tug of War, Swimming Pool, Tug Harder, First Connect Three and lastly Sea Level.

Woodham, Liz

2011-01-01

340

Field ionization from carbon nanofibers  

E-print Network

The Micro Gas Analyzer project aims to develop power-efficient, high resolution, high sensitivity, portable and real-time gas sensors. We developed a field ionizer array based on gated CNTs. Arrays of CNTs are used because ...

Adeoti, Bosun J

2008-01-01

341

Plasma production via field ionization  

NASA Astrophysics Data System (ADS)

Plasma production via field ionization occurs when an incoming electron beam is sufficiently dense that the electric field associated with the beam ionizes the neutral vapor. Experiments at the Stanford Linear Accelerator Center (SLAC) explore the threshold conditions necessary to induce field ionization in a neutral lithium (Li) vapor. By independently varying the bunch length, transverse spot size or number of electrons per bunch, the radial component of the electric field is controlled to be above or below the threshold for field ionization. A self-ionized plasma is an essential step for the viability of plasma-based accelerators for future high-energy experiments. Based on the experimental results, the incoming beam ionizes the neutral Li vapor when its peak electric field is approximately 5 GV/m and higher. This electric field translates into a peak charge density of approximately 3 x 1016 cm-3. The experimental conditions are approximated and simulated in a 2-D particle-in-cell code, OOPIC. The code and the data correspond well in terms of the correct threshold conditions and the dependence on the critical beam parameters. In addition to the ionization threshold, the field ionization effects are characterized by the beam's energy loss through the Li vapor column due to the plasma wake field production. The peak and average energy loss as a result of wake production and beam propagation through the plasma is compared with simulation results from OOPIC. The simulation code accurately predicts the peak energy loss of the beam, but approximations in the code produce differences between the average energy loss measured and the loss calculated by the simulation.

O'Connell, Caolionn L.

342

Negative Plasma Densities Raise Questions  

SciTech Connect

Nearly all the matter encountered on Earth is either a solid, liquid, or gas. Yet plasma-the fourth state of matter-comprises more than 99 percent of the visible universe. Understanding the physical characteristics of plasmas is important to many areas of scientific research, such as the development of fusion as a clean, renewable energy source. Lawrence Livermore scientists study the physics of plasmas in their pursuit to create fusion energy, because plasmas are an integral part of that process. When deuterium and tritium are heated to the extreme temperatures needed to achieve and sustain a fusion reaction (about 100 million degrees), the electrons in these light atoms become separated from the nuclei. This process of separation is called ionization, and the resulting collection of negatively charged free electrons and positively charged nuclei is known as a plasma. Although plasmas and gases have many similar properties, plasmas differ from gases in that they are good conductors of electricity and can generate magnetic fields. For the past decade, x-ray laser interferometry has been used in the laboratory for measuring a plasma's index of refraction to determine plasma density. (The index of refraction for a given material is defined as the wavelength of light in a vacuum divided by the wavelength of light traveling through the material.) Until now, plasma physicists expected to find an index of refraction less than one. Researchers from Livermore and Colorado State University recently conducted experiments on aluminum plasmas at the Laboratory's COMET laser facility and observed results in which the index of refraction was greater than one. This surprising result implied a negative electron density. Livermore physicist Joseph Nilsen and his colleagues from Livermore and the University of Notre Dame have performed sophisticated calculations to explain this phenomenon. Previously, researchers believed that only free electrons contributed to the index of refraction. Nilsen and his colleagues posit that bound electrons attached to the ions in plasmas can greatly affect the index of refraction and make it greater than one. Furthermore, if the effect of bound electrons is ignored when analyzing experimental results from x-ray interferometry, the electron density of plasmas may be indeterminate or significantly under- or overestimated.

Hazi, A

2006-01-26

343

Electrospray ionization mass spectrometry fingerprinting of whisky: immediate proof of origin and authenticity.  

PubMed

Authentic samples of whisky produced in Scotland and USA and counterfeit whisky samples commercialized in Brazil have been directly submitted to electrospray ionization mass spectrometry (ESI-MS) analysis in both the negative and positive ion modes to assess the potential of this technique for simple and rapid quality control and proof of authenticity of whisky samples. ESI in the negative ion mode yields the most characteristic whisky fingerprinting mass spectra in just a few seconds by direct infusion of the samples, detecting the most polar or acidic components of each sample in their deprotonated anionic forms. No pre-treatment of the sample, such as extraction or derivatization or even dilution, is required. The analysis of the ESI(-)-MS data both by simple visual inspection but more particularly by chemometric data treatment enables separation of the whisky samples into three unequivocally distinct groups: Scotch, American and counterfeit whisky, whereas single malt and blended Scotch whiskies are also distinguished to some extent. As indicated by ESI-MS/MS analysis, the diagnostic anions are simple sugars, disaccharides and phenolic compounds. Direct infusion ESI-MS therefore provides immediate chemical fingerprinting of whisky samples for type, origin and quality control, as demonstrated herein for American, Scottish and counterfeit samples, whereas ESI-MS/MS analysis of diagnostic ions adds a second dimension of fingerprinting characterization when improved selectivity is desired. PMID:15912238

Møller, Jens K S; Catharino, Rodrigo R; Eberlin, Marcos N

2005-06-01

344

Negative ion formation in laser ion mobility increment spectrometer  

NASA Astrophysics Data System (ADS)

A new method is proposed and implemented, according to which small concentrations of organic compounds in the atmosphere are measured by combining the ion mobility increment spectrometer and laser ionization. The experimental setup makes use of the pulsed fourth-harmonic radiation of a YAG:Nd3+ laser (? = 266 nm). At high intensities ( q ˜ 107 W/cm2) of laser radiation, ion spectra with reactant peaks are observed, which are identical to the spectra obtained with traditional sources of ionization by corona discharge and ? radiation. The ion spectra obtained at low laser radiation intensities ( q ˜ 105 W/cm2) are free of background and reactant peaks, which ensures the high selectivity of the analysis. It is concluded that the mechanism of negative ion formation from the molecules of nitro compounds can change depending on the intensity of ionizing laser radiation.

Kotkovskii, G. E.; Tugaenko, A. V.; Chistyakov, A. A.

2010-03-01

345

Negative Transportation in French.  

ERIC Educational Resources Information Center

There is a class of verbs in French which require that their complement verb be in the indicative. However, if the matrix clause contains a negative or an interrogative, the complement verb is usually in the subjunctive, but sometimes in the indicative. Examples are the verbs "penser" and "croire" in sentences such as: 1) Elle ne croit pas que…

Prince, Ellen F.

346

Negative Mass Propulsion  

NASA Astrophysics Data System (ADS)

Schrödinger's analysis of the Dirac equation gives a hint for the existence of negative masses hidden behind positive masses. But their use for propulsion by reducing the inertia of matter for example, in the limit of macroscopic bodied with zero rest mass, depends on a technical solution to free them from their imprisonment by positive masses. It appears that there are basically two ways this might be achieved: 1. By the application of strong electromagnetic or gravitational fields or by high particle energies. 2. By searching for places in the universe where nature has already done this separation, and from where the negative masses can be mined. The first of these two possibilities is for all practical means excluded, because if possible at all, it would depend on electromagnetic or gravitational fields with strength beyond what is technically attainable, or on extremely large likewise not attainable particle energies. With regard to the 2nd possibility, it has been observed that non-baryonic cold dark matter tends to accumulate near the center of galaxies, or places in the universe which have a large gravitational potential well. Because of the equivalence principle of general relativity, the attraction towards the center of a gravitational potential well, produced by a positive mass, is for negative masses the same as for positive masses, and large amounts of negative masses might have over billions of years been trapped in these gravitational potential wells. Now it just happens that the center of the moon is a potential well, not too deep that it cannot be reached by making a tunnel through the moon, not possible for the deeper potential well of the earth, where the temperature and pressure are too high. Making a tunnel through the moon, provided there is a good supply of negative mass, could revolutionize interstellar space flight. A sequence of thermonuclear shape charges would make such tunnel technically feasible.

Winterberg, F.

347

Negative Electron Affinity Mechanism for Diamond Surfaces  

NASA Technical Reports Server (NTRS)

The energy distribution of the secondary electrons for chemical vacuum deposited diamond films with Negative Electron Affinity (NEA) was investigated. It was found that while for completely hydrogenated diamond surfaces the negative electron affinity peak in the energy spectrum of the secondary electrons is present for any energy of the primary electrons, for partially hydrogenated diamond surfaces there is a critical energy above which the peak is present in the spectrum. This critical energy increases sharply when hydrogen coverage of the diamond surface diminishes. This effect was explained by the change of the NEA from the true type for the completely hydrogenated surface to the effective type for the partially hydrogenated surfaces.

Krainsky, I. L.; Asnin, V. M.

1998-01-01

348

Quantifying Uranium Isotope Ratios Using Resonance Ionization Mass Spectrometry: The Influence of Laser Parameters on Relative Ionization Probability  

SciTech Connect

Resonance Ionization Mass Spectrometry (RIMS) has been developed as a method to measure relative uranium isotope abundances. In this approach, RIMS is used as an element-selective ionization process to provide a distinction between uranium atoms and potential isobars without the aid of chemical purification and separation. We explore the laser parameters critical to the ionization process and their effects on the measured isotope ratio. Specifically, the use of broad bandwidth lasers with automated feedback control of wavelength was applied to the measurement of {sup 235}U/{sup 238}U ratios to decrease laser-induced isotopic fractionation. By broadening the bandwidth of the first laser in a 3-color, 3-photon ionization process from a bandwidth of 1.8 GHz to about 10 GHz, the variation in sequential relative isotope abundance measurements decreased from >10% to less than 0.5%. This procedure was demonstrated for the direct interrogation of uranium oxide targets with essentially no sample preparation. A rate equation model for predicting the relative ionization probability has been developed to study the effect of variation in laser parameters on the measured isotope ratio. This work demonstrates that RIMS can be used for the robust measurement of uranium isotope ratios.

Isselhardt, B H

2011-09-06

349

Negative Emissions Technology  

NASA Astrophysics Data System (ADS)

Although `negative emissions' of carbon dioxide need not, in principle, involve use of biological processes to draw carbon out of the atmosphere, such `agricultural' sequestration' is the only known way to remove carbon from the atmosphere on time scales comparable to the time scale for anthropogenic increases in carbon emissions. In order to maintain the `negative emissions' the biomass must be used in such a way that the resulting carbon dioxide is separated and permanently sequestered. Two options for sequestration are in the topsoil and via geologic carbon sequestration. The former has multiple benefits, but the latter also is needed. Thus, although geologic carbon sequestration is viewed skeptically by some environmentalists as simply a way to keep using fossil fuels---it may be a key part of reversing accelerating climate forcing if rapid climate change is beginning to occur. I will first review the general approach of agricultural sequestration combined with use of resulting biofuels in a way that permits carbon separation and then geologic sequestration as a negative emissions technology. Then I discuss the process that is the focus of my company---the EPRIDA cycle. If deployed at a sufficiently large scale, it could reverse the increase in CO2 concentrations. I also estimate of benefits --carbon and other---of large scale deployment of negative emissions technologies. For example, using the EPRIDA cycle by planting and soil sequestering carbon in an area abut In 3X the size of Texas would remove the amount of carbon that is being accumulated worldwide each year. In addition to the atmospheric carbon removal, the EPRIDA approach also counters the depletion of carbon in the soil---increasing topsoil and its fertility; reduces the excess nitrogen in the water by eliminating the need for ammonium nitrate fertilizer and reduces fossil fuel reliance by providing biofuel and avoiding natural gas based fertilizer production.

Day, Danny

2006-04-01

350

Coagulase-negative staphylococci.  

PubMed

Coagulase-negative staphylococci, long considered to be harmless commensals or contaminants, have emerged as major pathogens as medical technology has advanced. They are a major cause of intravenous-catheter-associated bacteremia, endocarditis, otitis media, and infection of joint prostheses, vascular grafts, cardiac pacemakers, cerebrospinal fluid shunts, postoperative wounds, the urinary tract, and the eye. Therapy includes removal of infected foreign bodies and administration of appropriate antimicrobial agents. PMID:3282318

Neihart, R E; Fried, J S; Hodges, G R

1988-04-01

351

Characterizing Peptide Neutral Losses Induced by Negative Electron-Transfer Dissociation (NETD)  

NASA Astrophysics Data System (ADS)

We implemented negative electron-transfer dissociation (NETD) on a hybrid ion trap/Orbitrap mass spectrometer to conduct ion/ion reactions using peptide anions and radical reagent cations. In addition to sequence-informative ladders of a•- and x-type fragment ions, NETD generated intense neutral loss peaks corresponding to the entire or partial side-chain cleavage from amino acids constituting a given peptide. Thus, a critical step towards the characterization of this recently introduced fragmentation technique is a systematic study of synthetic peptides to identify common neutral losses and preferential fragmentation pathways. Examining 46 synthetic peptides with high mass accuracy and high resolution analysis permitted facile determination of the chemical composition of each neutral loss. We identified 19 unique neutral losses from 14 amino acids and three modified amino acids, and assessed the specificity and sensitivity of each neutral loss using a database of 1542 confidently identified peptides generated from NETD shotgun experiments employing high-pH separations and negative electrospray ionization. As residue-specific neutral losses indicate the presence of certain amino acids, we determined that many neutral losses have potential diagnostic utility. We envision this catalogue of neutral losses being incorporated into database search algorithms to improve peptide identification specificity and to further advance characterization of the acidic proteome.

Rumachik, Neil G.; McAlister, Graeme C.; Russell, Jason D.; Bailey, Derek J.; Wenger, Craig D.; Coon, Joshua J.

2012-04-01

352

Electron Capture in a Fully Ionized Plasma  

E-print Network

Properties of fully ionized water plasmas are discussed including plasma charge density oscillations and the screening of the Coulomb law especially in the dilute classical Debye regime. A kinetic model with two charged particle scattering events determines the transition rate per unit time for electron capture by a nucleus with the resulting nuclear transmutations. Two corrections to the recent Maiani et al. calculations are made: (i) The Debye screening length is only employed within its proper domain of validity. (ii) The WKB approximation employed by Maiani in the long De Broglie wave length limit is evidently invalid. We replace this incorrect approximation with mathematically rigorous Calogero inequalities in order to discuss the scattering wave functions. Having made these corrections, we find a verification for our previous results based on condensed matter electro-weak quantum field theory for nuclear transmutations in chemical batteries.

A. Widom; J. Swain; Y. N. Srivastava

2014-09-17

353

Protection against ionizing radiation with eicosanoids  

SciTech Connect

Prostaglandins (PGs) are extremely diverse in their pharmacological activities. They exhibit both antagonistic as well as cytoprotective properties in the pathogenesis of inflammation. Participation of PGs as chemical mediators in the regulation of immune responses and inflammation are increasingly apparent. The antagonistic properties of PGs have been implicated in a variety of symptoms resulting from exposure to ionizing radiation. Post-irradiation increases in small bowel motility, diarrhea, flatulence, abdominal pain, mucositis, and esophagitis have been attributed, in part, to excessive PG production. In contrast, exogenous PGs, particularly of the E type, have been shown to be cytoprotective against a variety of damaging agents, and a deficiency of endogeneous PG has been suggested to contribute to increase susceptibility to injury. These findings have provided much of the impetus to examine the potential cytoprotective effects of PGs in radiation injury.

Steel, L.K.; Catravas, G.N.

1988-01-01

354

Electron Capture in a Fully Ionized Plasma  

E-print Network

Properties of fully ionized water plasmas are discussed including plasma charge density oscillations and the screening of the Coulomb law especially in the dilute classical Debye regime. A kinetic model with two charged particle scattering events determines the transition rate per unit time for electron capture by a nucleus with the resulting nuclear transmutations. Two corrections to the recent Maiani et al. calculations are made: (i) The Debye screening length is only employed within its proper domain of validity. (ii) The WKB approximation employed by Maiani in the long De Broglie wave length limit is evidently invalid. We replace this incorrect approximation with mathematically rigorous Calogero inequalities in order to discuss the scattering wave functions. Having made these corrections, we find a verification for our previous results based on condensed matter electro-weak quantum field theory for nuclear transmutations in chemical batteries.

Widom, A; Srivastava, Y N

2014-01-01

355

Flow injection of liquid samples to a mass spectrometer with ionization under vacuum conditions: a combined ion source for single-photon and electron impact ionization.  

PubMed

Electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo-ionization (APPI) are the most important techniques for the ionization of liquid samples. However, working under atmospheric pressure conditions, all these techniques involve some chemical rather than purely physical processes, and therefore, side reactions often yield to matrix-dependent ionization efficiencies. Here, a system is presented that combines both soft single-photon ionization (SPI) and hard 70 eV electron impact ionization (EI) of dissolved compounds under vacuum conditions. A quadrupole mass spectrometer was modified to enable direct EI, a technique developed by Cappiello et al. to obtain library-searchable EI mass spectra as well as soft SPI mass spectra of sample solutions. An electron beam-pumped rare gas excimer lamp working at 126 nm was used as well as a focusable vacuum UV light source for single-photon ionization. Both techniques, EI and SPI, were applied successfully for flow injection experiments providing library-matchable EI fragment mass spectra and soft SPI mass spectra, showing dominant signals for the molecular ion. Four model compounds were analyzed: hexadecane, propofol, chlorpropham, and eugenol, with detection limits in the picomolar range. This novel combination of EI and SPI promises great analytical benefits, thanks to the possibility of combining database alignment for EI data and molecular mass information provided by SPI. Possible applications for the presented ionization technology system are a matrix-effect-free detection and a rapid screening of different complex mixtures without time-consuming sample preparation or separation techniques (e.g., for analysis of reaction solutions in combinatorial chemistry) or a switchable hard (EI) and soft (SPI) MS method as detection step for liquid chromatography. PMID:23812882

Schepler, Claudia; Sklorz, Martin; Passig, Johannes; Famiglini, Giorgio; Cappiello, Achille; Zimmermann, Ralf

2013-09-01

356

Mitochondrial perturbation negatively affects auxin signaling.  

PubMed

Mitochondria are crucial players in the signaling and metabolic homeostasis of the plant cell. The molecular components that orchestrate the underlying processes, however, are largely unknown. Using a chemical biology approach, we exploited the responsiveness of Arabidopsis UDP-glucosyltransferase-encoding UGT74E2 towards mitochondrial perturbation in order to look for novel mechanisms regulating mitochondria-to-nucleus communication. The most potent inducers of UGT74E2 shared a (2-furyl)acrylate (FAA) substructure that negatively affected mitochondrial function and was identified before as an auxin transcriptional inhibitor. Based on these premises, we demonstrated that perturbed mitochondria negatively affect the auxin signaling machinery. Moreover, chemical perturbation of polar auxin transport and auxin biosynthesis was sufficient to induce mitochondrial retrograde markers and their transcript abundance was constitutively elevated in the absence of the auxin transcriptional activators ARF7 and ARF19. PMID:24903751

Kerchev, Pavel Ivanov; De Clercq, Inge; Denecker, Jordi; Mühlenbock, Per; Kumpf, Robert; Nguyen, Long; Audenaert, Dominique; Dejonghe, Wim; Van Breusegem, Frank

2014-07-01

357

Effects of ionizing radiation in ginkgo and guarana [rapid communication  

NASA Astrophysics Data System (ADS)

Raw plant materials normally carry high bioburden due to their origin, offering potential hazards to consumers. The use of decontamination processes is therefore an important step towards the consumer safety and therapeutical efficiency. Several authors have reported the treatment of medicinal herbs with ionizing radiation. This work evaluated the effects of different radiation doses on the microbial burden and chemical constituents of ginkgo ( Ginkgo biloba L.) and guaraná ( Paullinia cupana H.B.K.).

Rabelo Soriani, Renata; Cristina Satomi, Lucilia; Pinto, Terezinha de Jesus A.

2005-07-01

358

Negative oxygen vacancies in HfO$_2$ as charge traps in high-k stacks  

Microsoft Academic Search

We calculated the optical excitation and thermal ionization energies of\\u000aoxygen vacancies in m-HfO$_2$ using atomic basis sets, a non-local density\\u000afunctional and periodic supercell. The thermal ionization energies of\\u000anegatively charged V$^-$ and V$^{2-}$ centres are consistent with values\\u000aobtained by the electrical measurements. The results suggest that negative\\u000aoxygen vacancies are the likely candidates for intrinsic electron traps

J. L. Gavartin; D. Munoz Ramo; A. L. Shluger; G. Bersuker; B. H. Lee

2006-01-01

359

Negative Chemotaxis inEscherichia coli  

Microsoft Academic Search

Negative chemotaxis, themovementoforga- nismsawayfromchemicals, wasdiscovered in bacteria along withpositive chemotaxis, move- menttowards chemicals, nearly acentury ago byEngelmann (19) andPfeffer (41). Theseand other workers ofthelate19thandearly 20th century reported taxis awayfromsalts, acids, bases, andalcohol, andfromoxygen athigh concentrations. Inrecent years, theonly studies ofnegative chemotaxis inbacteria havebeen thoseofLederberg (30)forphenol taxis in Salmonella typhimurium, Clayton (14) forsome aminoacids andsalts inRhodospirillum ru- brum, Baracchini andSherris (11)

WUNG-WAI TSO

1974-01-01

360

Universal screening method for the determination of US Environmental Protection Agency phenols at the lower ng l ?1 level in water samples by on-line solid-phase extraction–high-performance liquid chromatography–atmospheric pressure chemical ionization mass spectrometry within a single run  

Microsoft Academic Search

The applicability of a previously optimized method for the analysis of the US Environmental Protection Agency (EPA) regulations phenols, based on on-line solid-phase extraction coupled to liquid chromatography with mass spectrometric (MS) detection in different matrix loaded water samples is demonstrated. The comprehensive optimization of the mobile phase conditions and their influence on the ionization process in atmospheric pressure ionization

R. Wissiack; E. Rosenberg

2002-01-01

361

Polarized negative ions  

SciTech Connect

This paper presents a survey of methods, commonly in use or under development, to produce beams of polarized negative ions for injection into accelerators. A short summary recalls how the hyperfine interaction is used to obtain nuclear polarization in beams of atoms. Atomic-beam sources for light ions are discussed. If the best presently known techniques are incorporated in all stages of the source, polarized H/sup -/ and D/sup -/ beams in excess of 10 ..mu..A can probably be achieved. Production of polarized ions from fast (keV) beams of polarized atoms is treated separately for atoms in the H(25) excited state (Lamb-Shift source) and atoms in the H(1S) ground state. The negative ion beam from Lamb-Shift sources has reached a plateau just above 1 ..mu..A, but this beam current is adequate for many applications and the somewhat lower beam current is compensated by other desirable characteristics. Sources using fast polarized ground state atoms are in a stage of intense development. The next sections summarize production of polarized heavy ions by the atomic beam method, which is well established, and by optical pumping, which has recently been demonstrated to yield very large nuclear polarization. A short discussion of proposed ion sources for polarized /sup 3/He/sup -/ ions is followed by some concluding remarks.

Haeberli, W.

1981-04-01

362

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry  

Microsoft Academic Search

The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective\\u000a ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol\\u000a chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol\\u000a mass spectrometry (BAMS). EIP values were determined for

Scott C. Russell; Gregg Czerwieniec; Carlito Lebrilla; Herbert Tobias; David P. Fergenson; Paul Steele; Maurice Pitesky; Joanne Horn; Abneesh Srivastava; Matthias Frank; Eric E. Gard

2004-01-01

363

A theoretical study of the gas-phase chemi-ionization reaction between uranium and oxygen atoms  

NASA Astrophysics Data System (ADS)

The U +O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO +. Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U +O?UO++e- is proposed. The U +O and Sm +O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions to be studied theoretically in this way.

Paulovi?, Jozef; Gagliardi, Laura; Dyke, John M.; Hirao, Kimihiko

2005-04-01

364

A theoretical study of the gas-phase chemi-ionization reaction between uranium and oxygen atoms.  

PubMed

The U+O chemi-ionization reaction has been investigated by quantum chemical methods. Potential-energy curves have been calculated for several electronic states of UO and UO(+). Comparison with the available spectroscopic and thermodynamic values for these species is reported and a mechanism for the chemi-ionization reaction U+O-->UO(+)+e(-) is proposed. The U+O and Sm+O chemi-ionization reactions are the first two metal-plus-oxidant chemi-ionization reactions to be studied theoretically in this way. PMID:15847532

Paulovic, Jozef; Gagliardi, Laura; Dyke, John M; Hirao, Kimihiko

2005-04-01

365

Ionizing radiation and a wood-based biorefinery  

NASA Astrophysics Data System (ADS)

Woody biomass is widely available around the world. Cellulose is the major structural component of woody biomass and is the most abundant polymer synthesized by nature, with hemicellulose and lignin being second and third. Despite this great abundance, woody biomass has seen limited application outside of the paper and lumber industries. Its use as a feedstock for fuels and chemicals has been limited because of its highly crystalline structure, inaccessible morphology, and limited solubility (recalcitrance). Any economic use of woody biomass for the production of fuels and chemicals requires a "pretreatment" process to enhance the accessibility of the biomass to enzymes and/or chemical reagents. Electron beams (EB), X-rays, and gamma rays produce ions in a material which can then initiate chemical reactions and cleavage of chemical bonds. Such ionizing radiation predominantly scissions and degrades or depolymerizes both cellulose and hemicelluloses, less is known about its effects on lignin. This paper discusses how ionizing radiation can be used to make a wood-based biorefinery more environmentally friendly and profitable for its operators.

Driscoll, Mark S.; Stipanovic, Arthur J.; Cheng, Kun; Barber, Vincent A.; Manning, Mellony; Smith, Jennifer L.; Sundar, Smith

2014-01-01

366

Structural characterization of alpha,beta-unsaturated aldehydes by GC/MS is dependent upon ionization method.  

PubMed

alpha,beta-unsaturated aldehydes are toxic products of lipid peroxidation. Detection and characterization of these aldehydes is important in many human disease states as well as in the food industry. Our study shows that electron ionization-mass spectrometry (EI-MS) and positive-ion chemical ionization-mass spectrometry (PICI-MS), but not electron capture negative ionization-mass spectrometry (ECNI-MS), can be used to detect the C4-hydroxylation state of alpha,beta-unsaturated aldehydes derivatized with pentafluorobenzyl hydroxylamine alone. EI-MS and PICI-MS spectra of 4-hydroxy-2-alkenals contained a fragment with m/z 252, whereas spectra of 2-alkenals contained a fragment with m/z 250. These fragments are consistent with fragmentation between C3 and C4 with transfer of two hydrogens from C4 and the C4 hydroxyl group in the case of 4-hydroxy-2-alkenals. In addition, EI-MS and PICI-MS were able to distinguish 4-hydroxy-2-alkenals and 2-alkenals from 4-keto-2-alkenals and 4-hydroxyalkanals. On the other hand, ECNI-MS provided complex spectra regarding C4-hydroxylation state. Furthermore, the syn- and anti-configurations of PFB-oximes had different resultant spectra using ECNI-MS, but not with EI-MS or PICI-MS. These data indicate that EI-MS and PICI-MS are more amenable for structural analysis of alpha,beta-unsaturated aldehydes than ECNI-MS. PMID:18592287

Long, Eric K; Smoliakova, Irina; Honzatko, Ales; Picklo, Matthew J

2008-08-01

367

Chemical Exposure, ras Oncogene Activation, and  

E-print Network

- negative (ras-negative) patients were compared. Earlier studies (8-11) had shown a link between chemical in chemotherapy with aberrations in the -5/-5q and -7/-7q chromosomal regions; association of occupational

California at Berkeley, University of

368

Trends in resonance ionization spectroscopy  

SciTech Connect

The author reviews the history of resonance ionization spectroscopy and then comments on the delineations of RIS with reference to many related laser processes. The substance of the paper deals with the trends in RIS and especially how the needs for sensitive analytical methods have overshadowed the orginal plan to study excited species. 9 refs., 1 fig.

Hurst, G.S.

1986-01-01

369

CEILCOTE IONIZING WET SCRUBBER EVALUATION  

EPA Science Inventory

The report gives results of an evaluation of a Ceilcote ionizing wet scrubber installed on a refractory brick kiln. Tests involved particulate mass emission, particle size distribution, and opacity. Overall efficiency was 93% with an average outlet opacity determined with a heate...

370

Do `negative' temperatures exist?  

NASA Astrophysics Data System (ADS)

A modification of the second law is required for a system with a bounded density of states and not the introduction of a `negative' temperature scale. The ascending and descending branches of the entropy versus energy curve describe particle and hole states, having thermal equations of state that are given by the Fermi and logistic distributions, respectively. Conservation of energy requires isentropic states to be isothermal. The effect of adiabatically reversing the field is entirely mechanical because the only difference between the two states is their energies. The laws of large and small numbers, leading to the normal and Poisson approximations, characterize statistically the states of infinite and zero temperatures, respectively. Since the heat capacity also vanishes in the state of maximum disorder, the third law can be generalized in systems with a bounded density of states: the entropy tends to a constant as the temperature tends to either zero or infinity.

Lavenda, B. H.

1999-06-01

371

Negative Optical Torque  

NASA Astrophysics Data System (ADS)

Light carries angular momentum, and as such it can exert torques on material objects. Applications of these opto-mechanical effects were limited initially due to their smallness in magnitude, but later becomes powerful and versatile after the invention of laser. Novel and practical approaches for harvesting light for particle rotation have since been demonstrated, where the structure is always subjected to a positive optical torque along a certain axis if the incident angular momentum has a positive projection on the same axis. We report here an interesting phenomenon of ``negative optical torque'', meaning that incoming photons carrying angular momentum rotate an object in the opposite sense. Surprisingly this can be realized quite straightforwardly in simple planar structures. Field retardation is a necessary condition and discrete rotational symmetry of material object plays an important role. The optimal conditions are explored and explained.

Chen, Jun; Ng, Jack; Ding, Kun; Fung, Kin Hung; Lin, Zhifang; Chan, C. T.

2014-09-01

372

Primitive Virtual Negative Charge  

E-print Network

Physical fields, such as gravity and electromagnetic field, are interpreted as results from rearrangement of vacuum particles to get the equilibrium of net charge density and net mass density in 4-dimensional complex space. Then, both fields should interact to each other in that physical interaction is considered as a field-to-field interaction. Hence, Mass-Charge interaction is introduced with primitive-virtual negative charge defined for the mass. With the concept of Mass-Charge interaction electric equilibrium of the earth is discussed, especially about the electric field and magnetic field of the earth. For unsettled phenomena related with the earth's gravity, such as antigravity phenomenon, gravity anomalies during the solar eclipses, the connection between geomagnetic storms and earthquakes, etc., possible explanations are discussed.

Kiyoung Kim

2008-11-04

373

Primitive Virtual Negative Charge  

E-print Network

Physical fields, such as gravity and electromagnetic field, are interpreted as results from rearrangement of vacuum particles to get the equilibrium of net charge density and net mass density in 4-dimensional complex space. Then, both fields should interact to each other in that physical interaction is considered as a field-to-field interaction. Hence, Mass-Charge interaction is introduced with primitive-virtual negative charge defined for the mass. With the concept of Mass-Charge interaction electric equilibrium of the earth is discussed, especially about the electric field and magnetic field of the earth. For unsettled phenomena related with the earth's gravity, such as antigravity phenomenon, gravity anomalies during the solar eclipses, the connection between geomagnetic storms and earthquakes, etc., possible explanations are discussed.

Kim, Kiyoung

2008-01-01

374

Carbon nanotube-based field ionization vacuum  

E-print Network

We report the development of a novel micropump architecture that uses arrays of isolated vertical carbon nanotubes (CNT) to field ionize gas particles. The ionized gas molecules are accelerated to and implanted into a ...

Jang, Daniel, M. Eng. Massachusetts Institute of Technology

2012-01-01

375

Damage to DNA Resulting from Ionizing Radiation  

NASA Astrophysics Data System (ADS)

This work studies the mechanism by which radiation causes biological damage. In general, radiation leads to ionized molecules in solution, which can produce free radical molecules through a series of chemical reactions. These free radicals can chemically attack the DNA molecule resulting in breaks in the phosphate-sugar backbone of the molecule. The molecule may break into smaller pieces or recombine into different shapes. If the molecule were in a living cell, such damage would most likely lead to cell death. This work involves irradiating extra-cellular, non-living DNA plasmid in solution and assessing the amount of damage done to the plasmid. After irradiating the vials at various high doses ( 0.05-10 Gy), the resulting DNA fragments were analyzed via gel electrophoresis. We can therefore look at the fraction of the sample that is still intact compared to the smaller pieces that have resulted from radiation-induced strand breaks in the DNA. A better understanding of radiation and its ability to damage DNA (and kill cells) may lead to improved methods for radiation therapy. (This work was possible through the cooperation and assistance from the staff and facilities at Carolinas Hospital in Florence, SC.)

Jokisch, Derek W.; Shannon, Timothy E.; Will Quick, S.

2002-10-01

376

Development of capabilities for imaging mass spectrometry under ambient conditions with desorption electrospray ionization (DESI)  

NASA Astrophysics Data System (ADS)

Aspects of the development of mass spectrometry over the past three decades are briefly reviewed and growth points in the subject are identified. Molecular imaging by mass spectrometry is one such growth area. The development of a capability for 2D chemical imaging of surfaces is described, based on the combination of a desorption electrospray ionization (DESI) ion source with an automated surface stage capable of x, y translational motion. The lateral resolution of this new system is found to be less than 200 microns, using a test ink pattern. Chemical imaging of surfaces is demonstrated using model examples of organic and biological systems: (i) imaging of a 2D pattern written in different colored inks on photographic paper and (ii) imaging of thin coronal sections of rat brain tissue fixed onto a glass microscope slide. In both cases, full mass spectra are recorded as a function of x,y-position on the surface. In the chemical imaging example, the distributions of the two different inks on the paper surface were mapped by tracking the abundance of the intact organic cation which characterizes each particular ink dye. In the tissue imaging example, distributions of specific lipids in coronal sections of rat brain tissue were followed from the abundance distributions in 2D space of the deprotonated lipid molecules recorded in the negative ion mass spectra. These latter distributions reveal distinct anatomical features of the rat brain. The results of these studies demonstrate the feasibility of performing surface imaging studies using DESI and show that at this stage of its development it has a lateral spatial resolution of a few hundred microns.

Ifa, Demian R.; Wiseman, Justin M.; Song, Qingyu; Cooks, R. Graham

2007-01-01

377

Cesium Delivery System for Negative Ion Source at IPR  

NASA Astrophysics Data System (ADS)

The technique of surface production of negative ions using cesium, Cs, has been efficiently exploited over the years for producing negative ion beams with increased current densities from negative ion sources used on neutral beam lines. Deposition of Cs on the source walls and the plasma grid lowers the work function and therefore enables a higher yield of H-, when hydrogen particles (H and/or Hx+) strike these surfaces. A single driver RF based (100 kW, 1 MHz) negative ion source test bed, ROBIN, is being set up at IPR under a technical collaboration between IPR and IPP, Germany. The optimization of the Cs oven design to be used on this facility as well as multidriver sources is underway. The characterization experiments of such a Cs delivery system with a 1 g Cs inventory have been carried out using surface ionization technique. The experiments have been carried by delivering Cs into a vacuum chamber without plasma. The linear motion of the surface ionization detector, SID, attached with a linear motion feedthrough allows measuring the angular distribution of the Cs coming out of the oven. Based on the experimental results, a Cs oven for ROBIN has been proposed. The Cs oven design and experimental results of the prototype Cs oven are reported and discussed in the paper.

Bansal, G.; Pandya, K.; Bandyopadhyay, M.; Chakraborty, A.; Singh, M. J.; Soni, J.; Gahlaut, A.; Parmar, K. G.

2011-09-01

378

Ionization of the atmosphere caused by energetic particles  

NASA Astrophysics Data System (ADS)

Energetic particles from different sources are precipitating into the atmosphere, causing ionization and different chemical follow-ups. Focussing on low and mid-energies, this presentation will concentrate on the solar and magnetospheric particle spectrum, representing the particle forcing from the thermosphere down to the tropopause. While the precipitation of solar particles can be described in simple patterns, the magnetospheric precipitation is intensively modulated by the geomagnetic field, varying with latitude, longitude, geomagnetic disturbance, and MLT, ending up in a fluctuating auroral oval. Modeling the resulting ionization consequently is confronted with numerous challenges, ranging from sparse measurements (in-situ measuring satellites vs. global coverage), contaminated detectors, strong flux variation in space and time and finally the conversion of flux measurements into (3D) ionization profiles. This presentation will give an overview of the general setup, discuss main aspects in modeling particle precipitation and present some recent advances with the help of the Atmospheric Ionization Module OSnabrueck (AIMOS). AIMOS is based on a Geant4 Monte-Carlo Simulation for particle interactions with the atmosphere and in-situ particle measurements from the POES and GOES satellites.

Maik Wissing, Jan; Kallenrode, May-Britt

379

Terahertz spectroscopy of ionized air and explosive vapor  

NASA Astrophysics Data System (ADS)

In the past it has been demonstrated that terahertz spectroscopy could identify various chemical agents and explosives in solid and liquid phases. However peaks and dips in the terahertz spectra obtained from solid and liquid phases are not sharp and often ambiguous or ill-defined, as the interferences among the molecules in the solid or liquid obscure the molecule's characteristic resonances. Hence there has been considerable interest in obtaining terahertz spectrum of gas phase. Recently we have increased terahertz output power of our terahertz spectrometer, and measured terahertz spectra of gases, including water vapor, and ionized air produced by various ionization sources as well as explosive vapors. Our experiments revealed: (1) our terahertz spectrum of water vapor was highly consistent with other published data, (2) the spectra of ionized air produced by corona discharge and nuclear isotopes including Am-241, Bi-207, Ba-133, Co-60, Na-22 and Cs-137 were all different, and the characteristic spectrum changes largely depending on the type of ionization source, and (3) terahertz spectra of explosive vapor taken from TNT, PETN and RDX which were dissolved in acetonitrile or water exhibit very sharp resonance peaks and dips. We will present details of our experimental results.

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

2011-03-01

380

29 CFR 1926.53 - Ionizing radiation.  

Code of Federal Regulations, 2012 CFR

...2012-07-01 2012-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor...Environmental Controls § 1926.53 Ionizing radiation. (a) In construction and related...involving the use of sources of ionizing radiation, the pertinent provisions of the...

2012-07-01

381

29 CFR 1926.53 - Ionizing radiation.  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor...Environmental Controls § 1926.53 Ionizing radiation. (a) In construction and related...involving the use of sources of ionizing radiation, the pertinent provisions of the...

2011-07-01

382

29 CFR 1926.53 - Ionizing radiation.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor...Environmental Controls § 1926.53 Ionizing radiation. (a) In construction and related...involving the use of sources of ionizing radiation, the pertinent provisions of the...

2010-07-01

383

29 CFR 1926.53 - Ionizing radiation.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor...Environmental Controls § 1926.53 Ionizing radiation. (a) In construction and related...involving the use of sources of ionizing radiation, the pertinent provisions of the...

2013-07-01

384

29 CFR 1926.53 - Ionizing radiation.  

...2014-07-01 2014-07-01 false Ionizing radiation. 1926.53 Section 1926.53 Labor...Environmental Controls § 1926.53 Ionizing radiation. (a) In construction and related...involving the use of sources of ionizing radiation, the pertinent provisions of the...

2014-07-01

385

Negative Ions for Emerging Interdisciplinary Applications  

NASA Astrophysics Data System (ADS)

In many applications related to ion beam-materials interactions negative ions are particularly desirable due to its merit to yield a very low surface charge-up voltage, ˜ a few volts, for both electrically isolated surfaces and insulators. Some important applications pertaining to ion beam-material interactions include surface analysis by secondary ion mass spectrometry (SIMS), voltage-contrast microscopy for semiconductor device inspection, materials processing, and ion beam lithography. These applications primarily require vacuum environments. On the other hand, a distinct area of activities constitutes formation of ions and ion transport in ambient environmental conditions, i.e., at atmospheric pressures. In this context, ion mobility spectrometry (IMS) is an important analytical device that uses negative ions and operates at ambient conditions. IMS is widely used in both physical and biological sciences including monitoring environmental conditions, security screening and disease detection. This article highlights several critical issues related to the ionization sources and ion transport in IMS. Additionally, the critical issues related to ion sources, transport and focusing are discussed in the context of SIMS with sub-micrometer spatial resolution.

Guharay, Samar K.

2011-09-01

386

Desorption electrospray ionization mass spectrometry (DESI-MS) applied to the speciation of arsenic compounds from fern leaves.  

PubMed

The different chemical forms of arsenic compounds, including inorganic and organic species, present distinct environmental impacts and toxicities. Desorption electrospray ionization mass spectrometry (DESI-MS) is an excellent technique for in situ analysis, as it operates under atmospheric pressure and room temperature and is conducted with no/minimal sample pretreatment. Aimed at expanding its scope, DESI-MS is applied herein for the quick and reliable detection of inorganic (arsenate--As(V): AsO4(3-) and arsenite--As(III): AsO2(-)) and organic (dimethylarsinic acid--DMA: (CH3)2AsO(OH) and disodium methyl arsonate hexahydrate: CH3AsO3·2Na·6H2O) arsenic compounds in fern leaves. Operational conditions of DESI-MS were optimized with DMA standard deposited on paper surfaces to improve ionization efficiency and detection limits. Mass spectra data for all arsenic species were acquired in both the positive and negative ion modes. The positive ion mode was shown to be useful in detecting both the organic and inorganic arsenic compounds. The negative ion mode was shown only to be useful in detecting As(V) species. Moreover, MS/MS spectra were recorded to confirm the identity of each arsenic compound by the characteristic fragmentation profiles. Optimized conditions of DESI-MS were applied to the analysis of fern leaves. LC-ICP-MS was employed to confirm the results obtained by DESI-MS and to quantify the arsenic species in fern leaves. The results confirmed the applicability of DESI-MS in detecting arsenic compounds in complex matrices. PMID:23873446

de Abreu, Lívia Botelho; Augusti, Rodinei; Schmidt, Lucas; Dressler, Valderi Luiz; Flores, Erico Marlon de Moraes; Nascentes, Clésia Cristina

2013-09-01

387

Improved negative ion source  

DOEpatents

A method and apparatus for providing a negative ion source accelerates electrons away from a hot filament electron emitter into a region of crossed electric and magnetic fields arranged in a magnetron configuration. During a portion of the resulting cycloidal path, the electron velocity is reduced below its initial value. The electron accelerates as it leaves the surface at a rate of only slightly less than if there were no magnetic field, thereby preventing a charge buildup at the surface of the emitter. As the electron traverses the cycloid, it is decelerated during the second, third, and fourth quadrants, then reaccelerated as it approaches the end of the fourth quadrant to regain its original velocity. The minimum velocity occurs during the fourth quadrant, and corresponds to an electron temperature of 200 to 500/sup 0/C for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source using the above-described thermalized electrons is also disclosed.

Delmore, J.E.

1984-05-01

388

Negativity bias and basic values.  

PubMed

Basic values explain more variance in political attitudes and preferences than other personality and sociodemographic variables. The values most relevant to the political domain are those likely to reflect the degree of negativity bias. Value conflicts that represent negativity bias clarify differences between what worries conservatives and liberals and suggest that relations between ideology and negativity bias are linear. PMID:24970450

Schwartz, Shalom H

2014-06-01

389

Ionization model results of ionocraft  

E-print Network

An ionocraft is a small instrument that generates net vertical force from electrostatic field. A model of ionization and flow is built to explain this force. The assumption of a threshold field density and the constant charge density is applied to simplify the flow model. With these assumptions, corresponding simulation results and comparison with experimental data, we have shown that this model is sufficient to explain the force on the ionocraft.

Ma, Chen; Tang, Yuanhui; Lu, Rongde; Ye, Bangjiao

2014-01-01

390

Ionized oxygen around starforming galaxies .  

NASA Astrophysics Data System (ADS)

We consider the evolution of metal-enriched gas exposed to a superposition of time-dependent radiation field of a nearby starburt galaxy and nearly invariant (on timescales 100 Myr) extragalactic ionization background. We study the evolution of ionic species depending on the galactic mass and star formation rate, and derive conditions for the highly ionized oxygen, OVI, to appear in extended galactic haloes in absorption or emission spectra. We have found that the maximum OVI fraction can reach ˜ 0.4-0.6 under the action of both ionizing radiation field, which is typical in haloes of starforming galaxies, and the extragalactic background, the fraction remains high in a wide temperature range. We study the dependence of the OVI ion fraction on gas density and found that for the typical density of the circumgalactic gas, n˜ (0.5-2)× 10-4 cm-3 the OVI fraction is higher than ˜ 0.1 at distances r˜ 50-120 kpc. We have shown that the OVI fraction is high enough that even for ˜ 0.1 Z_? metallicity we can explain large OVI column densities (log [N(OVI), {cm-2]} ˜ 14.5 - 15.3) observed in the haloes of staforming galaxies by Tumlinson et al. (2011). Thus, the requirements to the sources of oxygen supply into the extended haloes become reasonably conservative.

Vasiliev, E. O.; Ryabova, M. V.; Shchekinov, Yu. A.

391

Electrospray ionization mass spectrometry of oligosaccharides derived from fucoidan of Ascophyllum nodosum  

Microsoft Academic Search

Algal fucoidan is a complex sulfated polysaccharide whose structural characterization requires powerful spectroscopic methodologies. While most of the structural investigations reported so far have been performed using NMR as the main spectroscopic method, we report herein data obtained by negative electrospray ionization mass spectrometry. MS analysis has been carried out on oligosaccharides obtained by partial hydrolysis of fucoidan from the

Régis Daniel; Lionel Chevolot; Montse Carrascal; Bérangère Tissot; Paulo A. S. Mourão; Joaquin Abian

2007-01-01

392

Chemical Mechanical Planarization- Chemical  

NSDL National Science Digital Library

This website includes an animation which illustrates the chemical action of slurry in the chemical-mechanical planarization process. Objective: Explain the mechanical and chemical steps in the CMP process. This simulation is from Module 068 of the Process & Equipment III Cluster of the MATEC Module Library (MML). Find this animation under the section "Process & Equipment III." To view other clusters or for more information about the MML visit http://matec.org/ps/library3/process_I.shtmlKey Phrase: MATEC Animation

2012-12-07

393

The effect of ionizing gamma radiation on natural and synthetic fibers and its implications for the forensic examination of fiber evidence.  

PubMed

Circumstances of criminal activities involving radioactive materials may mean fiber evidence recovered from a crime scene could have been exposed to materials emitting ionizing radiation. The consequences of radiation exposed fibers on the result of the forensic analysis and interpretation is explored. The effect of exposure to 1-1000 kGy radiation doses in natural and synthetic fibers was noticeable using comparative forensic examination methods, such as optical microscopy, microspectrophotometry, and thin-layer chromatography. Fourier transform infrared spectroscopy analysis showed no signs of radiation-induced chemical changes in any of the fiber structures. The outcome of the comparative methods highlights the risk of "false negatives" associated in comparing colors of recovered fibers that may have been exposed to unknown radiation doses. Consideration of such results supports the requirement to know the context, including the environmental conditions, as much as possible before undertaking a forensic fiber examination. PMID:21306372

Colella, Michael; Parkinson, Andrew; Evans, Tegan; Robertson, J; Roux, Claude

2011-05-01

394

Pulsed extraction of ionization from helium buffer gas  

E-print Network

The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a Particle-In-Cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.

D. J. Morrissey; G. Bollen; M. Facina; S. Schwarz

2008-08-13

395

Elemental diffusion and segregation processes in partially ionized solar plasma  

NASA Astrophysics Data System (ADS)

Although diffusion is usually associated with equalizing of the chemical composition, the pressure and temperature gradients inside the Sun cause elemental diffusion segregation. While light hydrogen is flowing up to the solar envelope, helium and heavier elements are settling down to the core. The target of our simulation is an accurate estimation of the settling rate in solar plasma during the course of solar evolution. The rate of helium depletion in the envelope is a key parameter of the solar evolution and depends on position and conditions around the base of the convective mixing zone. The rate of heavy element settling is sensitive to the degree of ionization and interaction with the radiation flux. We estimate the effect of ion ionization on the settling rate for several heavy elements up to iron in the framework of the LTE assumption and the thermodynamic calculation according to SAHA-S EOS.

Gorshkov, Alexey B.; Baturin, Vladimir A.

2010-07-01

396

NON-CHEMICAL IMPACTS (SYSTEMS ANALYSIS BRANCH, SUSTAINABLE TECHNOLOGY DIVISION, NRMRL)  

EPA Science Inventory

Non-chemical ecological impacts include those that are caused by physical or biological disturbances. Non-chemical stressors identified by SETAC include ionizing radiation, heat, noise, environmental disturbances (habitat alteration, including changes to biochemical cycling, biod...

397

The kinematics of the diffuse ionized gas in NGC 4666  

NASA Astrophysics Data System (ADS)

Context. The global properties of the interstellar medium with processes such as infall and outflow of gas and a large scale circulation of matter and its consequences for star formation and chemical enrichment are important for the understanding of galaxy evolution. Aims: In this paper we studied the kinematics and morphology of the diffuse ionized gas (DIG) in the disk and in the halo of the star forming spiral galaxy NGC 4666 to derive information about its kinematical properties. Especially, we searched for infalling and outflowing ionized gas. Methods: We determined surface brightness, radial velocity, and velocity dispersion of the warm ionized gas via high spectral resolution (R ? 9000) Fabry-Pérot interferometry. This allows the determination of the global velocity field and the detection of local deviations from this velocity field. We calculated models of the DIG distribution and its kinematics for comparison with the measured data. In this way we determined fundamental parameters such as the inclination and the scale height of NGC 4666, and established the need for an additional gas component to fit our observed data. Results: We found individual areas, especially along the minor axis, with gas components reaching into the halo which we interpret as an outflowing component of the DIG. As the main result of our study, we were able to determine that the vertical structure of the DIG distribution in NGC 4666 is best modeled with two components of ionized gas, a thick and a thin disk with 0.8 kpc and 0.2 kpc scale height, respectively. Therefore, the enhanced star formation in NGC 4666 drives an outflow and also maintains a thick ionized gas layer reminiscent of the Reynold's layer in the Milky Way.

Voigtländer, P.; Kamphuis, P.; Marcelin, M.; Bomans, D. J.; Dettmar, R.-J.

2013-06-01

398

An experimental investigation of mesospheric ionization  

NASA Technical Reports Server (NTRS)

Mesospheric ionization and its variability are examined. Data were obtained primarily by the parachute-borne blunt probe technique conducted in coordinated rocket experiments at White Sands Missile Range, New Mexico and Wallops Island, Virginia. Electrical conductivity measurements and deduced charge density values from ten rocket launches are presented and discussed. Positive ion conductivity and electron density were found to be relatively invariant with height between 45 and 60 km. Variations in positive conductivity of a factor of two and enhancements in negative conductivity by as much as a factor of four were measured by the blunt probe. A simple lumped parameter ion chemistry model is shown to satisfactorily explain the charge density values for the undisturbed lower D-region. Implications of the data in terms of this model are considered. The principal loss mechanism for positive ions in the 45 to 60 km. region is concluded to be dissociative recombination. Electron densities deduced from the conductivity data are explained by detachment involving a minor neutral constituent which is mixed between 65 and 45 km. and then cuts off sharply below 45 km. A correlation study involving blunt probe measurements shows relatively good agreement between variations in positive conductivity and temperature.

Mitchell, J. D.

1973-01-01

399

Chemical analyses of provided samples  

NASA Technical Reports Server (NTRS)

Two batches of samples were received and chemical analysis was performed of the surface and near surface regions of the samples by the surface analysis by laser ionization (SALI) method. The samples included four one-inch optics and several paint samples. The analyses emphasized surface contamination or modification. In these studies, pulsed sputtering by 7 keV Ar+ and primarily single-photon ionization (SPI) by coherent 118 nm radiation (at approximately 5 x 10(exp 5) W/cm(sup 2) were used. For two of the samples, also multiphoton ionization (MPI) at 266 nm (approximately 5 x 10(exp 11) W/cm(sup 2) was used. Most notable among the results was the silicone contamination on Mg2 mirror 28-92, and that the Long Duration Exposure Facility (LDEF) paint sample had been enriched in K and Na and depleted in Zn, Si, B, and organic compounds relative to the control paint.

Becker, Christopher H.

1993-01-01

400

Separation and identification of isomeric acidic degradation products of organophosphorus chemical warfare agents by capillary electrophoresis-ion trap mass spectrometry  

Microsoft Academic Search

Capillary electrophoresis (CE) coupled to ion trap mass spectrometry (MS) was evaluated for the separation and identification of chemical warfare agent degradation products (alkylphosphonic acids and alkyl alkylphosphonic acids). Different analytical parameters were optimized in negative ionization mode such as electrolyte composition (15mM CH3COONH4, pH 8.8), sheath liquid composition (MeOH\\/H2O\\/NH3, 75:25:2, v\\/v\\/v), nebulization and ion trapping conditions. A standard mixture

Mélanie Lagarrigue; Anne Bossée; Arlette Bégos; Anne Varenne; Pierre Gareil; Bruno Bellier

2006-01-01

401

Thermo-chemical dynamics and chemical quasi-equilibrium of plasmas in thermal non-equilibrium  

SciTech Connect

We examine both processes of ionization by electron and heavy-particle impact in spatially uniform plasmas at rest in the absence of external forces. A singular perturbation analysis is used to study the following physical scenario, in which thermal relaxation becomes much slower than chemical reactions. First, electron-impact ionization is investigated. The dynamics of the system rapidly becomes close to a slow dynamics manifold that allows for defining a unique chemical quasi-equilibrium for two-temperature plasmas and proving that the second law of thermodynamics is satisfied. Then, all ionization reactions are taken into account simultaneously, leading to a surprising conclusion: the inner layer for short time scale (or time boundary layer) directly leads to thermal equilibrium. Global thermo-chemical equilibrium is reached within a short time scale, involving only chemical reactions, even if thermal relaxation through elastic collisions is assumed to be slow.

Massot, Marc [Laboratoire EM2C, UPR 288 CNRS - Ecole Centrale Paris (France); Graille, Benjamin [Laboratoire de Mathematiques d'Orsay, UMR 8628 CNRS - Universite Paris-Sud (France); Magin, Thierry E. [Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics (Belgium)

2011-05-20

402

Towards some real applications for negative materials  

NASA Astrophysics Data System (ADS)

The near field technologies, negative index materials (NIM), photonic crystals and plasmonics combined with innovation in high dielectric antennas, wireless systems, and photonic circuits open the prospect of novel antennas, integrated circuits, sensors (chemical, biological and individual molecule), medical scanners, displays and imagers, which have the potential to outperform conventional technology and create many commercial opportunities [A.J. Holden, Inside the Wavelength, Electromagnetics in the Near Field, State of the Science Review for DTI Foresight, UK, February 2004, available at: http://www.foresight.gov.uk/]. A selection of these applications is reviewed and the challenges for the technologies set in context.

Holden, A. J.

2005-12-01

403

Slowing-down and Coulomb capture of negative muons in the hydrogen-helium isotope mixtures  

NASA Astrophysics Data System (ADS)

This paper reports the results of the theoretical study of ionization and Coulomb capture in collisions of slow negative muons with atoms of H, He and molecules of hydrogen isotopes. The cross sections and the kinetic characteristics of these processes in the mixture of molecules of hydrogen isotopes and helium atoms are calculated.

Balashov, V. V.; Dolinov, V. K.; Korenman, G. Ya.; Leonova, S. V.; Moskalenko, I. V.; Popov, V. P.

404

Reversal electron attachment ionizer for detection of trace species  

NASA Technical Reports Server (NTRS)

An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of said electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

Bernius, Mark T. (Inventor); Chutjian, Ara (Inventor)

1990-01-01

405

Reversal electron attachment ionizer for detection of trace species  

NASA Technical Reports Server (NTRS)

An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of the electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

Bernius, Mark T. (inventor); Chutjian, Ara (inventor)

1989-01-01

406

Dynamical saddle vs Coulomb saddle in antiproton impact ionization  

SciTech Connect

The slow Coulomb breakup of a bound pair of particles by charged particle impact is often characterized by the Coulomb saddle located between the two like charges. If the breakup includes an antiproton, however, the particles experience forces on the Coulomb saddle and will tend to drift off the saddle, possibly preventing three particle breakup. There is however a dynamical saddle which eliminates these drift forces among the particles as the system breaks up, analogous to the situation in positron impact ionization. In the case of antiproton impact, the authors thus find a dynamical saddle dominated by the proton-antiproton center of mass with the proton between the two negative charges but about six times closer to the antiproton than the electron. They will present a derivation of the resulting Wannier threshold law and consider possible probes of these fundamental saddles with the antiproton replaced by a negative ion.

Goddard, M.; Feagin J.M. [Univ. of California, Fullerton, CA (United States)

1996-05-01

407

On Negation as Mitigation: The Case of Negative Irony  

ERIC Educational Resources Information Center

Four experiments support the view of negation as mitigation (Giora, Balaban, Fein, & Alkabets, 2004). They show that when irony involves some sizable gap between what is said and what is criticized (He is exceptionally bright said of an idiot), it is rated as highly ironic (Giora, 1995). A negated version of that overstatement (He is not…

Giora, Rachel; Fein, Ofer; Ganzi, Jonathan; Levi, Natalie Alkeslassy; Sabah, Hadas

2005-01-01

408

24. Duplicate negative of an historic negative. 'AERIAL VIEW OF ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

24. Duplicate negative of an historic negative. 'AERIAL VIEW OF AREA 'B' HOLSTON ORDNANCE WORKS.' 1944. #OCMH 4-12.2ASAV3 in Super Explosives Program RDX and Its Composition A, B, & C, Record Group No. 319, National Archives, Washington, D.C. - Holston Army Ammunition Plant, RDX-and-Composition-B Manufacturing Line 9, Kingsport, Sullivan County, TN

409