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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

Comparison of amino acid sequence analysis by electron ionization and negative-ion chemical ionization mass spectrometry.  

PubMed

The positive electron ionization and negative chemical ionization mass spectra of 15 different derivatives of the tripeptide Phe-Ala-Leu have been compared. Total ion currents and ion currents of sequence-characterizing ions have been measured and compared. The negative-ion spectra, using 10% carbon dioxide in argon as moderator gas, proved to be simpler and contained more abundant sequence ions than the positive electron ionization spectra. PMID:2520233

Reinhard, H; Lauber, R; Schlunegger, U P

1989-04-01

3

Negative (CCl sub 4 ) and Positive (NH Sub 3 ) Chemical Ionization of the Explosive Hexanitrostilbene.  

National Technical Information Service (NTIS)

The use of mass spectrometry in the analysis and characterization of explosives and explosive residues has steadily been increasing over the last decade; as a result, positive and negative ion electron impact and chemical ionization mass spectra of many c...

R. O. Yelton

1982-01-01

4

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...

5

Negative chemical ionization studied of human and food chain contamination with xenobiotic chemicals.  

PubMed Central

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 plasma, and human adipose tissue, were cleaned up by one of the following three cleanup procedures: (1) continuous liquid-liquid extraction steam distillation; (2) gel-permeation chromatography; and (3) adsorption on activated carbon followed by elution with toluene. The third procedure was used only for the examination of planar polychlorinated aromatic hydrocarbons in environmental samples. Using these techniques, we have found evidence for contamination of fish samples with polychloronaphthalenes, polychlorostyrenes, polychlorobiphenyls, polychlorodibenzofurans, and polychlorodibenzodioxins among other chemicals. The polychlorodibenzodioxins appeared only in the spectra of extracts of fish obtained from the Tittabawassee River at Midland Michigan. The polychlorodibenzofuran ions appeared in NCI mass spectra of fish that were significantly contaminated (above 2 ppm) with polychlorobiphenyls. Toxic substances occurring in human seminal plasma included pentachlorophenol, hexachlorobenzene, DDT metabolites, and polychlorobiphenyls. We have investigated toxic substances in human seminal plasma because of the apparent decrease in sperm density in U.S. males over the last 30 years. Results of screening human adipose tissue for contamination with xenobiotic chemicals have been largely coincident with result of the EPA human monitoring program. Polychlorobiphenyls, DDT metabolites, nonachlor, and chlordane have appeared in most samples examined. Detection limits for all of these chemicals were of the order of 1 ppb.

Dougherty, R C; Whitaker, M J; Smith, L M; Stalling, D L; Kuehl, D W

1980-01-01

6

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 ...

7

Chemical Ionization  

Microsoft Academic Search

\\u000a Mass spectrometrists have ever been searching for ionization methods softer than EI, because molecular weight determination\\u000a is key for structure elucidation. Chemical ionization (CI) is the first of the so-called soft ionization methods we are going to discuss (cf. Fig. 1.2).

Jürgen H. Gross; Mass Spectrometry

8

Pentachlorophenol in the Environment: Evidence for Its Origin from Commercial Pentachlorophenol by Negative Chemical Ionization Mass Spectrometry.  

National Technical Information Service (NTIS)

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 sp...

D. W. Kuehl R. C. Dougherty

1980-01-01

9

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 ...

10

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 ...

11

Electron impact, electron capture negative ionization and positive chemical ionization mass spectra of organophosphorus flame retardants and plasticizers.  

PubMed

Phosphate esters are important commercial products that have been used both as flame retardants and as plasticizers. To analyze these compounds by gas chromatographic mass spectrometry, it is important to understand the mass spectra of these compounds using various ionization modes. This paper is a systematic overview of the electron impact (EI), electron capture negative ionization (ECNI) and positive chemical ionization (PCI) mass spectra of 13 organophosphate esters. These data are useful for developing and optimizing analytical measurements. The EI spectra of these 13 compounds are dominated by ions such as H4 PO4 (+) , (M?-?Cl)(+) , (M?-?CH2 Cl)(+) or (M)(+) depending on specific chemical structures. The ECNI spectra are generally dominated by (M?-?R)(-) . The PCI spectra are mainly dominated by the protonated molecular ion (M?+?H)(+) . The branching of the alkyl substituents, the halogenation of the substituents and, for aromatic phosphate esters, ortho alkylation of the ring are all significant factors controlling the details of the fragmentation processes. EI provides the best sensitivity for the quantitative measurement of these compounds, but PCI and ECNI both have considerable qualitative selectivity. PMID:23893640

Ma, Yuning; Hites, Ronald A

2013-08-01

12

Congener group patterns of chloroparaffins in marine sediments obtained by chloride attachment chemical ionization and electron capture negative ionization.  

PubMed

Congener group patterns of technical short chain and medium chain chloroparaffins (SCCP and MCCP) were determined by electron capture negative ionization (ECNI) and chloride attachment chemical ionization (CACI) mass spectrometry (MS). In contrast to CACI-MS, congener patterns obtained by ECNI showed always a shift to the next higher chlorinated congener and carbon chain length group. Consequently, the calculated molecular masses and chlorine contents were higher for ECNI (factor 1.10+/-0.03 and 1.09+/-0.03, respectively). ECNI/CACI ratios in sediment samples from the North and Baltic Sea were also slightly higher. However, a more pronounced shift of the congener pattern for a given carbon chain length to congeners with 2-3 more chlorine atoms was observed. SCCP and MCCP concentrations obtained by ECNI-MS were in the range of 8-63ngg(-1) (North Sea) and 22-149ngg(-1) dry weight (Baltic Sea). MCCP levels were highest in all samples (MCCP/SCCP factor 1.1-3.2). PMID:16412495

Hüttig, Jana; Oehme, Michael

2006-01-18

13

Determination of dexamethasone in urine by gas chromatography with negative chemical ionization mass spectrometry.  

PubMed

Dexamethasone, as some other synthetic corticosteroids, is licensed for therapy in veterinary practice, but its misuse as a growth promotor, often in combination with beta-agonists, is forbidden. In this report an analytical method is described for the detection and confirmation of very low concentrations of dexamethasone in urine. The influence of enzymatic hydrolysis time of samples with glucuronidase was studied. The proposed method consisted of the enzymatic hydrolysis of urine samples, which were then extracted and concentrated using solid-phase cartridges with mixed reversed-phase materials (OASIS). No further clean-up step was found to be necessary. Eluates were derivatized following a previously described method [Analyst 119 (1994) 2557]. Detection, identification and quantification of residues of this compound was carried out by gas chromatography with mass spectrometry in the negative chemical ionization mode. The proposed procedure permits the determination of dexamethasone in urine at levels as low as 0.2 ng ml(-1) PMID:12668079

Huetos Hidalgo, Olga; Jiménez López, Manuel; Ajenjo Carazo, Elisa; San Andrés Larrea, Manuel; Reuvers, Thea B A

2003-05-01

14

Determination of nitrated polycyclic aromatic hydrocarbons by fused silica capillary gas chromatography\\/negative ion chemical ionization mass spectrometry  

Microsoft Academic Search

Gas chromotography\\/electron capture negative ion chemical ionization mass spectrometry is shown to be a very sensitive and selective determination method for nitrated polycyclic aromatic hydrocarbons (PAH). The detection limit was 1 pg injected to the GC column using single ion monitoring. The mass spectra are characterized by an intense molecular ion, the base peak in all spectra. The second most

Thomas. Ramdahl; Kjell. Urdal

1982-01-01

15

Negative ion chemical ionization gas chromatography/mass spectrometry of valproic acid metabolites.  

PubMed

A negative ion chemical ionization (NICI) gas chromatographic/mass spectrometric method is described for the identification of 15 valproic acid (VPA) metabolites as their pentafluorobenzyl derivatives. Samples analyzed were serum, urine and saliva taken from a volunteer on VPA at steady state and also given selected doses of (2H6)VPA. Metabolite peaks were identified by comparison to synthetic standards. All the metabolites, like the parent drug, produced abundant [M - 181]- ions, except 3-keto VPA, which gave an [M - 181 - CO2]- ion. Using the NICI method, two new VPA metabolites were identified. One of these metabolites was characterized as 4'-keto-2-ene VPA by synthesis, while the second one appeared to be a positional isomer of 4'-keto-2-ene VPA. The sensitivity of the method was also sufficient to detect metabolites of VPA in saliva. The ratio of the levels of (Z)-2-ene VPA to (E)-2-ene VPA was much greater in saliva than in serum, suggesting stereoselective plasma protein binding or transport of these two metabolites. The lower limit of detection for the quantification of VPA in serum or saliva was 2 ng ml-1. PMID:2508808

Kassahun, K; Burton, R; Abbott, F S

1989-10-01

16

Negative (CCl/sub 4/) and positive (NH/sub 3/) chemical ionization of the explosive hexanitrostilbene  

SciTech Connect

The use of mass spectrometry in the analysis and characterization of explosives and explosive residues has steadily been increasing over the last decade; as a result, positive and negative ion electron impact and chemical ionization mass spectra of many commonly encountered explosives have been reported by several workers in the open literature. The nitro-aromatic explosive hexanitrostilbene (HNS) is finding increasing application because of its low sensitivity to shock, friction, and impact, combined with its excellent stability at elevated temperatures (M.P. > 315/sup 0/C); however, mass spectrometric data on this relatively low vapor pressure, high temperature explosive have not been thus far reported. This investigation has been directed toward obtaining a suitable mass spectrum for HNS by examining positive and negative electron impact (EI) and chemical ionization (CI) techniques.

Yelton, R.O.

1982-01-01

17

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

Microsoft Academic Search

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

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

1996-01-01

18

The background atmospheric concentrations of cyclic perfluorocarbon tracers determined by negative ion-chemical ionization mass spectrometry  

Microsoft Academic Search

The background atmospheric mixing ratios for a range of cyclic perfluorocarbons (cyclic-PFCs), widely used in atmospheric dispersion studies, have been measured by gas chromatography-mass spectrometry in negative ion-chemical ionization mode. Background concentrations range from <1fll?1 to >10fll?1, where femtolitre is expressed as parts in 1015 (ppqv). Because of their very long atmospheric lifetimes (>3000yr) the present day concentrations represent the

P. G. Simmonds; B. R. Greally; S. Olivier; G. Nickless; K. M. Cooke; R. N. Dietz

2002-01-01

19

Extraction of explosives from soil followed by gas chromatography-mass spectrometry analysis with negative chemical ionization.  

PubMed

A new, simple and accurate method for extraction of explosives from soil was developed and validated. The method includes one hour gentle extraction of compounds from soil in acetonitrile:dichloromethane 50:50 at 30°C. Further analysis was made with GC-MS using cool on-column injection and negative chemical ionization. The method increased the recovery of the more volatile products, generated higher accuracy and was extensively time-saving compared to the conventional EPA (US Environmental Protection Agency) 8330 method. Applications are demonstrated on commercial reference materials. PMID:22226557

Holmgren, Erik; Ek, Stefan; Colmsjö, Anders

2011-12-13

20

Fast gas chromatography and negative-ion chemical ionization tandem mass spectrometry for forensic analysis of cannabinoids in whole blood  

Microsoft Academic Search

The present work describes a fast gas chromatography\\/negative-ion chemical ionization tandem mass spectrometric assay (Fast GC\\/NICI-MS\\/MS) for analysis of tetrahydrocannabinol (THC), 11-hydroxy-tetrahydrocannabinol (THC-OH) and 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH) in whole blood. The cannabinoids were extracted from 500?L of whole blood by a simple liquid–liquid extraction (LLE) and then derivatized by using trifluoroacetic anhydride (TFAA) and hexafluoro-2-propanol (HFIP) as fluorinated agents. Mass spectrometric

Aurélien Thomas; Christèle Widmer; Gérard Hopfgartner; Christian Staub

2007-01-01

21

Gas chromatography negative ion chemical ionization mass spectrometry: application to the detection of alkyl nitrates and halocarbons in the atmosphere.  

PubMed

Alkyl nitrates and very short-lived halocarbon species are important atmospheric trace gas species that are present in the low to sub parts per trillion concentration range. This presents an analytical challenge for their detection and quantification that requires instrumentation with high sensitivity and selectivity. In this paper, we present a new in situ gas chromatograph negative ion chemical ionization mass spectrometer (GC/NICI-MS) coupled to a non-cryogen sample pre-concentration system. This instrument, with detection limits of <0.01 ppt, is capable of detecting and quantifying a large suite of alkyl nitrate and halocarbon species with high sensitivity and precision. The effects of ion source temperature and reagent gas pressure on the ionization efficiency of the NICI mode are investigated and the results are used to optimize the sensitivity. The NICI mode is compared to the more frequently used electron impact (EI) ionization and the enhancements in sensitivity are presented for all the calibrated compounds. PMID:18586255

Worton, David R; Mills, Graham P; Oram, David E; Sturges, William T

2008-06-18

22

Analysis of tryptamine at the femtomole level in tissue using negative ion chemical ionization gas chromatography-mass spectrometry.  

PubMed

An ultra sensitive method for the detection of tryptamine, an endogenous amine in mammalian neuronal systems, at the femtomole level has been developed using negative chemical ionization gas chromatography-mass spectrometry (NCI-GC-MS). The amine is converted into a perfluorinated spirocyclic derivative, e.g. 1-pentafluoro-2-methylenepyrrolidine-3-spiro-3'-(3H-indole) which is detected using selected-ion monitoring of the (M-2HF) ions of the endogenous and deuterated internal standard compounds. Two mass spectrometers were compared; they gave minimum detectable quantities from tissue samples of 40 pg (VG-7070F) and 0.9 pg (VG-70S) respectively. These detection levels are approximately 5-200 times lower than have been obtained by previous MS methods. PMID:3403664

Durden, D A; Boulton, A A

1988-05-25

23

QUANTITATION OF MONOSACCHARIDE ISOTOPIC ENRICHMENT IN PHYSIOLOGIC FLUIDS BY ELECTRON IONIZATION OR NEGATIVE CHEMICAL IONIZATION GC/MS USING DI-O-ISOPROPYLIDENE DERIVATIVES.  

Technology Transfer Automated Retrieval System (TEKTRAN)

The aldonitrile pentaacetate and other derivatives lack ions in the electron ionization (EI) spectra possessing an intact hexose structure and thus must be analyzed by chemical ionization GC/MS in order to study multiple isotopomers. We report methods for quantitation of hexose di-O-isopropylidene a...

24

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...

25

Isomer-specific determination of hexachlorodibenzo-p-dioxins by oxygen negative chemical ionization mass spectrometry, gas chromatography, and high-pressure liquid chromatography  

Microsoft Academic Search

All ten hexachlorodibenzo-p-dioxin (HCDD) isomers, prepared by micropyrolysis of chlorophenates, were studied by using mass spectrometry, gas chromatography, and high-pressure liquid chromatography. Of several ionization modes studied, oxygen negative chemical ionization was the most suitable for isomer identification. This technique enabling isomer specific identification to be carried out was applied to hexachlorodioxin impurities in pentachlorophenol samples and detected small amounts

Walter F. Miles; Narine P. Gurprasad; Greg P. Malis

1985-01-01

26

Structural determination of zinc dithiophosphates in lubricating oils by gas chromatography–mass spectrometry with electron impact and electron-capture negative ion chemical ionization  

Microsoft Academic Search

Pentafluorobenzyl ester derivatives were used to identify zinc dialkyldithiophosphates and diaryldithiophosphates anti-wear engine oil additives by GC–electron impact ionization (EI) MS and GC–electron-capture negative ion chemical ionization (ECNCI) MS analysis. GC–EI-MS of the dialkyldithiophosphate–pentafluorobenzyl derivatives afforded characteristic fragment ions corresponding to the cleavage of one and two alkyl radicals. In most cases, information was only obtained on one alkyl chain.

M Becchi; F Perret; B Carraze; J. F Beziau; J. P Michel

2001-01-01

27

Confirmation of clorsulon residues in cattle kidney by capillary gas chromatography-negative-ion chemical-ionization mass spectrometry.  

PubMed

A confirmatory assay for residues of the anthelmintic agent clorsulon [4-amino-6-(trichloroethenyl)-1,3-benzenedisulfonamide] in cattle kidney tissue has been developed. The assay involves isolation of a drug-containing fraction by solvent extraction, methylation of the analyte, and fused-silica capillary column gas chromatography-negative-ion chemical-ionization mass spectrometry of the pentamethyl derivative of clorsulon. The intensities of four negative ions [m/z 406 and 408 (trichloro species) and m/z 413 and 415 (dichloro species)] are monitored. Confirmation of the presence of drug in an analyte requires that all four ions appear at the appropriate retention time with their intensity ratios within 10-15% of those arising from analysis of the reference standard, methylated clorsulon; the lower limit of detection is 3 ppb. Quantification of the drug is based on the intensity of the m/z 406 ion. Identification and quantification of residues by the gas chromatographic-mass spectrometric assay gave results in good agreement with those obtained with an electron-capture gas chromatographic assay. PMID:3654857

Wehner, T A; Wood, J S; Walker, R; Downing, G V; Vandenheuvel, W J

1987-07-24

28

Chemically induced hyperthermal surface ionization  

SciTech Connect

Hyperthermal beams of cyclohexane and carbon tetrachloride were scattered from a 2% W-Th filament. Chlorine negative ions generated by chemically induced hyperthermal surface ionization were monitored by quadrupole mass spectrometer. The surface temperature of the filament was 2400K. (AIP)

Danon, A.; Amirav, A. (School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat Aviv 69978, Israel (IL))

1990-06-01

29

Negative ion chemical ionization mass spectrometric method for confirmation of identity of aflatoxin B1: collaborative study.  

PubMed

An interlaboratory study of a negative ion chemical ionization mass spectrometric (MS) confirmation procedure for aflatoxin B1 was conducted in laboratories in the United States, England, and West Germany. Twelve partially purified, dry film extracts from naturally and artificially contaminated roasted peanuts, cottonseed, and ginger root containing varying quantities of aflatoxin B1 were distributed to the participating laboratories. The extracts required additional cleanup before MS analysis, using either an acidic alumina column and preparative thin layer chromatography (TLC) or a 2-dimensional TLC procedure. Recovery of purified aflatoxin B1 was influenced by the degree of recovery of sample from acid alumina and/or the TLC plate and incomplete elution of aflatoxin B1 from silica gel. Factors affecting MS confirmation included the purity and recovery of aflatoxin and MS instrument sensitivity. Aflatoxin B1 identity was confirmed in 19.5, 90.9, and 100% of samples containing less than 5, 5-10, and greater than 10 ng aflatoxin B1/g product, respectively, by solid probe introduction using full mass scans. The MS method has been adopted official first action. PMID:3928591

Park, D L; Diprossimo, V; Abdel-Malek, E; Trucksess, M W; Nesheim, S; Brumley, W C; Sphon, J A; Barry, T L; Petzinger, G

30

Determination of nitrated polycyclic aromatic hydrocarbons by fused silica capillary gas chromatography/negative ion chemical ionization mass spectrometry  

SciTech Connect

Gas chromotography/electron capture negative ion chemical ionization mass spectrometry is shown to be a very sensitive and selective determination method for nitrated polycyclic aromatic hydrocarbons (PAH). The detection limit was 1 pg injected to the GC column using single ion monitoring. The mass spectra are characterized by an intense molecular ion, the base peak in all spectra. The second most abundant ions were (M - 16)/sup -/ and (M - 30)/sup -/ for mono- and dinitro-PAH, respectively. The NO/sub 2//sup -/ ion (m/z 46) is observed in most spectra. There are few differences in the mass spectra of various isomeric compounds. The pressure and the temperature in the ion source had little influence on the mass spectra and sensitivity within the limits tested. The method is demonstrated on a synthetic mixture containing nitro-PAH, and on a toluene extract of a formerly commercial carbon black. The application to urban air particulate extracts is discussed. 4 figures, 4 tables.

Ramdahl, T.; Urdal, K.

1982-11-01

31

Determination of polychlorinated biphenyls in serum using gas chromatography-mass spectrometry with negative chemical ionization for exposure estimation.  

PubMed

A sensitive and selective method for the determination of 24 polychlorinated biphenyls (PCBs) by gas chromatography-mass spectrometry with negative chemical ionization (GC-MS-NCI) was applied for the recent needs of occupational exposure in waste incineration. The three most abundant ions were used in determining compounds with at least five chlorine atoms in the PCB molecule. Selecting ions Cl(35) and Cl(37) for di-, tri-, and tetrachlorinated PCBs resulted in reliable quantification of these compounds. The detection limits for the 24 individual compounds varied from 0.01 to 0.08 microg/l. The recovery of the method was 113+/-16%. Stability tests showed no degradation of the compounds studied during 6 weeks. The sum of 24 PCB compounds measured from the sera of workers in a disposal plant was 1.9-10.9 microg/l, and 0.3-3.0 microg/l for controls, respectively. The mean proportion of the low chlorinated PCB compounds (with four or less chlorine atoms) was 20% for workers in the disposal plant and 14% for the controls. PMID:12798172

Kontsas, Helena; Pekari, Kaija

2003-07-01

32

The simultaneous separation and determination of chloropropanols in soy sauce and other flavoring with gas chromatography-mass spectrometry in negative chemical and electron impact ionization modes  

Microsoft Academic Search

Both gas chromatography-mass spectrometry in electron ionization (GC-MS-EI) and negative chemical ionization (GC-MS-NCI) modes are reported in this paper for the simultaneous determination of 1,3-dichloropropan-2-ol (1,3-DCP), 2,3-dichloropropan-1-ol (2,3-DCP), 3-chloropropane-1,2-diol (3-MCPD) and 2-chloropropane-1,3-diol (2-MCPD) in soy sauce and other flavoring. D5-3-MCPD (for 3-MCPD and 2-MCPD) and d5-1,3-DCP (for 1,3-DCP and 2,3-DCP) were used as the deuterium isotopic labelled internal standards. The

Xiaomin Xu; Yiping Ren; Pinggu Wu; Jianlong Han; Xianghong Shen

2006-01-01

33

Quantification of Neurosteroids in Rat Plasma and Brain Following Swim Stress and Allopregnanolone Administration Using Negative Chemical Ionization Gas Chromatography\\/Mass Spectrometry  

Microsoft Academic Search

A simplified method for the quantitative analysis of neurosteroids in rat plasma and brain is described. The method uses negative chemical ionization gas chromatography\\/mass spectrometry and involves the synthesis of pentafluorobenzyloxime\\/trimethylsilyl ether derivatives with excellent chromatographic and electron-capturing properties. Deuterium-labeled analogs of the steroids of interest were synthesized and used as internal standards. The steroids (allopregnanolone, epiallopregnanolone, pregnenolone, testosterone, and

Monique Vallée; Jeffery D. Rivera; George F. Koob; Robert H. Purdy; Robert L. Fitzgerald

2000-01-01

34

Analytical method development for the determination of synthetic pyrethroid insecticides in soil by gas chromatography-mass spectrometry operated in negative-ion chemical-ionization mode  

Microsoft Academic Search

An effective analytical method for the simultaneous determination of five synthetic pyrethroid insecticides in soil is developed and method performance data presented. The pyrethroid residues were extracted with hexane-dichloromethane in an ultrasonic bath. The extract was cleaned up on a Florisil column prior to determination by gas chromatography—negative-ion chemical ionization mass spectrometry (GC-NICI-MS) in selected-ion monitoring (SIM) mode. The highest

M. Yasin; P. J. Baugh; G. A. Bonwick; D. H. Davies; P. Hancock; M. Leinoudi

1996-01-01

35

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  

Microsoft Academic Search

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

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

2009-01-01

36

Determination of delta 9-tetrahydrocannabinol-11-oic acid in urine as its pentafluoropropyl-pentafluoropropionyl derivative by GC/MS utilizing negative ion chemical ionization.  

PubMed

A rapid and sensitive GC/MS method for the determination of delta 9-tetrahydrocannabinol-11-oic acid in urine is presented. Enzymically hydrolyzed urine was extracted with hexane/ethyl ether followed by a one-step derivatization procedure with a mixture of pentafluoropropionic anhydride and pentafluoropropanol. By using negative ion chemical ionization and selected ion monitoring, a 200-fold higher detectability was observed, compared with El or positive ion chemical ionization under the conditions used. Samples were analyzed with split injection on a fused silica capillary column with a total analysis time of less than four minutes. A deuterium labelled analogue was used as internal standard and the precision for the overall method was measured to 3.4% for a sample concentration of 230 ng/mL, and to 6.7% for 3 ng/mL. The minimum detectable amount was below 1 ng/mL. PMID:6314044

Karlsson, L; Jonsson, J; Aberg, K; Roos, C

37

[Multiresidue determination of organophosphorus pesticide residues in vegetables and fruit by gas chromatography-negative ion chemical ionization-mass spectrometry].  

PubMed

An analytical method of gas chromatography coupled with negative ion chemical ionization-mass spectrometry for simultaneous determination of nine organophosphorus pesticide residues in vegetables and fruit has been developed, and the negative ions structure and partition mechanism of the nine organophosphorus pesticides were interpreted. Meanwhile, the matrix effect for sample analysis was discussed, and matrix-matched calibration for quantification was introduced to reduce the matrix effect in this method. Pesticides were extracted from sample with ethyl acetate in an ultrasonic bath, then determined by gas chromatography-mass spectrometry operated in negative chemical ionization mode and quantified in selective ion monitoring mode, and ethion was used as an internal standard. The detection limits of the method were 0.12-1.0 microg/kg for the nine organophosphorus pesticides, and the relative coefficients were higher than 0.9993. A blank sample (tomato) was spiked at 100, 400, 800 microg/kg for each pesticide, and the recoveries were determined to be from 78% to 126% with relative standard deviations from 0.58% to 14.7% for the pesticides. PMID:16929836

Lin, Zhuguang; Fan, Yulan; Ma, Yu; Jin, Zhen; Tan, Jun; Chen, Meiyu; Chen, Zhaobin; Tu, Fengzhang; Liu, Yong

2006-05-01

38

Trace level detection of chlorinated paraffins in biological and environmental samples, using gas chromatography/mass spectrometry with negative-ion chemical ionization.  

PubMed

A method is described for detection of chlorinated paraffins (CPs) in biological and environmental samples. Sample preparation includes sulfuric acid treatment followed by adsorption chromatography on alumina, which yields the CPs in one fraction that is almost free of interfering material. Using gas chromatography/mass spectrometry with negative-ion chemical ionization, the limit of detection is 5 ng (corresponding to the lower ppb range). CP levels of 30 ppm, 200 ppb, and 5 ppb were found in sewage sludge, human fat, and sediment, respectively. PMID:4019363

Schmid, P P; Müller, M D

39

Measurements of gas-phase inorganic and organic acids from biomass fires by negative-ion proton-transfer chemical-ionization mass spectrometry  

Microsoft Academic Search

Emissions from 34 laboratory biomass fires were investigated at the combustion facility of the U.S. Department of Agriculture Fire Sciences Laboratory in Missoula, Montana. Gas-phase organic and inorganic acids were quantified using negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS), open-path Fourier transform infrared spectroscopy (OP-FTIR), and proton-transfer-reaction mass spectrometry (PTR-MS). NI-PT-CIMS is a novel technique that measures the mass-to-charge ratio (m\\/z)

Patrick Veres; James M. Roberts; Ian R. Burling; Carsten Warneke; Joost de Gouw; Robert J. Yokelson

2010-01-01

40

A new measurement technique of peroxyacetyl nitrate at parts per trillion by volume levels: Gas chromatography\\/negative ion chemical ionization mass spectrometry  

Microsoft Academic Search

A new technique for measuring peroxyacetyl nitrate (PAN) at parts per trillion by volume (pptv) levels has been developed using gas chromatography with negative ion chemical ionization mass spectrometry (GC\\/NICI MS). Four fragment ions, CH3C(O)O- (mass-to-charge ratios (m\\/z)=59), NO3-(m\\/z=62), CH3C(O)OO-(m\\/z=75), and NO2-(m\\/z=46), were identified by NICI mass spectra. NO3-(m\\/z=62) was used in selected ion monitoring (SIM) mode among these fragment

Hiroshi Tanimoto; Jun Hirokawa; Yoshizumi Kajii; Hajime Akimoto

1999-01-01

41

Structural determination of zinc dithiophosphates in lubricating oils by gas chromatography-mass spectrometry with electron impact and electron-capture negative ion chemical ionization.  

PubMed

Pentafluorobenzyl ester derivatives were used to identify zinc dialkyldithiophosphates and diaryldithiophosphates antiwear engine oil additives by GC-electron impact ionization (EI) MS and GC-electron-capture negative ion chemical ionization (ECNCI) MS analysis. GC-EI-MS of the dialkyldithiophosphate-pentafluorobenzyl derivatives afforded characteristic fragment ions corresponding to the cleavage of one and two alkyl radicals. In most cases, information was only obtained on one alkyl chain. Additional and complete information was obtained with retention time indices using synthetic derivatives and with GC-ECNCI-MS analysis. ECNCI afforded characteristic dithiophosphate anions which allowed the determination of the total number of carbon atoms in the alkyl radicals. The diastereoisomer mixtures of 2-hydroxy-sec.-alkyl radicals were completely separated on GC analysis. PMID:11206788

Becchi, M; Perret, F; Carraze, B; Beziau, J F; Michel, J P

2001-01-01

42

Quantitative measurement of delta 9-tetrahydrocannabinol and two major metabolites in physiological specimens using capillary column gas chromatography negative ion chemical ionization mass spectrometry.  

PubMed

delta 9-Tetrahydrocannabinol and two of its metabolites, 11-hydroxy-delta 9-tetrahydrocannabinol and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol, can be measured in a single 1-ml sample of blood, plasma, or urine by a new assay which combines a relatively rapid extraction procedure with capillary column gas chromatography and negative ion chemical ionization mass spectrometry. Deuterium-labeled analogs of each cannabinoid are added to the physiological specimen as internal standards. Two extracts are obtained from each sample: a neutral fraction containing delta 9-tetrahydrocannabinol and 11-hydroxy-delta 9-tetrahydrocannabinol, and an acid fraction containing 11-nor-9-carboxy-delta 9-tetrahydrocannabinol. The neutral fraction is derivatized by treatment with trifluoroacetic anhydride; the acid fraction is first treated with BF3-methanol followed by reaction with trifluoroacetic anhydride. Under electron-capture chemical ionization conditions the derivatized delta 9-tetrahydrocannabinol and 11-nor-9-carboxy-delta 9-tetrahydrocannabinol give abundant molecular anions ideally suited for selected ion monitoring. The negative ion chemical ionization spectrum of the HO-THC-trifluoroacetate shows no molecular anion. Consequently, quantitation of the hydroxy metabolite is achieved by monitoring a fragment ion formed by loss of CF3CO2 from its molecular anion. The limits of reliable measurement are judged to be 0.1 ng ml-1 for 11-nor-9-carboxy-delta 9-tetrahydrocannabinol, 0.2 ng ml-1 for delta 9-tetrahydrocannabinol and 0.5 ng ml-1 for 11-hydroxy-delta 9-tetrahydrocannabinol. Four examples are given of the application of the assay to the analysis of specimens of medico-legal importance. PMID:6305440

Foltz, R L; McGinnis, K M; Chinn, D M

1983-05-01

43

Perfluoroalkyl ketones: novel derivatization products for the sensitive determination of fatty acids by gas chromatography/mass spectrometry in electron impact and negative chemical ionization modes.  

PubMed

Analytically useful pentafluoro ketone derivatives of fatty acids are described. The gas chromatographic/mass spectrometric characteristics of these new derivatives are compared with those of methyl, trimethylsilyl and pentafluorobenzyl esters. Pentafluoro ketones exhibit excellent chromatographic properties and significantly shorter chromatographic retention times than these other esters. The electron impact mass spectra of these new compounds show informative acylium ions, whose intensity decreases with the degree of unsaturation of the parent fatty acid. The formation of strong and informative fragment ions in negative chemical ionization (CH(4)) mass spectra of pentafluoro ketone derivatives allows the detection and the characterization (length of the chain and number of double bonds) of fatty acids at trace levels (femtomole), even in the case of polyunsaturated compounds. The scope and limitations of this new derivatization technique are also discussed. PMID:10844732

Aubert, C; Rontani, J F

2000-01-01

44

Determination of misoprostol free acid in human breast milk and serum by gas chromatography/negative ion chemical ionization tandem mass spectrometry.  

PubMed

To study an expected transition of misoprostol from human blood into breast milk, a novel method for the determination of its active metabolite misoprostol acid (MPA) was developed. MPA was determined in serum and breast milk samples by an isotope dilution assay using gas chromatography/negative ion chemical ionization tandem mass spectrometry (GC/NICI-MS/MS). After addition of (15S)-15-methylprostaglandin E(2) (15-methyl-PGE(2)) as an internal standard, MPA was extracted from both matrices using a reversed-phase cartridge. The prostanoids were derivatized with O-2,3,4,5,6-pentafluorobenzylhydroxylamine hydrochloride (PFBHA) and 2,3,4,5,6-pentafluorobenzyl bromide (PFBB) to the pentafluorobenzyl oxime (PFBO)-pentafluorobenzyl ester (PFB) derivatives. The sample was subjected to thin-layer chromatography with ethyl acetate-hexane (1 : 1 (v/v)) as the developing solvent. The corresponding zone was extracted. After derivatization to the trimethylsilyl ether, MPA was determined by GC/NICI-MS/MS using the [molecule (M) - pentafluorobenzyl (PFB)](-) ([P](-)) ions as precursor in the negative ion chemical ionization mode. The product ions used for quantification were [P - 2TMSOH - C(6)F(5)CH(2)OH](-) (MPA) and [P - 2TMSOH - C(6)F(5)CH(2)OH - CO(2)](-)(15-methyl-PGE(2)), respectively. The limit of quantification for MPA was approximately 1 pg ml(-1) in breast milk and serum samples. The correlation coefficients of the calibration curves for MPA were r > 0.997 in the 0.5-2000 pg ml(-1) range for both tested matrices. PMID:12271435

Watzer, Bernhard; Seyberth, Hannsjörg W; Schweer, Horst

2002-09-01

45

The simultaneous separation and determination of chloropropanols in soy sauce and other flavoring with gas chromatography-mass spectrometry in negative chemical and electron impact ionization modes.  

PubMed

Both gas chromatography-mass spectrometry in electron ionization (GC-MS-EI) and negative chemical ionization (GC-MS-NCI) modes are reported in this paper for the simultaneous determination of 1,3-dichloropropan-2-ol (1,3-DCP), 2,3-dichloropropan-1-ol (2,3-DCP), 3-chloropropane-1,2-diol (3-MCPD) and 2-chloropropane-1,3-diol (2-MCPD) in soy sauce and other flavoring. D(5)-3-MCPD (for 3-MCPD and 2-MCPD) and d(5)-1,3-DCP (for 1,3-DCP and 2,3-DCP) were used as the deuterium isotopic labelled internal standards. The feasibility of using heptafluorobutyric anhydride modified with triethylamine (HFBA-Et(3)N) as a new derivatization reagent to replace heptafluorobutyrylimidazole (HFBI) is proposed. Liquid/liquid extraction with hexane was introduced for high lipid content samples. A small survey was carried out of soy sauces (103 samples) and instant noodles (45 samples) and the applicability of GC-MS-NCI and GC-MS-EI was assessed in these different matrices. PMID:16449052

Xu, Xiaomin; Ren, Yiping; Wu, Pinggu; Han, Jianlong; Shen, Xianghong

2006-02-01

46

Chemical Protection Against Ionizing Radiation.  

National Technical Information Service (NTIS)

The scientific literature on radiation-protective drugs is reviewed. Emphasis is placed on the mechanisms involved in determining the sensitivity of biological material to ionizing radiation and mechanisms of chemical radioprotection. In Section I, the ty...

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

1984-01-01

47

Comparison of Gas Chromatography-Mass Spectrometry and Gas Chromatography-Tandem Mass Spectrometry with Electron Ionization and Negative-Ion Chemical Ionization for Analyses of Pesticides at Trace Levels in Atmospheric Samples  

PubMed Central

A comparison of detection limits of gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) with gas chromatography-tandem mass spectrometry (GC-MS/MS) in selected reaction monitoring (SRM) mode with both electron ionization (EI) and negative-ion chemical ionization (NCI) are presented for over 50 pesticides ranging from organochlorines (OCs), organophosphorus pesticides (OPs) and pre-emergent herbicides used in the Canadian prairies (triallate, trifluralin, ethalfluralin). The developed GC-EI/SIM, GC-NCI/SIM, and GC-NCI/SRM are suitable for the determination of pesticides in air sample extracts at concentrations <100 pg ?L?1 (<100 pg m?3 in air). No one method could be used to analyze the range of pre-emergent herbicides, OPs, and OCs investigated. In general GC-NCI/SIM provided the lowest method detection limits (MDLs commonly 2.5–10 pg ?L?1) along with best confirmation (<25% RSD of ion ratio), while GC-NCI/SRM is recommended for use where added selectivity or confirmation is required (such as parathion-ethyl, tokuthion, carbofenothion). GC-EI/SRM at concentration <100 pg ?L?1 was not suitable for most pesticides. GC-EI/SIM was more prone to interference issues than NCI methods, but gave good sensitivity (MDLs 1–10 pg ?L?1) for pesticides with poor NCI response (OPs: sulfotep, phorate, aspon, ethion, and OCs: alachlor, aldrin, perthane, and DDE, DDD, DDT).

Raina, Renata; Hall, Patricia

2008-01-01

48

Comparison of gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry with electron ionization and negative-ion chemical ionization for analyses of pesticides at trace levels in atmospheric samples.  

PubMed

A comparison of detection limits of gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) with gas chromatography-tandem mass spectrometry (GC-MS/MS) in selected reaction monitoring (SRM) mode with both electron ionization (EI) and negative-ion chemical ionization (NCI) are presented for over 50 pesticides ranging from organochlorines (OCs), organophosphorus pesticides (OPs) and pre-emergent herbicides used in the Canadian prairies (triallate, trifluralin, ethalfluralin). The developed GC-EI/SIM, GC-NCI/SIM, and GC-NCI/SRM are suitable for the determination of pesticides in air sample extracts at concentrations <100 pg microL(-1) (<100 pg m(-3) in air). No one method could be used to analyze the range of pre-emergent herbicides, OPs, and OCs investigated. In general GC-NCI/SIM provided the lowest method detection limits (MDLs commonly 2.5-10 pg microL(-1)) along with best confirmation (<25% RSD of ion ratio), while GC-NCI/SRM is recommended for use where added selectivity or confirmation is required (such as parathion-ethyl, tokuthion, carbofenothion). GC-EI/SRM at concentration <100 pg microL(-1) was not suitable for most pesticides. GC-EI/SIM was more prone to interference issues than NCI methods, but gave good sensitivity (MDLs 1-10 pg microL(-1)) for pesticides with poor NCI response (OPs: sulfotep, phorate, aspon, ethion, and OCs: alachlor, aldrin, perthane, and DDE, DDD, DDT). PMID:19609395

Raina, Renata; Hall, Patricia

2008-09-09

49

Studies on steroids. CCXXXVIII. Determination of bile acids in liver tissue by gas chromatography-mass spectrometry with negative ion chemical ionization detection.  

PubMed

A method for the determination of bile acids in 2-10 mg of human liver tissue by gas chromatography (GC) in combination with negative ion chemical ionization (NICI) mass spectrometry is described. Unconjugated, glycine- and taurine-conjugated bile acids labelled with 18O and 2H were used as internal standards. The preparation of these compounds was attained by the exchange reaction of the carbonyl group with H218O, followed by metal hydride reduction. Bile acids in solubilized liver tissue were extracted with a Sep-Pak C18 cartridge, separated into the unconjugated, glycine- and taurine-conjugated fractions by ion-exchange chromatography on piperidinohydroxypropyl-Sephadex LH-20 and then derivatized to the pentafluorobenzyl ester-dimethylethylsilyl ethers. Subsequent resolution of each fraction into lithocholate, deoxycholate, chenodeoxycholate, ursodeoxycholate and cholate was attained by GC on a cross-linked 5% phenylmethyl silicone fused-silica capillary column where bile acids were monitored with a characteristic carboxylate anion [M - 181]-in the NICI mode using isobutane as a reagent gas. The newly developed method was applied to the quantitation of bile acids in liver tissue with satisfactory sensitivity and reliability. PMID:3243844

Goto, J; Miura, H; Inada, M; Nambara, T; Nagakura, T; Suzuki, H

1988-10-28

50

Quantitation of the tetrachloroethylene metabolite N-acetyl-S-(trichlorovinyl)cysteine in rat urine via negative ion chemical ionization gas chromatography/tandem mass spectrometry.  

PubMed

A sensitive and selective negative ion chemical ionization gas chromatographic/tandem mass spectrometric (NICI GC/MS/MS) method was developed for the determination of the tetrachlorethylene metabolite, N-acetyl-S-(trichlorovinyl)cysteine (TCVC), in rat urine. Urine samples were fortified with a 13C,D2-analog of TCVC, acidified and extracted with ethyl acetate. The extract were derivatized with methanolic HCl, and the resulting methyl esters analyzed via NICI GC/MS/MS. Detection of the TCVC analogs was performed by monitoring the Cl- product ion of M-Cl2C2HS-. The limit of detection for TCVC by this method was estimated to be 0.1 ng ml-1 urine (3 x noise). The quantitation limit was determined to be 0.3 ng TCVC per milliliter of urine. The method was found to be linear for TCVC concentrations from 0.3 to 104 ng ml-1 urine. Relative recovery of TCVC from urine ranged from 95.4% to 108.5%. Additional data are given for GC/MS and GC/MS/MS analysis of the pentafluoro-benzyl ester derivative of TCVC. Data are also presented for the isolation and analysis of this compound obtained from dosed rats. PMID:7811758

Bartels, M J

1994-11-01

51

Analysis of 5-methoxytryptamine at the femtomole level in the rat and quail brain by gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry.  

PubMed

A sensitive method for the measurement of endogenous 5-methoxytryptamine in brain tissue has been developed using capillary column gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry. 5-Methoxytryptamine was first converted to N-[2H3]acetyl-5-methoxytryptamine by reaction with hexa-deuterated acetic anhydride, followed by reaction with pentafluoropropionic anhydride to yield the highly electron-capturing 3,3'-spirocyclic pentafluoro-propionyl indolenine derivative. Quantitative analysis was carried out by selected-ion monitoring of the [M-HF].- and [M-HF-DF].- ion intensity of the 3.3'-spirocyclic pentafluoropropionyl indolenine derivative, using 5-methoxy-[alpha, alpha, beta, beta-2H4]tryptamine as the internal standard. The presence of 5-methoxytryptamine in the brain tissue was demonstrated. In the absence of a monoamine oxidase inhibitor, the mean +/- S.D. levels of 5-methoxytryptamine in the rat and quail whole brain were found to be 30 +/- 6 and 347 +/- 52 pg/g, respectively. The possible physiological functions of 5-methoxytryptamine as a neuromodulator and/or neurotransmitter have to be considered. PMID:8844409

Tsang, C W; Chan, C L; Li, P; Pang, S F

1996-07-12

52

Determination of free and glucuronide conjugated 20-hydroxyarachidonic acid (20-HETE) in urine by gas chromatography/negative ion chemical ionization mass spectrometry.  

PubMed

20-Hydroxy-arachidonic acid (20-HETE) was determined in urine by an isotope dilution assay using gas chromatography/mass spectrometry (GC/MS). After addition of 18O2-internal standard, 20-HETE was extracted from urine with hexane either directly or after treatment with glucuronidase. 20-HETE was derivatized to the pentafluorobenzylester and the sample was applied to thin layer chromatography with iso-octane/iso-propanol 9:1 (v/v) as the developing solvent. The corresponding zone was extracted and 20-HETE was hydrogenated. After derivatization to the trimethylsilylether, 20-HETE was determined by GC/MS using the [M-pentafluorobenzyl]- -ion in the negative ion chemical ionization mode. Excretion rates of free and glucuronide conjugated 20-HETE was determined in healthy children and in children with hyperprostaglandin-E-syndrome/antenatal Bartter syndrome (HPS/aBS) with or without indomethacin treatment. Compared to the controls, the HPS/aBS children showed higher excretion rates of 20-HETE, which were suppressed to normal values under indomethacin medication. Free and glucuronide conjugated 20-HETE do not correlate with PGE2 excluding any participation in HPS/aBS. PMID:10841040

Watzer, B; Reinalter, S; Seyberth, H W; Schweer, H

2000-03-01

53

An Examination of Pentafluorobenzoyl Derivatization Strategies for the Analysis of Fatty Alcohols using Gas Chromatography/Electron Capture Negative Ion Chemical Ionization-Mass Spectrometry  

PubMed Central

Gas chromatography/electron capture negative ion chemical ionization-mass spectrometry (GC/ECNICI-MS) combined with pentafluorobenzoyl derivatization (PFBoyl) is frequently used for the sensitive detection of fatty alcohols (FOH). However, this derivatization technique suffers from a lack of established reaction protocols, time-consuming reactions, and the presence of reagent artifacts or unwanted derivatization byproducts which can hinder analyte detection. Here, strategies are presented to reduce the problems associated with PFBoyl-derivatization, including 1) the optimization of reaction conditions (derivatization time and temperature) for a variety of PFBoyl-derivatized FOH, 2) an investigation of microwave-accelerated derivatization (MAD) as a rapid alternative heating mechanism for the PFBoyl-derivatization of FOH, and 3) an analysis of an alternative strategy employing a solvent extraction procedure post-derivatization to reduce the detrimental effects commonly associated with PFBoyl derivatization reagents. The optimal reaction conditions for the PFBoyl-derivatization of FOH was determined to be 60 °C for 45 min. The investigation in MAD demonstrated the potential of obtaining comparable PFBoyl-derivatizations to those obtained using traditional heating methods, albeit in a reaction time of 3 min. An examination of several solvents for post-derivatization extraction revealed improved relative response factors in comparison to those obtained without solvent extraction. The best solvents for the PFBoyl-FOH extraction, dichloromethane and tert-butyl methyl ether, were also compared to the no solvent extraction samples with standard response curves and PFBoyl-derivatized FOH in Bligh-Dyer extracted rat plasma.

Bowden, John A.; Ford, David A.

2010-01-01

54

Development and use of Negative Ion Proton Transfer Reaction Chemical Ionization Mass Spectrometry (NI-PTR-CIMS) for the Measurement of Trace Organic Acids in the Atmosphere  

NASA Astrophysics Data System (ADS)

Negative-Ion Proton-Transfer Reaction Chemical Ionization Mass Spectrometry (NI-PTR-CIMS) has been developed for real-time measurement of gas-phase organic acids in the atmosphere. The method is based on the non-dissociative proton transfer reactions of CH3COO- with most of the common organic acids. The potential to detect organic acids (monocarboxylic, dicarboxylic, inorganic, and rare acids) has been shown by a number of laboratory investigations. The sensitivity of the instrument to several organic acids has been observed to be on the order of several ion counts per pptv. Detection limits well below the ppbv level are expected for a 1-second integration time. Various instrumental features including zeroing, time response, calibration and validation of the ion chemistry have been investigated and will be discussed. Intercomparison of formic acid measurements with Proton Transfer Reaction Mass Spectrometry (PTR-MS) and Quantum Cascade Laser IR absorption (QCL) serve to validate this measurement technique. Further development of this instrument will provide a fast, sensitive, and selective measurement technique for gas-phase acids. NI-PTR-CIMS has great potential for use in atmospheric chemistry field studies.

Veres, P.; Roberts, J. M.; Warneke, C.; de Gouw, J.; Herndon, S.; Zahniser, M.

2007-12-01

55

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

SciTech Connect

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

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

2005-05-01

56

Ionization phenomena and sources of negative ions  

SciTech Connect

Negative ion source technology has rapidly advanced during the past several years as a direct consequence of the discovery of Krohn that negative ion yields can be greatly enhanced by sputtering in the presence of Group IA elements. Today, most negative ion sources use this discovery directly or the principles implied to effect negative ion formation through surface ionization. As a consequence, the more traditional direct extraction plasma and charge exchange sources are being used less frequently. However, the charge exchange generation mechanism appears to be as universal, is very competitive in terms of efficiency and has the advantage in terms of metastable ion formation. In this review, an attempt has been made to briefly describe the principal processes involved in negative ion formation and sources which are representative of a particular principle. The reader is referred to the literature for specific details concerning the operational characteristics, emittances, brightnesses, species and intensity capabilities of particular sources. 100 references.

Alton, G.D.

1983-01-01

57

Chemical protection against ionizing radiation  

NASA Astrophysics Data System (ADS)

Some of the problems related to chemical protection against ionizing radiation are discussed with emphasis on : definition, classification, degree of protection, mechanisms of action and toxicity. Results on the biological response modifyers (BRMs) and on the combination of nontoxic (i.e. low) doses of sulphydryl radioprotectors and BRMs are presented.

Maisin, J. R.

58

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

Microsoft Academic Search

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

O. Moehler; F. Arnold

1991-01-01

59

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

60

Development and validation of an analytical method for determination of 3-chloropropane-1,2-diol in rat blood and urine by gas chromatography-mass spectrometry in negative chemical ionization mode  

Microsoft Academic Search

We have developed a highly selective and sensitive method using gas chromatography-mass spectrometry with negative chemical\\u000a ionization for measuring 3-chloropropane-1,2-diol (3-MCPD) in rat blood and urine. Samples were adsorbed on silica gel, extracted\\u000a with ethyl acetate, and derivatized by chemical derivatization with heptafluorobutyric acid anhydride. For quantification,\\u000a matrix-based calibration curves and 3-MCPD-d\\u000a 5, as an isotope-labeled internal standard, were used.

Edith Berger-Preiß; Susanne Gerling; Elisabeth Apel; Alfonso Lampen; Otto Creutzenberg

2010-01-01

61

Negative surface ionization - Intense halogen-ion source  

Microsoft Academic Search

A surface negative-ionization source was created in order to produce intense negative-ion beams. The advantages of an ionizer functioning in transmission were shown, which led to the theoretical determination of ionizer-pore useful dimensions. It was thus shown that, contrary to the case with positive ions, the pore diameter necessary for a satisfactory transmission-ionization efficiency is highly dependent on the electron

J. Pelletier; C. Pomot; J. Cocagne

1979-01-01

62

Tungsten isotope ratio determinations by negative thermal ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

A precise determination of the isotopic abundances of tungsten with natural isotopic composition is presented. WO-3 ions are generated by negative thermal ionization (NTI) in a double-filament ion source. La2O3 is used as a chemical substance to reduce the electron work function of the rhenium filament material. An ionization efficiency of 1% is obtained for sample loadings of 100 ng. The isotopic abundances are measured with relative standard deviations of 0.2% for the least abundant 180W isotope and 0.02-0.004% for the other tungsten isotopes. These improved isotopic data are used to recalculate the atomic weight of tungsten as 183.8417 ± 0.0001. The new NTI technique is an ideal tool for the application of isotope dilution mass spectrometry to analyse tungsten traces and for the measurement of isotopic shifts of this element in meteorites produced by the decay of 182Hf.

Völkening, Joachim; Köppe, Manfred; Heumann, Klaus G.

1991-07-01

63

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

2008-11-11

64

Development and validation of an analytical method for determination of 3-chloropropane-1,2-diol in rat blood and urine by gas chromatography-mass spectrometry in negative chemical ionization mode.  

PubMed

We have developed a highly selective and sensitive method using gas chromatography-mass spectrometry with negative chemical ionization for measuring 3-chloropropane-1,2-diol (3-MCPD) in rat blood and urine. Samples were adsorbed on silica gel, extracted with ethyl acetate, and derivatized by chemical derivatization with heptafluorobutyric acid anhydride. For quantification, matrix-based calibration curves and 3-MCPD-d (5), as an isotope-labeled internal standard, were used. The relative recoveries of 3-MCPD were between 80 and 110% in most cases and the relative standard deviations were typically less than 10%, with some exceptions. The limit of quantification of the method was found to be about 2 ng/mL. In conclusion, a valuable, robust, and sensitive method for detection of 3-MCPD is now available for biokinetics studies. PMID:20640896

Berger-Preiss, Edith; Gerling, Susanne; Apel, Elisabeth; Lampen, Alfonso; Creutzenberg, Otto

2010-07-18

65

Ionization Phenomena and Sources of Negative Ions.  

National Technical Information Service (NTIS)

Negative ion source technology has rapidly advanced during the past several years as a direct consequence of the discovery of Krohn that negative ion yields can be greatly enhanced by sputtering in the presence of Group IA elements. Today, most negative i...

G. D. Alton

1983-01-01

66

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.

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

67

Simultaneous determination of beclomethasone, beclomethasone monopropionate and beclomethasone dipropionate in biological fluids using a particle beam interface for combining liquid chromatography with negative-ion chemical ionization mass spectrometry.  

PubMed

A new simple and sensitive assay has been developed for the simultaneous quantitative measurement of beclomethasone dipropionate and its hydrolysis products in human plasma and urine. Beclomethasone 17.21-dipropionate, beclomethasone 17-monopropionate, beclomethasone and the internal standard, dexamethasone 21-acetate, were measured by combined liquid chromatography and negative-ion chemical ionization mass spectrometry with methane as the reagent gas. A particle beam interface from Hewlett Packard was used. Under mild operating conditions, abundant and stable characteristic high-mass ions were generated in the ion source of the mass spectrometer by a resonance electron-capture mechanism. The fast extraction procedure requires 1 ml of plasma or urine, and the quantification limit of the method is 1 ng ml-1 for the three tested compounds. PMID:1860934

Girault, J; Istin, B; Malgouyat, J M; Brisson, A M; Fourtillan, J B

1991-03-01

68

Synthesis of trans-4,5-epoxy-(E)-2-decenal and its deuterated analog used for the development of a sensitive and selective quantification method based on isotope dilution assay with negative chemical ionization.  

PubMed

The volatile compound trans-4,5-epoxy-(E)-2-decenal (1) was synthesized in two steps with good overall yields. The newly developed method is based on trans-epoxidation of (E)-2-octenal with alkaline hydrogen peroxide followed by a Wittig-type chain elongation with the ylide formylmethylene triphenylphosphorane. For the synthesis of [4,5-2H2]-trans-4,5-epoxy-(E)-2-decenal (d-1), [2,3-2H2]-(E)-2-octenal was prepared by reduction of 2-octyn-1-ol with lithium aluminum deuteride and subsequent oxidation of [2,3-2H2]-(E)-2-octen-1-ol with manganese oxide. Compound d1 was used as internal standard for the quantification of 1 by isotope dilution assay. Among various mass spectrometry (MS) ionization techniques tested, negative chemical ionization with ammonia as reagent gas gave best results with respect to both sensitivity and selectivity. The detection limit was found to be at about 1 pg of the analyte introduced into the gas chromatography-MS system. PMID:10580339

Lin, J; Fay, L B; Welti, D H; Blank, I

1999-10-01

69

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

SciTech Connect

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

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

1995-12-31

70

Chemical Dosimetry of Ionizing Radiations.  

National Technical Information Service (NTIS)

This volume generalizes the theoretical and experimental material that has been accumulated during recent years in the field of chemical dosimetry. Attention is focused on the justification for the use of chemical-dosimetry methods to solve problems that ...

A. M. Kabakchi Y. I. Lavrentovich V. V. Penkovskii

1966-01-01

71

Determination of Organobromide Compounds in Water by Gas Chromatography-Negative Ion Chemical Ionisation Mass Spectrometry.  

National Technical Information Service (NTIS)

Gas chromatography-negative ion chemical ionization mass spectrometry (GC-NCIMS) was evaluated as a method for qualitative and quantitative determination of organobromine compounds in water. The negative ion mass spectra of bromine-containing trihalometha...

K. Koida Y. Kohno Y. Fukuda K. Sekigawa S. Yoshizaki

1985-01-01

72

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

73

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions  

NASA Astrophysics Data System (ADS)

A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO3), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO3 and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4 s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO3·NO3- clusters within the CIMS, and NO2-water production on inlet surfaces, and were quite minor (?1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products.

Roberts, J. M.; Veres, P.; Warneke, C.; Neuman, J. A.; Washenfelder, R. A.; Brown, S. S.; Baasandorj, M.; Burkholder, J. B.; Burling, I. R.; Johnson, T. J.; Yokelson, R. J.; de Gouw, J.

2010-07-01

74

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions  

NASA Astrophysics Data System (ADS)

A negative-ion proton transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO3), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO3 and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4 s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO3·NO3- clusters within the CIMS, and NO2-water production on inlet surfaces, and were quite minor (?1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products.

Roberts, J. M.; Veres, P.; Warneke, C.; Neuman, J. A.; Washenfelder, R. A.; Brown, S. S.; Baasandorj, M.; Burkholder, J. B.; Burling, I. R.; Johnson, T. J.; Yokelson, R. J.; de Gouw, J.

2010-01-01

75

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

SciTech Connect

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

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

2010-07-23

76

A Tubular Ionizer as an Efficient Negative Fluorine Ion Source  

NASA Astrophysics Data System (ADS)

In order to establish the optimal conditions of F- ion production by the tubular ionizer extensive studies of SF6 ionization using the mass separator were performed. The SF6, SF5, SF4, SF3 and F negative ions were observed, and the F- yields as a function of the source temperature, gas pressure and an amount of alkaline metal vapors (K, Na, Ca, Sr, Ba) were measured. The efficiency of F- production of about 40obtained for the optimal conditions. The delay time and adsorption enthalpy of fluorine on the tantalum surface has been measured for the first time.

Piotrowski, A.; Kozlowski, T.

2000-01-01

77

Automated analysis of 2-methyl-3-furanthiol and 3-mercaptohexyl acetate at ng L(-1) level by headspace solid-phase microextracion with on-fibre derivatisation and gas chromatography-negative chemical ionization mass spectrometric determination.  

PubMed

A fast and automated method for the analysis at ng L(-1) level of aroma-powerful polyfunctional thiols has been developed and applied to wine. The sample is just poured in a 20 mL vial and its vapour extracted with a poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) solid-phase microextraction fibre (65 microm thickness) previously exposed to vapours of the reactive (pentafluorobenzyl bromide) and of an alkali (tributylamine). The derivatised compounds are subsequently desorbed in the GC system and determined by negative chemical ionization mass spectrometry. The method is fully automated by using a Combi-Pal autosampler conveniently programmed. The analysis takes 50 min, which contrasts to the long and tedious methods previously proposed. The development of an optimal procedure is constrained by the aggressive character of the reagent (towards the fibre and the chromatographic column), its volatility and the quality of the blanks that can be obtained. Therefore, a critical step was fixing in the fibre a "safe" and repetitive amount of reagent. This was achieved by exposing the fibre (5 min) to the vapours of a water:acetone (9:1) solution containing 200mg L(-1) of reagent. Under these conditions, the extraction-derivatisation of analytes improves with time and temperature, and the best working conditions are dictated by a compromise between sensitivity, speed and chromatographic performance. Although analytes studied were 2-methyl-3-furanthiol, 4-mercapto-4-methyl-2-pentanone, 3-mercaptohexanol, 2-furanmethanethiol and 3-mercaptohexyl acetate, a good analytical performance could be achieved only for these two last compounds. Both of them can be repetitively (10%

Mateo-Vivaracho, Laura; Ferreira, Vicente; Cacho, Juan

2006-05-06

78

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.  

PubMed

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 30 mg of hair by aqueous incubation and purified by solid-phase extraction (SPE) using mixed mode extraction cartridges followed by derivation with perfluoropentanoic anhydride (PFPA). The analysis was performed in the selected reaction monitoring (SRM) mode using the transitions m/z 347-->163 (for the quantification) and m/z 347-->119 (for the identification) for EtG, and m/z 352-->163 for EtG-d(5) used as internal standard. For validation, we prepared quality controls (QC) using hair samples taken post mortem from 2 subjects with a known history of alcoholism. These samples were confirmed by a proficiency test with 7 participating laboratories. The assay linearity of EtG was confirmed over the range from 8.4 to 259.4 pg/mg hair, with a coefficient of determination (r(2)) above 0.999. The limit of detection (LOD) was estimated with 3.0 pg/mg. The lower limit of quantification (LLOQ) of the method was fixed at 8.4 pg/mg. Repeatability and intermediate precision (relative standard deviation, RSD%), tested at 4 QC levels, were less than 13.2%. The analytical method was applied to several hair samples obtained from autopsy cases with a history of alcoholism and/or lesions caused by alcohol. EtG concentrations in hair ranged from 60 to 820 pg/mg hair. PMID:19109074

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

2008-12-06

79

Characteristics of low-temperature plasma ionization for ambient mass spectrometry compared to electrospray ionization and atmospheric pressure chemical ionization.  

PubMed

Ambient desorption/ionization mass spectrometry (ADI-MS) is an attractive method for direct analysis with applications in homeland security, forensics, and human health. For example, low-temperature plasma probe (LTP) ionization was successfully used to detect, e.g., explosives, drugs, and pesticides directly on the target. Despite the fact that the field is gaining significant attention, few attempts have been made to classify ambient ionization techniques based on their ionization characteristics and performance compared to conventional ionization sources used in mass spectrometry. In the present study, relative ionization efficiencies (RIEs) for a large group of compound families were determined with LTP-Orbitrap-MS and compared to those obtained with electrospray ionization mass spectrometry (ESI-MS) and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). RIEs were normalized against one reference compound used across all methods to ensure comparability of the results. Typically, LTP analyte ionization through protonation/deprotonation (e.g., 4-acetamidophenol) was observed; in some cases (e.g., acenaphthene) radicals were formed. Amines, amides, and aldehydes were ionized successfully with LTP. A benefit of LTP over conventional methods is the possibility to successfully ionize PAHs and imides. Here, the studied model compounds could be detected by neither APCI nor ESI. LTP is a relatively soft ionization method because little fragmentation of model compounds was observed. It is considered to be an attractive method for the ionization of low molecular weight compounds over a relatively wide polarity range. PMID:23134531

Albert, Anastasia; Engelhard, Carsten

2012-11-26

80

Probing chemical dynamics with negative ions  

SciTech Connect

Experiments are reviewed in which key problems in chemical dynamics are probed by experiments based on photodetachment and/or photoexcitation of negative ions. Examples include transition state spectroscopy of biomolecular reactions, spectroscopy of open shell van der Waals complexes, photodissociation of free radicals, and time-resolved dynamics in clusters. The experimental methods used in these investigations are described along with representative systems that have been studied.

Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2006-10-07

81

Charge state reduction of oligonucleotide negative ions from electrospray ionization  

SciTech Connect

We have investigated the feasibility of simplifying the electrospray ionization (ESI) mass spectra for mixture analyses through charge state reduction. Two methods for charge state reduction of gas phase oligonucleotide negative ions were evaluated: (1) the addition of acids to the oligonucleotide solution and (2) the formation of diamine adducts followed by dissociation in the interface region. In the first method, the efficiency of charge state reduction depends on the pK[sub a], the concentration, and the nature of the acids. Acetic and formic acids were found to be better reagents than HCl, CF[sub 3]CO[sub 2]H, and H[sub 3]PO[sub 4]. The second method has the advantage that the stability of oligonucleotides is not affected but requires the optimization of the interface dissociation conditions and the amounts of diamine added to the oligonucleotide solution. Both methods show promise for charge state reduction, and results are presented for two oligonucleotides: d(pT)[sub 12] and d(AGCT). Substantial reduction in spectral complexity upon charge state reduction was also observed for a four-component mixture of oligonucleotides. 54 refs., 8 figs.

Cheng, X.; Gale, D.C.; Udseth, H.R.; Smith, R.D. (Pacific Northwest Lab., Richland, WA (United States))

1995-02-01

82

Ionization equilibrium and equation of state of partially ionized hydrogen plasmas: Pseudopotential approach in chemical picture  

SciTech Connect

Starting from the Bogolyubov hierarchy for the equilibrium distribution functions, a novel approach to the chemical model of partially ionized plasmas is proposed. Unlike the ordinary chemical picture it allows one to determine, in a self-consistent manner, both the ionization equilibrium and correlation functions as well. It is shown that the charged and neutral components of the plasma are closely interrelated and, as a consequence, the short-range order formation turns possible. The equation of state of partially ionized hydrogen plasmas is studied and detailed comparison with an exact quantum-mechanical expansion is made. The approach developed is quite analogous to the Debye-Hueckel theory of weakly coupled fully ionized plasmas and includes it as a limiting case.

Arkhipov, Yu.V.; Baimbetov, F.B.; Davletov, A.E. [Department of Physics, Kazakh National University, Tole Bi 96, 480012 Almaty (Kazakhstan)

2005-08-15

83

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

84

Analysis of the residues of 20 organochlorine pesticides in Herba epimedii, a Chinese herbal medicine, by solid-phase extraction with gas chromatography/negative chemical ionization-mass spectrometry.  

PubMed

A multiresidue analytical method has been developed to simultaneously determine the residues of 20 organochlorine pesticides in Herba epimedii, a traditional Chinese medicine. The 20 pesticides are included in the list of regulated substances by the Food and Environmental Hygiene Department in Hong Kong. The method consists of solid-phase extraction for cleanup of samples and GC coupled on-line with negative chemical ion-MS to analyze the target pesticides. The chromatographic separation of the compounds was carried out on a DB-1701 column by using an optimal temperature program, and the quantitative analysis was conducted by selected ion monitoring. The LOD and LOQ values fell in the range of 0.0555-5.8821 and 0.1241-17.9333 ng/g, respectively. The average recoveries were between 75.4 and 90.7% (n=5) for the 20 organochlorine pesticides. The developed method proved to be reliable and accurate, and permits rapid determination of the 20 organochlorine pesticides in one run. PMID:20334191

Guo, Qing; Deng, Ming; Yu, Boyang; Tan, Li

85

Impact Ionization, Bulk Negative Differential Conductivity and Other Nonequilibrium Carrier Phenomena in InSb.  

National Technical Information Service (NTIS)

The hot electron effect, injection, impact ionization and bulk negative differential conductivity are nonequilibrium carrier phenomena that some semiconductors exhibit. In particular, all four phenomena affect conduction in InSb in a strongly interrelated...

C. L. Dick B. Ancker-Johnson

1970-01-01

86

Electron-Capture Negative Ionization Calibrants for Magnetic Sector Mass Spectrometers.  

National Technical Information Service (NTIS)

Fomblin poly(perfluoropropylene oxide), PFK (perfluorokerosene) and FC-43 (perfluorotributylamine) are investigated as mass calibrants in electron-capture negative ionization mass spectrometry on a magnetic sector hybrid mass spectrometer. This work provi...

G. M. Brilis W. C. Brumley

1990-01-01

87

UPTAKE OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS  

EPA Science Inventory

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

88

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

Microsoft Academic Search

We constructed a new chemical ionization time-of-flight mass spectrometer (CI-TOFMS) that measures atmospheric trace gases in real time with high sensitivity. We apply the technique to the measurement of formic acid via negative-ion proton transfer, using acetate as the reagent ion. A novel high pressure interface, incorporating two RF-only quadrupoles is used to efficiently focus ions through four stages of

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

2011-01-01

89

Self-consistent chemical model of partially ionized plasmas  

SciTech Connect

A simple renormalization theory of plasma particle interactions is proposed. It primarily stems from generic properties of equilibrium distribution functions and allows one to obtain the so-called generalized Poisson-Boltzmann equation for an effective interaction potential of two chosen particles in the presence of a third one. The same equation is then strictly derived from the Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy for equilibrium distribution functions in the pair correlation approximation. This enables one to construct a self-consistent chemical model of partially ionized plasmas, correctly accounting for the close interrelation of charged and neutral components thereof. Minimization of the system free energy provides ionization equilibrium and, thus, permits one to study the plasma composition in a wide range of its parameters. Unlike standard chemical models, the proposed one allows one to study the system correlation functions and thereby to obtain an equation of state which agrees well with exact results of quantum-mechanical activity expansions. It is shown that the plasma and neutral components are strongly interrelated, which results in the short-range order formation in the corresponding subsystem. The mathematical form of the results obtained enables one to both firmly establish this fact and to determine a characteristic length of the structure formation. Since the cornerstone of the proposed self-consistent chemical model of partially ionized plasmas is an effective pairwise interaction potential, it immediately provides quite an efficient calculation scheme not only for thermodynamical functions but for transport coefficients as well.

Arkhipov, Yu. V.; Baimbetov, F. B.; Davletov, A. E. [Department of Physics, Kazakh National University, Tole Bi 96, Almaty 050012 (Kazakhstan)

2011-01-15

90

Self-consistent chemical model of partially ionized plasmas.  

PubMed

A simple renormalization theory of plasma particle interactions is proposed. It primarily stems from generic properties of equilibrium distribution functions and allows one to obtain the so-called generalized Poisson-Boltzmann equation for an effective interaction potential of two chosen particles in the presence of a third one. The same equation is then strictly derived from the Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy for equilibrium distribution functions in the pair correlation approximation. This enables one to construct a self-consistent chemical model of partially ionized plasmas, correctly accounting for the close interrelation of charged and neutral components thereof. Minimization of the system free energy provides ionization equilibrium and, thus, permits one to study the plasma composition in a wide range of its parameters. Unlike standard chemical models, the proposed one allows one to study the system correlation functions and thereby to obtain an equation of state which agrees well with exact results of quantum-mechanical activity expansions. It is shown that the plasma and neutral components are strongly interrelated, which results in the short-range order formation in the corresponding subsystem. The mathematical form of the results obtained enables one to both firmly establish this fact and to determine a characteristic length of the structure formation. Since the cornerstone of the proposed self-consistent chemical model of partially ionized plasmas is an effective pairwise interaction potential, it immediately provides quite an efficient calculation scheme not only for thermodynamical functions but for transport coefficients as well. PMID:21405782

Arkhipov, Yu V; Baimbetov, F B; Davletov, A E

2011-01-21

91

ECC and direct ionization in positron negative hydrogen ion collision  

NASA Astrophysics Data System (ADS)

The dynamics of the electron capture to continuum (ECC) phenomenon is studied for the first time for the positron-negative hydrogen ion (H-) system where an electron of the H- ion is captured to a low continuum of the incident positron (e+), leaving behind a residual neutral hydrogen atom. The calculations are performed in the framework of the Coulomb distorted eikonal approximation (CDEA) as well as with two other simplified models. The triple differential cross sections (TDCS) for the ejected electron distribution as well as the double differential cross sections (DDCS) with respect to energy and emission angle of the ejected electron are studied. The TDCS is found to be highly peaked at the forward ejection angle when the ejected electron and the scattered positron share equally or almost equally (Ee ap Ep) the available energy in the exit channel for both the post form and the prior form of interactions, indicating the signature of ECC. An asymmetric ridge-like structure is also obtained in the present DDCS for the ejected energy distribution. The DDCS with respect to the emission angle of the ejected electron shows some interestingly different behaviour from that noted for a neutral target, e.g., the occurrence of a distinct sharp peak at 45° for nearly equal energy sharing between the e and the e+, which could probably be attributed to the presence of one loosely bound target electron in H-. For positron impact, due to its small mass, the ECC cusp has a spread in the velocity space around \\vec{v_e}= \\vec{v_p} , unlike the heavy-ion impact. Some novel features are also noted in the TDCS of the ionic target (H-) for both symmetric and asymmetric kinematics.

Ghosh, D.; Sinha, C.

2005-01-01

92

New quantification procedure for the analysis of chlorinated paraffins using electron capture negative ionization mass spectrometry  

Microsoft Academic Search

An improved quantification procedure for the analysis of chlorinated paraffins (CPs) is presented based on electron capture negative ionization mass spectrometry. It compensates differences in response factors between reference CP mixtures and the CP pattern present in environmental samples. The use of a CP standard with a matching degree of chlorination is no longer necessary. It could be shown that

Margot Reth; Zdenek Zencak; Michael Oehme

2005-01-01

93

Osmium isotope ratio measurements by negative thermal ionization mass spectrometry (NTI-MS)  

Microsoft Academic Search

A negative thermal ionization technique using a Faraday cup as detector is presented, which allows precise isotope ratio measurements of osmium. For the major isotopes the relative standard deviation is in the range of 0.004% to 0.07%. Sample amounts down to 1 ng were loaded as hexachloroosmic acid. From the results it is concluded that also sample amounts in the

Thomas Walczyk; Erhard H. Hebeda; Klaus G. Heumann

1991-01-01

94

Application of computer pattern recognition to metal ion chemical ionization mass spectrometry data  

Microsoft Academic Search

The first application of computer pattern recognition to the analysis of low pressure transition metal ion chemical ionization (MICI) data is described. The data have been collected using a conventional ion cyclotron resonance (ICR) mass spectrometer and a Fourier transform mass spectrometer (FTMS) equipped with laser ionization sources. Chemical ionization data for organic compounds of several classes with various transition

1986-01-01

95

Chemical Ionization Mass Spectrometric Measurements of Atmospheric Trace Gases  

NASA Astrophysics Data System (ADS)

Chemical Ionization Mass Spectrometry (CIMS) is a versatile, fast and sensitive method for the detection of atmospheric trace gases, which play key roles in atmospheric chemistry and climate. A combination of different types of mass spectrometers, ion sources and inlet configurations are deployed by IPA. Sophisticated calibration techniques and in-flight calibration systems are developed to ensure high data quality. The CIMS instruments are employed preferably on research aircraft; in addition, observations are performed on ships, ground based sites and in laboratory scenarios including atmospheric chambers.

Aufmhoff, Heinfried; Schäuble, Dominik; Roiger, Anke; Arnold, Frank; Jurkat, Tina; Voigt, Christiane; Schlager, Hans

96

Evidence of Negative-Index Refraction in Nonlinear Chemical Waves  

Microsoft Academic Search

The negative index of refraction of nonlinear chemical waves has become a recent focus in nonlinear dynamics researches. Theoretical analysis and computer simulations have predicted that the negative index of refraction can occur on the interface between antiwaves and normal waves in a reaction-diffusion (RD) system. However, no experimental evidence has been found so far. In this Letter, we report

Xujin Yuan; Hongli Wang; Qi Ouyang

2011-01-01

97

Collection of airborne fluorinated organics and analysis by gas chromatography/chemical ionization mass spectrometry.  

PubMed

The ubiquitous detection of perfluorooctane sulfonate (PFOS) in humans and animals has produced a need for sensitive and compound-specific analytical methods to determine the environmental distribution of fluorinated organic contaminants. A suite of potential PFOS precursors (sulfonamides) and fluorotelomer alcohols (FTOHs) were separated by gas chromatography and detected by chemical ionization mass spectrometry (GC/CI-MS). Full-scan spectra were collected in both positive and negative chemical ionization (PCI and NCI, respectively) mode to determine retention time windows and fragmentation patterns. In selected ion monitoring (SIM) mode, instrumental detection limits ranged from 0.2 to 20 pg for individual analytes, depending on ionization mode. PCI mode was preferred for routine analysis because of the simple mass spectra produced, typified by the presence of a major molecular ion [M + H]+. High-volume air samplers collected gaseous and particle-bound fluoroorganics on composite media consisting of XAD-2, polyurethane foam (PUF), and quartz-fiber filters. The combined collection efficiency for individual analytes was 87 to 136% in breakthrough experiments. Application of the method to the analysis of ambient air from urban and rural sites confirmed the presence of six novel fluorinated atmospheric contaminants at picogram per meter3 concentrations. Low concentrations of fluoroorganics were consistently detected in blanks (<4 pg m(-3)); however, this did not prevent confirmation or quantification of environmental concentrations. PMID:11842814

Martin, Jonathan W; Muir, Derek C G; Moody, Cheryl A; Ellis, David A; Kwan, Wai Chi; Solomon, Keith R; Mabury, Scott A

2002-02-01

98

The chemical composition of ionized gas in galaxies  

NASA Astrophysics Data System (ADS)

Active star formation in galaxies takes place in HII regions harbouring young massive stars within an extended ionized gaseous component. Their relative structural simplicity andcharacteristic emission line spectrum make them ideal laboratories to study the physical properties and chemical composition of gas and stars in galaxies. Chemical abundancescan be derived for Galactic and relatively nearby extragalactic HII regions, as well as for distant galaxies, applying different techniques. In this talk an overview of the derivation of chemical abundances for HII regions in galaxies is presented, with an emphasis on the different domains of spatial resolution covered by the data, from spatially resolved integral field spectra of HII regions in the Milky Way and nearby galaxies to integrated spectra of more distant galaxies.With the upcome of the new integral field spectrographs a wide coverage at good spatial sampling of galaxies and HII complexes is now possible. This new 2D spectroscopy provides us more realistic information and useful constrains to study the chemical enrichment process of the interstellar medium and some of the fundamental relations governing galaxy evolution.

Vilchez, J. M.

2011-11-01

99

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

Microsoft Academic Search

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

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

2009-01-01

100

Negative ion mode electrospray ionization mass spectrometry study of ammonium-counter ion clusters  

Microsoft Academic Search

Electrospray ionization mass spectrometry (ESI-MS) was used to examine clusters of protonated amine salt solutions with chloride\\u000a counter ions in the negative ion mode. These ions have the general formula [(RNH3)xClx+1]?. Primary amines generate a wide cluster distribution with clusters up to 14 mer for methylamine hydrochloride clusters. Secondary\\u000a and quaternary amines only generate the monomer ion under identical conditions.

N. B. Lentz; R. S. Houk

2007-01-01

101

Iridium isotope ratio measurements by negative thermal ionization mass spectrometry and atomic weight of iridium  

NASA Astrophysics Data System (ADS)

A technique of negative thermal ionization mass spectrometry (NTI-MS) for the precise iridium isotope ratio determination is presented. IrO-2 and IrO-3 ions are formed in a double-filament (Pt) ion source using (NH4)2IrCl6 as a sample compound. The IrO-2 ion current always exceeds the IrO-3 current by a factor of about 50-300 depending on the filament temperature and the oxygen gas introduced into the ion source. IrO-3 ion currents of more than 10-11 A can be obtained at the detector side from 100 ng iridium samples. The relative standard deviation of the 191Ir/193 ratio determination is 0.06%, which is much better than the data quoted in past literature. From such data the atomic weight of iridium could be calculated to be 192.21661 ± 0.00029. This value is a great improvement when compared with the iridium atomic weight of 192.22 ± 0.03 recommended by IUPAC. Additionally, an NTI-MS technique has been developed which allows the simultaneous measurement of iridium and osmium isotope ratio from osmiridium samples without any chemical separation. The iridium isotope ratios of three osmiridium samples agree well with the ratios determined from the hexachloroiridate compound. The direct 187Os/186OS determination from osmiridium samples opens the possibility of studying the evolution of osmium in the Earth's mantle due to the radioactive decay of 187Re into 187Os.

Walczyk, Thomas; Heumann, Klaus G.

1993-02-01

102

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

103

Isolation and Chemical Characterization of Lipid A from Gram-negative Bacteria.  

PubMed

Lipopolysaccharide (LPS) is the major cell surface molecule of gram-negative bacteria, deposited on the outer leaflet of the outer membrane bilayer. LPS can be subdivided into three domains: the distal O-polysaccharide, a core oligosaccharide, and the lipid A domain consisting of a lipid A molecular species and 3-deoxy-D-manno-oct-2-ulosonic acid residues (Kdo). The lipid A domain is the only component essential for bacterial cell survival. Following its synthesis, lipid A is chemically modified in response to environmental stresses such as pH or temperature, to promote resistance to antibiotic compounds, and to evade recognition by mediators of the host innate immune response. The following protocol details the small- and large-scale isolation of lipid A from gram-negative bacteria. Isolated material is then chemically characterized by thin layer chromatography (TLC) or mass-spectrometry (MS). In addition to matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) MS, we also describe tandem MS protocols for analyzing lipid A molecular species using electrospray ionization (ESI) coupled to collision induced dissociation (CID) and newly employed ultraviolet photodissociation (UVPD) methods. Our MS protocols allow for unequivocal determination of chemical structure, paramount to characterization of lipid A molecules that contain unique or novel chemical modifications. We also describe the radioisotopic labeling, and subsequent isolation, of lipid A from bacterial cells for analysis by TLC. Relative to MS-based protocols, TLC provides a more economical and rapid characterization method, but cannot be used to unambiguously assign lipid A chemical structures without the use of standards of known chemical structure. Over the last two decades isolation and characterization of lipid A has led to numerous exciting discoveries that have improved our understanding of the physiology of gram-negative bacteria, mechanisms of antibiotic resistance, the human innate immune response, and have provided many new targets in the development of antibacterial compounds. PMID:24084191

Henderson, Jeremy C; O'Brien, John P; Brodbelt, Jennifer S; Trent, M Stephen

2013-09-16

104

Ion chemistry of VX surrogates and ion energetics properties of VX: new suggestions for VX chemical ionization mass spectrometry detection.  

PubMed

Room temperature rate constants and product ion branching ratios have been measured for the reactions of numerous positive and negative ions with VX chemical warfare agent surrogates representing the amine (triethylamine) and organophosphonate (diethyl methythiomethylphosphonate (DEMTMP)) portions of VX. The measurements have been supplemented by theoretical calculations of the proton affinity, fluoride affinity, and ionization potential of VX and the simulants. The results show that many proton transfer reactions are rapid and that the proton affinity of VX is near the top of the scale. Many proton transfer agents should detect VX selectively and sensitively in chemical ionization mass spectrometers. Charge transfer with NO(+) should also be sensitive and selective since the ionization potential of VX is small. The surrogate studies confirm these trends. Limits of detection for commercial and research grade CIMS instruments are estimated at 80 pptv and 5 ppqv, respectively. PMID:20384284

Midey, Anthony J; Miller, Thomas M; Viggiano, A A; Bera, Narayan C; Maeda, Satoshi; Morokuma, Keiji

2010-05-01

105

Quantification of hydroxyacetone and glycolaldehyde using chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Chemical ionization mass spectrometry (CIMS) enables online, fast, in situ detection and quantification of hydroxyacetone and glycolaldehyde. Two different CIMS approaches are demonstrated employing the strengths of single quadrupole mass spectrometry and triple quadrupole (tandem) mass spectrometry. Both methods are capable of the measurement of hydroxyacetone, an analyte with minimal isobaric interferences. Tandem mass spectrometry provides direct separation of the isobaric compounds glycolaldehyde and acetic acid using distinct, collision-induced dissociation daughter ions. Measurement of hydroxyacetone and glycolaldehyde by these methods was demonstrated during the ARCTAS-CARB 2008 campaign and the BEARPEX 2009 campaign. Enhancement ratios of these compounds in ambient biomass burning plumes are reported for the ARCTAS-CARB campaign. BEARPEX observations are compared to simple photochemical box model predictions of biogenic volatile organic compound oxidation at the site.

Spencer, K. M.; Beaver, M. R.; St. Clair, J. M.; Crounse, J. D.; Paulot, F.; Wennberg, P. O.

2011-08-01

106

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

SciTech Connect

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

Zaim, H.

2001-04-16

107

Separation and characterization of phenolic compounds in argan fruit pulp using liquid chromatography–negative electrospray ionization tandem mass spectroscopy  

Microsoft Academic Search

Liquid chromatography (LC) coupled to negative electrospray ionization (ESI) tandem mass spectrometry (MS\\/MS) was used for the sensitive identification of phenolic compounds in argan fruit pulp. Sixteen compounds were identified, mainly flavonoid glycosides and flavonoid aglycons.

Zoubida Charrouf; Miloudi Hilali; Olga Jauregui; Mohamed Soufiaoui; Dominique Guillaume

2007-01-01

108

Determination of patulin in apple juice by high-performance liquid chromatography–atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

An HPLC–MS–MS method with selected reaction monitoring (SRM) for the determination of patulin in apple juice samples is described. Mass spectrometric detection was accomplished following atmospheric pressure chemical ionization (APCI) in both positive and negative ion modes. Collision induced dissociation (CID) of the protonated molecular ion led initially to the loss of H2O (fragment m\\/z 137). At higher energies CO

V Sewram; J. J Nair; T. W Nieuwoudt; N. L Leggott; G. S Shephard

2000-01-01

109

Chemical aspects of the extractive methods of ambient ionization mass spectrometry.  

PubMed

Ambient ionization techniques allow complex chemical samples to be analyzed in their native state with minimal sample preparation. This brings the obvious advantages of simplicity, speed, and versatility to mass spectrometry: Desorption electrospray ionization (DESI), for example, is used in chemical imaging for tumor margin diagnosis. This review on the extractive methods of ambient ionization focuses on chemical aspects, mechanistic considerations, and the accelerated chemical reactions occurring in charged liquid droplets generated in the spray process. DESI uses high-velocity solvent droplets to extract analytes from surfaces. Nano-DESI employs liquid microjunctions for analyte dissolution, whereas paper-spray ionization uses DC potentials applied to wet porous material such as paper or biological tissue to field emit charged analyte-containing solvent droplets. These methods also operate in a reactive mode in which added reagents allow derivatization during ionization. The accelerated reaction rates seen in charged microdroplets are useful in small-scale rapid chemical synthesis. PMID:23331308

Badu-Tawiah, Abraham K; Eberlin, Livia S; Ouyang, Zheng; Cooks, R Graham

2013-01-16

110

Liquid Chromatography Electrospray Ionization Mass Spectrometric (LC- ESI-MS) and Desorption Electrospray Ionization Mass Spectrometric (DESI-MS) Identification of Chemical Warfare Agents in Consumer Products.  

National Technical Information Service (NTIS)

Terrorist use of chemical warfare agents could involve contamination of consumer products with chemical warfare agents or other toxic chemicals. Liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) and desorption electrospray ioniza...

C. L. Chenier P. A. D'Agostino

2007-01-01

111

Comparison of electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization for determining estrogenic chemicals in water by liquid chromatography tandem mass spectrometry with chemical derivatizations.  

PubMed

This study compared the sensitivities and matrix effects of four ionization modes and four reversed-phase liquid chromatographic (LC) systems on analyzing estrone (E1), 17beta-estradiol (E2), estriol (E3), 17alpha-ethinylestradiol (EE2), 4-nonylphenol (NP), 4-tert-octylphenol (OP), bisphenol A (BPA) and their derivatives of dansyl chloride or pentafluorobenzyl bromide (PFBBr) in water matrixes using a triple-quadrupole mass spectrometer with selected reaction monitoring (SRM). The four probes were electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI) and APCI/APPI; the four LC systems were ultra-performance liquid chromatography (UPLC) with or without post-column split, a mixed-mode column and two-dimensional LC (2D-LC). Dansylated compounds with ESI at UPLC condition had the most intense signals and less matrix effects of the various combinations of ionization and LC systems. The on-column limits of detection (LODs) of dansylated estrogens by SRM were 0.05-0.20 pg, and the LODs in sewage treatment plant effluent and in river water were 0.23-0.52 and 0.56-0.91 ng/L, respectively. The LODs using selected ion monitoring (SIM) reached low ng/L levels in real samples and measured concentrations were comparable with those of SRM. PMID:19118834

Lien, Guang-Wen; Chen, Chia-Yang; Wang, Gen-Shuh

2008-12-24

112

Rapid quantitation of plasma 2?-deoxyuridine by high-performance liquid chromatography\\/atmospheric pressure chemical ionization mass spectrometry and its application to pharmacodynamic studies in cancer patients  

Microsoft Academic Search

A novel method employing high-performance liquid chromatograph–mass spectrometry (LC–MS) has been developed and validated for the quantitation of plasma 2?-deoxyuridine (UdR). It involves a plasma clean-up step with strong anion-exchange solid-phase extraction (SAX-SPE) followed by HPLC separation and atmospheric pressure chemical ionization mass spectrometry detection (APCI–MS) in a selected-ion monitoring (SIM) mode. The ionization conditions were optimised in negative ion

Kong M. Li; Laurent P. Rivory; Stephen J. Clarke

2005-01-01

113

Evidence of negative-index refraction in nonlinear chemical waves.  

PubMed

The negative index of refraction of nonlinear chemical waves has become a recent focus in nonlinear dynamics researches. Theoretical analysis and computer simulations have predicted that the negative index of refraction can occur on the interface between antiwaves and normal waves in a reaction-diffusion (RD) system. However, no experimental evidence has been found so far. In this Letter, we report our experimental design in searching for such a phenomenon in a chlorite-iodide-malonic acid (CIMA) reaction. Our experimental results demonstrate that competition between waves and antiwaves at their interface determines the fate of the wave interaction. The negative index of refraction was only observed when the oscillation frequency of a normal wave is significantly smaller than that of the antiwave. All experimental results were supported by simulations using the Lengyel-Epstein RD model which describes the CIMA reaction-diffusion system. PMID:21635131

Yuan, Xujin; Wang, Hongli; Ouyang, Qi

2011-05-06

114

Investigation on the role of pneumatic aspects in electrospray, desorption electrospray surface ionization and surface activated chemical ionization.  

PubMed

This review reports the results of some studies carried out by us on the role of pneumatic aspects in electrospray and desorption electrospray surface ionization, with the aim to propose some relevant aspects of the mechanisms involved in these ionization methods. Electrospray ion sources, with the exception of the nano- electrospray source, operate with the concurrent action of a strong electrical field and a supplementary coaxial gas flow. The electrical field is responsible for electrospraying of the analyte solution but the use of a coaxial gas flow leads to a significant increase of the analyte signal and allows the use of higher solution flows. However, by employing capillary voltages much lower than those necessary to activate the electrospray phenomenon, analyte ions are still observed and this indicates that different mechanisms must be operative for ion production. Under these conditions, ion generation could take place from the neutral pneumatically sprayed droplet by field-induced droplet ionization. Also in the case of desorption electrospray ionization (DESI), and without any voltage on the spraying capillary as well as on the surface of interest, ions of analytes present on the surface become detectable and this shows that desorption/ionization of analytes occurs by neutral droplets impinging the surface. Consequently, the pneumatic effect of the impinging droplets plays a relevant role, and for these reasons the method has been called pneumatic assisted desorption (PAD). Some analogies existing between PAD and surface activated chemical ionization (SACI), based on the insertion of a metallic surface inside an atmospheric pressure chemical ionization source operating without corona discharge, are discussed. PMID:22641720

Seraglia, Roberta; Molin, Laura; Isak, Ilena; Traldi, Pietro

2012-01-01

115

Determination of double bond position in conjugated dienes by chemical ionization mass spectrometry with isobutane  

Microsoft Academic Search

The chemical ionization (CI) mass spectra of a series of functionalized conjugated dienes, including aldehydes, alcohols, formates, acetates, and hydrocarbons were investigated to determine whether fragmentations occur that are characteristic of the position of the conjugated system within the hydrocarbon chain. CI with isobutane as ionizing gas produces structure-specific fragment ions with m\\/z ratios that can be used to locate

Robert E. Doolittle; J. H. Tumlinson; A. Proveaux

1985-01-01

116

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

117

Positive and negative analyte ion yield in matrix-assisted laser desorption/ionization revisited  

NASA Astrophysics Data System (ADS)

The most commonly accepted model for the formation of analyte ions in MALDI-MS assumes a primary ionization of the matrix e.g., by photoionization, leading among others to stable protonated and deprotonated matrix ions, respectively. Peptide and protein ions are then formed by secondary proton transfer reactions in the expanding plume. This model had been checked experimentally by comparing the yield of positive to negative ions of three peptides (Bradykinin, Angiotensin I and Fibrinopeptide A) and six matrices ([alpha]-cyano-4-hydroxycinnamicacid (CHCA), 2,5-dihydroxybenzoicacid (DHB), 6-aza-2-thiothymine (ATT), 4-nitroaniline (4-NA), 2-amino-5-nitro-4-picoline (ANP), 5-aminoquinolione (5-AQ)), differing in gas-phase basicity by about 100 kJ/mole [M. Dashtiev, E. Wäfler, U. Röhling, M. Gorshkov, F. Hillenkamp, R. Zenobi, Int. J. Mass Spetrom. 268 (2007) 122]. The data have been revisited for a more general and in-depth analysis. Model predictions are presented for a wide range of experimental parameters, in particular for ranges of the gas-phase basicity and acidity of analyte and matrix and for different molar ratios of analyte to matrix as well as the yield of primary matrix ions. It is shown that the observed ion yields cannot be explained by any single and consistent set of parameters. It is concluded that the existing simple model needs be modified to fully explain the experimental findings. Such modifications should primarily address the formation of negative matrix and analyte ions.

Hillenkamp, F.; Wäfler, E.; Jecklin, M. C.; Zenobi, R.

2009-08-01

118

Energy as Money, Chemical Bonding as Business, and Negative ?H and ?G as Investment  

NASA Astrophysics Data System (ADS)

A simple analogy is suggested illustrating the thermodynamic sign convention and the significance of the negative sign of ?H and ?G on spontaneity for general or introductory chemistry students. Enthalpy or energy is associated with money, and atoms or molecules are referred to as people. The suggested metaphor for ?H is net profit or investment into the surroundings; positive ?S is viewed as internal investment into the system. Hence, ?G is similar to gross profit in business; its dependence on temperature is illustrated by the reversal of the market trends for high-tech companies in 2000. The analogy is further expanded to illustrate the significance of ionic lattice enthalpy, the positive sign of atomic ionization energies, and chemical bond enthalpies.

Kozliak, Evguenii I.

2002-12-01

119

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

2007-09-26

120

Non-chemically amplified negative resist for EUV lithography  

NASA Astrophysics Data System (ADS)

Non-chemically amplified (CA) negative resist for EUV lithography was studied. Photo-induced thiol/ene radical reaction was used to insolubilize the resist based on poly(4-hydroxystyrene) (PHS) derivatives. Hydroxy groups of PHS were modified with allyl, norbornen, or methacrylate moiety. Dissolution property of the modified-PHS in TMAHaq solution was studied. The degree of the modification of PHS strongly affected the solubility in TMAHaq. Resist was a mixture of modified-PHS, multifunctional thiol compound, and photo-radical generator. Photo-sensitivity of the resist was studied at 254 nm and 13.5 nm. The sensitivity was affected the concentration of thiol compound added. It was found that the present resist system was highly sensitive (5~6 mJ/cm2) to EUV exposure.

Shirai, Masamitsu; Maki, Koichi; Okamura, Haruyuki; Kanayama, Koji; Itani, Toshiro

2009-03-01

121

New quantification procedure for the analysis of chlorinated paraffins using electron capture negative ionization mass spectrometry.  

PubMed

An improved quantification procedure for the analysis of chlorinated paraffins (CPs) is presented based on electron capture negative ionization mass spectrometry. It compensates differences in response factors between reference CP mixtures and the CP pattern present in environmental samples. The use of a CP standard with a matching degree of chlorination is no longer necessary. It could be shown that the response factors of C10-, C11-, C12- and C13-CP mixtures of both 50 and 60% chlorine content were only slightly influenced by the carbon chain length. A linear correlation (R2 = 0.965) between the total response factor of a CP mixture and its chlorine content was obtained for seven short chain chlorinated paraffin mixtures (SCCP, C10-C13) with different composition and chlorine content (51-69%). Maximum single deviations were <7% for this reference set. It allowed to determine the correct total response factor of the CP composition present in a sample. The deviations were not more than 7-33% for five independent SCCP control samples compared to up to 373% for the conventional procedure. The procedure was tested by quantifying the SCCP and MCCP levels in 10 fish liver samples. The proposed method allowed to compensate the influence of the degree of chlorination of the applied reference standard on the total response factor. PMID:16038213

Reth, Margot; Zencak, Zdenek; Oehme, Michael

2005-07-22

122

Chemical Processes in Protoplanetary Disks. II. On the Importance of Photochemistry and X-Ray Ionization  

NASA Astrophysics Data System (ADS)

We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization; here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find that photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2, and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+, indicating that it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine that there is a probable "dead zone" where accretion is suppressed, present in a layer, Z/R <~ 0.1-0.2, in the disk midplane, within R ? 200 AU.

Walsh, Catherine; Nomura, Hideko; Millar, T. J.; Aikawa, Yuri

2012-03-01

123

Power laws and self-similar behaviour in negative ionization fronts  

Microsoft Academic Search

We study anode-directed ionization fronts in curved geometries. An electric shielding factor determines the behaviour of the electric field and the charged particle densities. From a minimal streamer model, a Burgers type equation which governs the dynamics of the electric shielding factor is obtained when electron diffusion is neglected. A Lagrangian formulation is then derived to analyse the ionization fronts.

Manuel Arrayás; Marco A. Fontelos; José L Trueba

2006-01-01

124

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

125

Precise Re isotope ratio measurements by negative thermal ionization mass spectrometry (NTI-MS) using total evaporation technique  

Microsoft Academic Search

High precision rhenium isotope ratios, 187Re\\/185Re, have been determined by negative thermal ionization mass spectrometry (NTI-MS) using a total evaporation technique. The salient features of this method are evaporation of the entire sample and simultaneous integration of the signal from each isotope, which effectively eliminates isotope fractionation effects during the evaporation process. The 187Re\\/185Re ratio is obtained with a high

Katsuhiko Suzuki; Yoshiki Miyata; Nobuyuki Kanazawa

2004-01-01

126

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

SciTech Connect

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

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

2010-03-01

127

Electrospray Ionization Mass Spectrometry of Genetically and Chemically Modified Bacteriorhodopsins  

Microsoft Academic Search

A simple method for the preparation of bacteriorhodopsin for mass spectrometry is described, consisting of precipitation of the sample, removal of lipids by washing the sample, and dissolving it in an acidic mixture of organic solvents. Examples demonstrate the method's suitability for the analysis of genetically and chemically modified bacteriorhodopsins. The observed molecular masses are within 0.01% in accordance with

P. Hufnagel; U. Schweiger; C. Eckerskorn; D. Oesterhelt

1996-01-01

128

Determination of stigmasterol and cholesterol oxides using atmospheric pressure chemical ionization liquid chromatography\\/mass spectrometry  

Microsoft Academic Search

A new sensitive HPLC–MS method for the detection of sterol oxidation products was developed. The method was developed and optimized with commercially available cholesterol oxidation products. MS detection was carried out with an ion-trap mass spectrometer using atmospheric pressure chemical ionization in positive ion mode. With this new method, both primary and secondary oxidation products of cholesterol and stigmasterol, including

Suvi Kemmo; Velimatti Ollilainen; Anna-Maija Lampi; Vieno Piironen

2007-01-01

129

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

Microsoft Academic Search

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

Steven B. Hawthorne; David J. Miller

1986-01-01

130

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

Microsoft Academic Search

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

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

2010-01-01

131

Desorption electrospray ionization mass spectrometry in the analysis of chemical food contaminants in food  

Microsoft Academic Search

Since its introduction, desorption electrospray ionization (DESI) mass spectrometry (MS) has been mainly applied in pharmaceutical and forensic analysis. We expect that DESI will find its way in many different fields, including food analysis. In this review, we summarize DESI developments aimed at controlling chemical contaminants in food. Data are given for analysis of pesticides, natural toxins, veterinary drugs, food

M. W. F. Nielen; H. Hooijerink; P. Zomer; J. G. J. Mol

2011-01-01

132

Ionization mechanisms in CRRES chemical releases 1. In situ measurements and model results  

NASA Astrophysics Data System (ADS)

The quadrupole ion mass spectrometer (QIMS) measured fluxes of barium and strontium ions during the CRRES G-1 chemical release in full Sun and the G-11b release in darkness. The barium ion fluxes detected in darkness were only a factor of 10 lower than the photoionization fluxes, indicating that the rate of nonsolar-UV ionization was at least a factor of 8 higher than literature values of charge transfer and collisional ionization cross sections would suggest. Model calculations of the QIMS ion fluxes using new, state-specific, calculations of the cross sections for ion-pair formation and charge transfer [Wolf and Hunton, this issue] demonstrate that the large nonphotoionization rates are consistent with significant metastable excitation in the neutral cloud but not with a ground state population. Upper limits to the collisional ionization rates for the conditions of the releases are 4.3×10-3s-1 for ion-pair production and 2.2×10-3s-1 for charge transfer. Collisions of high-energy electrons with the neutrals early in the cloud expansion is suggested as a mechanism for producing the metastable metal atoms. A similar analysis of the strontium data indicates that photoionization, charge transfer, and collisional ion-pair production alone cannot explain the large fluxes of strontium ions detected in the sunlit release. Associative ionization may therefore be an important ionization mechanism for that metal in sunlight. The implications of these results for analysis of space critical ionization velocity experiments are discussed.

Hunton, D. E.; Wolf, P. J.; Shadid, T. M.

1998-01-01

133

[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

134

Development of methane positive chemical ionization gas chromatography/mass spectrometry procedures to determine polychlorinated biphenyls  

SciTech Connect

Positive ion chemical ionization GC/MS was evaluated for the quantitation of polychlorobiphenyls (PCBs) using 10 or less selected PCB standards. Positive ion chemical ionization MS conditions were found that resulted in the best sensitivity and least fragmentation for the PCBs. The optimal conditions were a source temperature of 100 /sup 0/C and source pressure of 0.6 torr, using 200 eV of energy. Mass spectral and response factor (RF) information was gathered for 137 pure cogeners to evaluate methodology of grouping PCBs by level of chlorination or by clustering according to similar responses for quantitation using 10 or less standards. Positive methane chemical ionization was well-suited for their analysis, since the RF values only varied by a factor of 12 at extremes and the technique was 2-6 times more sensitive than electron impact ionization. It was determined that quantitation by using a standard from each level of chlorination showed an overall mean deviation of 21%. It proved more useful for analysis of environmental samples than the cluster scheme, which required isomer identification for proper classification of the PCB to a cluster. The analysis of a sediment extract spiked with PCB congeners resulted in a 14% +/- 5% deviation between actual concentrations and measured concentrations using PCB standards at each level of chlorination. 24 references, 6 figures, 6 tables.

Voyksner, R.D.; Bursey, J.T.; Pack, T.W.; Porch, R.L.

1986-03-01

135

Negative thermal ionization mass spectrometry of main group elements Part 2. 6th group: sulfur, selenium and tellurium  

NASA Astrophysics Data System (ADS)

A systematic investigation of the formation of negative ions for the 6th main group elements using negative thermal ionization mass spectrometry (NTI-MS) is presented. A double-filament ion source with BaO on the ionization filament has been applied to reduce the work function of the rhenium filament material. S[radical sign]-, Se[radical sign]- and Te[radical sign]- were produced as most abundant ions. Low intensities of SeO[radical sign]-, SeO[radical sign]-2, TeO[radical sign]- and TeO[radical sign]-2 have also been detected. Although the electron affinity of SO2 is low, high ion currents of SO[radical sign]-2 have been observed from BaSo4 samples. This may be due to an electron capture process of this molecule rather than to a thermal ionization process. A silica gel suspension mixed with the sample enhanced the Se[radical sign]- ion current by a factor of about 40 and the Te[radical sign]- intensity by a factor of about 10. However, the silica gel showed no enhancing effect on the S[radical sign]- ion current. An improvement in the precision of the selenium and tellurium isotope ratio measurements by a factor of up to 10 was obtained when using the silica gel technique as compared with previous NTI investigations. The data of the selenium isotope abundance measurements were accepted as "best measurements" by the IUPAC.

Wachsmann, M.; Heumann, K. G.

1992-05-01

136

Determination of urinary phytoestrogens by HPLC–MS\\/MS: A comparison of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI)  

Microsoft Academic Search

A comparison of the analytical performance of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) for the quantitative determination of six urinary phytoestrogens (daidzein, O-desmethylangolensin, equol, enterodiol, enterolactone and genistein) by high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS\\/MS) is presented here. Both APCI and ESI were suitable for the analysis of these compounds; however, ESI did improve measurement imprecision and

Michael E. Rybak; Daniel L. Parker; Christine M. Pfeiffer

2008-01-01

137

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

Microsoft Academic Search

The ionization pathways were determined for sets of isomeric non-polar hydrocarbons (structural isomers, cis\\/trans isomers)\\u000a using ion mobility spectrometry and mass spectrometry with different techniques of atmospheric pressure chemical ionization\\u000a to assess the influence of structural features on ion formation. Depending on the structural features, different ions were\\u000a observed using mass spectrometry. Unsaturated hydrocarbons formed mostly [M ? 1]+ and

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

2002-01-01

138

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

SciTech Connect

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

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

2011-04-28

139

Chemical ionization tandem mass spectrometer for the in situ measurement of methyl hydrogen peroxide  

SciTech Connect

A new approach for measuring gas-phase methyl hydrogen peroxide [(MHP) CH{sub 3}OOH] utilizing chemical ionization mass spectrometry is presented. Tandem mass spectrometry is used to avoid mass interferences that hindered previous attempts to measure atmospheric CH{sub 3}OOH with CF{sub 3}O{sup -} clustering chemistry. CH{sub 3}OOH has been successfully measured in situ using this technique during both airborne and ground-based campaigns. The accuracy and precision for the MHP measurement are a function of water vapor mixing ratio. Typical precision at 500 pptv MHP and 100 ppmv H{sub 2}O is {+-}80 pptv (2 sigma) for a 1 s integration period. The accuracy at 100 ppmv H{sub 2}O is estimated to be better than {+-}40%. Chemical ionization tandem mass spectrometry shows considerable promise for the determination of in situ atmospheric trace gas mixing ratios where isobaric compounds or mass interferences impede accurate measurements.

St Clair, Jason M.; McCabe, David C. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 (United States); Crounse, John D. [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States); Steiner, Urs [Varian, Inc., Santa Clara, California 95051 (United States); Wennberg, Paul O. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 (United States); Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125 (United States)

2010-09-15

140

Ionization mechanisms in CRRES chemical releases 1. In situ measurements and model results  

Microsoft Academic Search

The quadrupole ion mass spectrometer (QIMS) measured fluxes of barium and strontium ions during the CRRES G-1 chemical release in full Sun and the G-lib release in darkness. The barium ion fluxes detected in darkness were only a factor of 10 lower than the photoionization fluxes, indicating that the rate of nonsolar-UV ionization was at least a factor of 8

D. E. Hunton; P. J. Wolf; T. M. Shadid

1998-01-01

141

Ionization mechanisms in CRRES chemical releases 1. In situ measurements and model results  

Microsoft Academic Search

The quadrupole ion mass spectrometer (QIMS) measured fluxes of barium and strontium ions during the CRRES G-1 chemical release in full Sun and the G-11b release in darkness. The barium ion fluxes detected in darkness were only a factor of 10 lower than the photoionization fluxes, indicating that the rate of nonsolar-UV ionization was at least a factor of 8

D. E. Hunton; P. J. Wolf; T. M. Shadid

1998-01-01

142

Quantitative analysis of plasma acylcarnitines using gas chromatography chemical ionization mass f rag mentog rap hy  

Microsoft Academic Search

A stable isotope dilution gas chromatography chemical ionization mass spectrometry (GC-CI-MS) method was developed for the quantitative profiling of plasma acylcar- nitines. The clean-up procedure was comprised of a solid- phase cation exchange extraction using PRScolumns from which the acylcarnitines were eluted with a barium chloride solution. Isolated acylcarnitines were transformed into acylox- ylactones and analyzed by positive GC-CI-MS using

C. G. Costa; E. A. Stnays; A. Bootsma; H. J. ten Brink; L. Dorland; I. Tavares de Almeida; M. Duran; C. Jakobs

143

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

144

Bimolecular and unimolecular contributions to the disparate self-chemical ionizations of ? Pinene and camphene isomers  

Microsoft Academic Search

The contributions of molecular and fragment ions toward the disparate self-chemical ionization (SCI) of ?-pinene and camphene isomers were investigated. A kinetic model was constructed to predict the SCI outcomes for these two\\u000a C10H16 isomers. A major portion of the camphene molecular ions (isolated 500 ms after the 10 ms EI event at 24 eV) unimolecularly\\u000a dissociated within 200 s

Touradj Solouki; Jan E. Szulejko

2007-01-01

145

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

146

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

147

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

Microsoft Academic Search

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

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

2011-01-01

148

Virtual quantification of metabolites by capillary electrophoresis-electrospray ionization-mass spectrometry: predicting ionization efficiency without chemical standards.  

PubMed

A major obstacle in metabolomics remains the identification and quantification of a large fraction of unknown metabolites in complex biological samples when purified standards are unavailable. Herein we introduce a multivariate strategy for de novo quantification of cationic/zwitterionic metabolites using capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) based on fundamental molecular, thermodynamic, and electrokinetic properties of an ion. Multivariate calibration was used to derive a quantitative relationship between the measured relative response factor (RRF) of polar metabolites with respect to four physicochemical properties associated with ion evaporation in ESI-MS, namely, molecular volume (MV), octanol-water distribution coefficient (log D), absolute mobility (mu(o)), and effective charge (z(eff)). Our studies revealed that a limited set of intrinsic solute properties can be used to predict the RRF of various classes of metabolites (e.g., amino acids, amines, peptides, acylcarnitines, nucleosides, etc.) with reasonable accuracy and robustness provided that an appropriate training set is validated and ion responses are normalized to an internal standard(s). The applicability of the multivariate model to quantify micromolar levels of metabolites spiked in red blood cell (RBC) lysates was also examined by CE-ESI-MS without significant matrix effects caused by involatile salts and/or major co-ion interferences. This work demonstrates the feasibility for virtual quantification of low-abundance metabolites and their isomers in real-world samples using physicochemical properties estimated by computer modeling, while providing deeper insight into the wide disparity of solute responses in ESI-MS. New strategies for predicting ionization efficiency in silico allow for rapid and semiquantitative analysis of newly discovered biomarkers and/or drug metabolites in metabolomics research when chemical standards do not exist. PMID:19275147

Chalcraft, Kenneth R; Lee, Richard; Mills, Casandra; Britz-McKibbin, Philip

2009-04-01

149

Use of Negative Air Ionization for Reducing Microbial Contamination on Stainless Steel Surfaces  

Microsoft Academic Search

SUMMARY Microbiological concerns in food plant sanitation that relies heavily on physical and chemical methods for removing and killing bacteria could be reduced by the use of non-chemical intervention methods. This initial work on the effects of electrostatic space charge on biofilms shows promise as a viable intervention option for reducing bacterial contamination on surfaces. Natural bacterial populations from a

J. W. Arnold; B. W. Mitchell

2002-01-01

150

Chemical reactions in the plasma active medium of a cw electron-beam-ionization CO/sub 2/ laser  

SciTech Connect

A study of the chemical changes in the composition of the plasma laser mixture which occurs during prolonged operation of a technological cue electron-beam-ionization CO/sub 2/ laser is reported. (AIP)

Averin, A.; Basov, N.; Glotov, E.; Danilychev, V.; Leonov, Y.; Sazhina, N.; Soroka, A.; Yugov, V.

1981-07-01

151

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...

152

Rapid Analysis of Chemical Warfare Agents and Their Hydrolysis Products by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS).  

National Technical Information Service (NTIS)

A 'dip and shoot' analytical method was developed for the rapid sampling and desorption electrospray ionization mass spectrometric (DESI-MS) analysis of chemical warfare agents and their hydrolysis products in liquid samples. Sampling was performed by sim...

C. L. Chenier P. A. D'Agostino

2009-01-01

153

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

PubMed Central

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

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

2010-01-01

154

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

PubMed

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

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

2011-07-30

155

Determination of double bond position in conjugated dienes by chemical ionization mass spectrometry with isobutane  

SciTech Connect

The chemical ionization (CI) mass spectra of a series of functionalized conjugated dienes, including aldehydes, alcohols, formates, acetates, and hydrocarbons were investigated to determine whether fragmentations occur that are characteristic of the position of the conjugated system within the hydrocarbon chain. CI with isobutane as ionizing gas produces structure-specific fragment ions with m/z ratios that can be used to locate the positions of the double bonds in most of the cases studied. When the conjugated system is proximal to the functional group or conjugated with the functional group, other fragmentation processes take precedence. These patterns of fragmentations constitute a very useful analytical tool for the location of conjugated double bonds in a variety of natural products. 34 references, 3 tables, 3 figures.

Doolittle, R.E.; Tumlinson, J.H.; Proveaux, A.

1985-07-01

156

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

157

Characterization of aluminum species with nitrate, perchlorate and sulfate ions in the positive and negative ion mode by electrospray ionization mass spectrometry.  

PubMed

The application of electrospray ionization mass spectrometry (ESI-MS) for aluminum speciation in the positive and negative ion modes was discussed. Aluminum nitrate, perchlorate and sulfate solutions were measured by ESI-MS. In the positive ion mode, aluminum species containing anions (Al-L; L=NO3, ClO4 and SO4) were identified, while [Al(OH)2(H2O)n]+ (n=2-4) were the main species. The affinity of the anions with Al3+ estimated by ESI-MS was consistent with the hardness of the anions (hard and soft acids and bases principle) and the results from 27Al nuclear magnetic resonance studies. This indicates that the results observed from the positive ion mode preserved the chemical state of aluminum in the solution. In the negative ion mode, [Al(OH)4-nLn]- (n=0-2, L=NO3, ClO4) were the main species, which were considered to be converted from positive aluminum species, [Al(OH)(H2O)n]+ (n=2-4), by the successive addition of anions. Anions did not only attach to one aluminum ion but also bridged two aluminum ions. In Al2(SO4)3 solution, the behavior of SO4(2-) in the negative ion mode differed from that of NO3- and ClO4-. This may reflect the affinity of SO4(2-) with Al3+ in the solution or in the mass spectrometer or in both. Finally, detection mechanisms for the aluminum species in the solution are proposed for both the positive and negative ion modes. It is shown that ESI-MS can be used to observe the interaction between Al3+ and anions. We show the importance of the interpretation of the results by ESI-MS for obtaining new information of the metal species in the solution. PMID:18946873

Urabe, Tatsuya; Tsugoshi, Takahisa; Tanaka, Miho

2009-02-01

158

Negative thermal ionization mass spectrometry of selenium part 3.* Selenium trace determination in food samples  

Microsoft Academic Search

Summary Selenium traces are analysed in different animal tissue samples with isotope dilution mass spectrometry using the formation of negative Se- thermal ions (NTI-IDMS) for isotope ratio measurements. An enriched82Se spike is applied for the isotope dilution technique. After decomposition of the food samples with a HNO3\\/HCIO4 mixture selenium is separated by the formation of SeH2 using a hydride generation

Klaus G. Heumann; Norbert Rädlein

1989-01-01

159

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

160

Determination of daminozide in apples by gas chromatography/chemical ionization mass spectrometry.  

PubMed

A method using gas chromatography/chemical ionization mass spectrometry (GC/CIMS) for the determination of daminozide residues in apples has been developed. Daminozide was separated from the sample matrix by water extraction and cation exchange, converted to the methyl ester by treatment with HCl-methanol, and determined by GC/CIMS using succinonitrile as an internal standard. The detection level was 0.05 ppm. Recoveries were 92-104% from apples spiked at the 0.05-0.5 ppm levels. Of the 25 apple samples analyzed, only 2 were positive for daminozide (1.04 and 0.32 ppm). PMID:2592322

Liu, C H; Mattern, G C; Singer, G M; Rosen, J D

161

The identification of bile acid methyl esters by gas chromatography methane chemical ionization mass spectrometry.  

PubMed

Methane chemical ionization mass spectrometric data and gas chromatography retention parameters are reported for 31 bile acid methyl esters. The group includes both saturated and unsaturated compounds with up to three keto or hydroxyl groups. Major ions include the quasimolecular ions and fragments resulting from the loss of neutral species such as methanol, water and methane. The combination of gas-liquid chromatography retention and mass spectral data is sufficient for an unequivocal distinction among all the bile acids studied. Application of this data to the identification of bile acid metabolites is cited. PMID:476290

Muschik, G M; Wright, L H; Schroer, J A

1979-06-01

162

Low blank rhenium isotope ratio determinations by V2O5 coated nickel filaments using negative thermal ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Thenium isotope ratio determinations are, in principle, possible by negative thermal ionization mass spectrometry (NTI-MS). Relatively high rhenium blanks from the commonly-used filament materials prevent accurate isotope ratio determinations, especially for small rhenium sample amounts which are of importance, for example, in geochronology in connection with the Re/Os dating method. Platinum and nickel filaments were tested by different preparation techniques to reduce the rhenium blank contribution from the filament material. The lowest rhenium blank of less than 1 pg was achieved by coating nickel filaments with V2O5 prior to degassing under high vacuum conditions at 850°C. Obviously, the vanadium--nickel oxide layer formed on the surface of the filament during this process prevents further emission of rhenium ions from the filament material. Using Ba(OH)2 for the enhancement of negative thermal ions, 1 ng of rhenium resulted in ion currents at the detector side of about 10-11 A with an ionization efficiency of up to 20%. The 185Re/187Re isotope ratio of a sample of natural isotopic composition could be determined to be 0.59818 ± 0.00026 with a relative precision of 0.04%. The isotope ratio determination for an 187Re spike was comparable in precision but the relative standard deviation of an 185Re spike was significantly higher, which could be explained by mass fractionations of oxygen in the measured ReO-4 ion. The ReO-4 ion is about 200 to 2500 times more abundant than the only other detectable rhenium ion in NTI-MSReO-3. The ReO-4/ReO-4 ratio decreases with increasing temperature. By the low blank NTI-MS technique described in this work, more precise and accurate determinations of the rhenium isotope ratio and the rhenium concentration by isotope dilution analysis from nanogramme samples are possible.

Walczyk, Thomas; Hebeda, Erhard H.; Heumann, Klaus G.

1994-02-01

163

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

NASA Astrophysics Data System (ADS)

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

Pan, Xiang

164

Picoelectrospray Ionization Mass Spectrometry Using Narrow-Bore Chemically Etched Emitters  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

165

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

166

Positive and negative-mode laser desorption/ionization-mass spectrometry (LDI-MS) for the detection of indigoids in archaeological purple.  

PubMed

Laser-based ionization techniques have demonstrated to be a valuable analytical tool to study organic pigments by mass spectrometric analyses. Though laser-based ionization techniques have identified several natural and synthetic organic dyes and pigments, they have never been used in the characterization of purple. In this work, positive and negative-mode laser desorption/ionization mass spectrometry (LDI-MS) was used for the first time to detect indigoids in shellfish purple. The method was used to study organic residues collected from archaeological ceramic fragments that were known to contain purple, as determined by a classical high-performance liquid chromatography-based procedure. LDI-MS provides a mass spectral fingerprint of shellfish purple, and it was found to be a rapid and successful tool for the identification of purple. In addition, a comparison between positive and negative mode ionization highlighted the complementarity of the two ionization modes. On the one hand, the negative-ion mode LDI-MS showed a better selectivity and sensitivity to brominated molecules, such as 6,6'-dibromoindigo, 6-monobromoindigo, 6,6'-dibromoindirubin, 6- and 6'-monobromoindirubin, thanks to their electronegativity, and produced simpler mass spectra. On the other hand, negative-ion mode LDI-MS was found to have a lower sensitivity to non-brominated compounds, such as indigo and indirubin, whose presence can be established in any case by collecting the complementary positive-ion LDI mass spectrum. PMID:23494796

Ribechini, Erika; Pérez-Arantegui, Josefina; Colombini, Maria Perla

2013-03-01

167

Differentiation of human kidney stones induced by melamine and uric acid using surface desorption atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Clinically obtained human kidney stones of different pathogenesis were dissolved in acetic acid/methanol solutions and then rapidly analyzed by surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS) without any desalination treatment. The mass spectral fingerprints of six groups of kidney stone samples were rapidly recorded in the mass range of m/z 50-400. A set of ten melamine-induced kidney stone samples and nine uric acid derived kidney stone samples were successfully differentiated from other groups by principal component analysis of SDAPCI-MS fingerprints upon positive-ion detection mode. In contrast, the mass spectra recorded using negative-ion detection mode did not give enough information to differentiate those stone samples. The results showed that in addition to the melamine, the chemical compounds enwrapped in the melamine-induced kidney stone samples differed from other kidney stone samples, providing useful hints for studying on the formation mechanisms of melamine-induced kidney stones. This study also provides useful information on establishing a MS-based platform for rapid analysis of the melamine-induced human kidney stones at molecular levels. PMID:21394847

Jia, Bin; Ouyang, Yongzhong; Sodhi, Rana N S; Hu, Bin; Zhang, Tingting; Li, Jianqiang; Chen, Huanwen

2011-03-01

168

Determination of MK-287, a new platelet-activating factor antagonist, in plasma and serum by gas chromatography chemical ionization mass spectrometry.  

PubMed

MK-287 is a novel platelet-activating factor antagonist. A sensitive and specific gas chromatographic/mass spectrometric assay has been developed for the determination of the drug in serum and plasma. The assay utilizes an extraction with methyl-t-butyl ether and subsequent trimethylsilylation of the hydroxyl function. The gas chromatographic/mass spectrometric determinations are carried out with temperature-programmed capillary gas chromatography and ammonia negative chemical ionization mass spectrometry. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of drug concentrations in clinical samples. PMID:1932155

Fisher, A L; Morris, M J; Gilbert, J D

1991-07-01

169

Long-range attraction of negatively charged dust particles in weakly ionized dense dust clouds  

NASA Astrophysics Data System (ADS)

The new Plasma Kristall Experiment (PK-4) is scheduled to fly on the International Space Station in 2012 with one of the experiments designed to investigate the existence of two fluid phases and a critical point in complex plasmas. A crucial issue is the parameter regime where the critical point could be found and this requires, as a first step, knowledge of the parameter range where dust-dust attraction can exist. This problem is addressed in the present work, extending previous works on long-range screening and attraction of negatively charged dust particles in plasmas. The roles of nonlinearities, ion-neutral collisions, electron dynamics, and plasma source on the depth and long-range behavior of the attractive well are established and the impact of these results on the PK-4 experiments is discussed.

de Angelis, U.; Regnoli, G.; Ratynskaia, S.

2010-04-01

170

Comprehensive chemical analysis of Venenum Bufonis by using liquid chromatography/electrospray ionization tandem mass spectrometry.  

PubMed

A rapid, sensitive and versatile liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for the comprehensive analyses of the chemical constituents contained in the Chinese medicine-Venenum Bufonis (VB, Chan' Su in Chinese). LC analysis was carried out on an Agilent Eclipse plus C?? RRHD column (2.1 × 150 mm, 1.8 ?m) with a linear gradient solvent system of water (0.1% formic acid) and acetonitrile (0.1% formic acid) as mobile phase. Detection and quantification were performed by multiple reaction monitoring (MRM) transitions via electrospray ionization (ESI) source operating in the positive ionization mode. Through "Molecular Feature Extraction" (MFE), more than 900 features were detected from VB extracts. Among them, a total of 97 components were identified using the Agilent METLIN accurate mass matching database (DB) established according to those reported in the literatures. Further more, 30 high quality matches were obtained by comparisons of their accurate mass and retention times (AMRT) with those imported out in the developed personal database (METLIN DB with AMRT). The characteristic fragmentation pathways were proposed for the tentative characterization of four representative types of bufadienolides in the present work. The targeted MS/MS experiment of the 30 major compounds was performed for their quantification and semi-quantification. And 7 of them were quantified over the assaying concentration range of 5.0-500 pg/?L. The lowest limit of detection and quantification of them were 0.25-0.50 and 1.25-0.25 pg/?L, respectively. The recoveries varied from 83 to 106% depending on the chemical types and different extraction solvents. The remained 23 bufosteroids were simultaneously semi-quantified using three representative standard compounds as their standard references, respectively. PMID:21696903

Hu, Yongmei; Yu, Zhiling; Yang, Zhi Jun; Zhu, Guoyuan; Fong, Wangfun

2011-05-20

171

Molecular Surface Sampling and Chemical Imaging using Proximal Probe Thermal Desorption/Secondary Ionization Mass Spectrometry  

SciTech Connect

Proximal probe thermal desorption/secondary ionization mass spectrometry was studied and applied to molecular surface sampling and chemical imaging using printed patterns on photopaper as test substrates. With the use of a circular cross section proximal probe with a tip diameter of 50 m and fixed temperature (350 C), the influence of probe-to-surface distance, lane scan spacing, and surface scan speed on signal quality and spatial resolution were studied and optimized. As a compromise between signal amplitude, signal reproducibility, and data acquisition time, a surface scan speed of 100 m/s, probe-to-paper surface distance of 5 m, and lane spacing of 10 m were used for imaging. Under those conditions the proximal probe thermal desorption/secondary ionization mass spectrometry method was able to achieve a spatial resolution of about 50 m as determined by the ability to distinguish surface patterns of known dimensions that were printed on the paper substrate. It is expected that spatial resolution and chemical image quality could be further improved by using probes of smaller cross section size and by incorporating a means to maintain a fixed optimal probe-to-surface distance real time, continuously adapting to the changing topography of the surface during a lane scan.

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

2011-01-01

172

Atmospheric pressure chemical ionization mass spectrometry of pyridine and isoprene: potential breath exposure and disease biomarkers.  

PubMed

Volatile organic compounds (VOCs) in exhaled human breath can serve as potential disease-specific and exposure biomarkers and therefore can reveal information about a subject's health and environment. Pyridine, a VOC marker for exposure to tobacco smoke, and isoprene, a liver disease biomarker, were studied using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). While both molecules could be detected in low-ppb levels, interactions of the ionized analytes with their neutral forms and ambient air led to unusual ion/molecule chemistry. The result was a highly dynamic system and a nonlinear response to changes in analyte concentration. Increased presence of ambient water was found to greatly enhance the detection limit of pyridine and only slightly decrease that of isoprene. APCI-MS is shown to be a promising analytical tool in breath analysis with good detection limits, but its application requires a better understanding of the ion/molecule chemistry that may affect VOC quantification from a chemically complex system such as human breath. PMID:23579200

Kapishon, Vitaliy; Koyanagi, Gregory K; Blagojevic, Voislav; Bohme, Diethard K

2013-04-12

173

Single photon ionization and chemical ionization combined ion source based on a vacuum ultraviolet lamp for orthogonal acceleration time-of-flight mass spectrometry.  

PubMed

A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 10(11) photons s(-1), while the CI was achieved through ion-molecule reactions with O(2)(+) reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface. PMID:21591696

Hua, Lei; Wu, Qinghao; Hou, Keyong; Cui, Huapeng; Chen, Ping; Wang, Weiguo; Li, Jinghua; Li, Haiyang

2011-06-02

174

Static diode pumped alkali lasers: Model calculations of the effects of heating, ionization, high electronic excitation and chemical reactions  

NASA Astrophysics Data System (ADS)

The effects of heating, ionization, high electronic excitation and chemical reactions on the operation of diode pumped alkali lasers (DPALs) with a static, non-flowing gain medium are calculated using a semi-analytical model. Unlike other models, assuming a three-level scheme of the laser and neglecting influence of the temperature on the lasing power, it takes into account the temperature rise and losses of neutral alkali atoms due to ionization and chemical reactions, resulting in decrease of the pump absorption and slope efficiency. Good agreement with measurements in a static DPAL [B.V. Zhdanov, J. Sell, R.J. Knize, Electron. Lett. 44 (2008) 582] is obtained. It is found that the ionization processes have a small effect on the laser operation, whereas the chemical reactions of alkali atoms with hydrocarbons strongly affect the lasing power.

Barmashenko, B. D.; Rosenwaks, S.; Heaven, M. C.

2013-04-01

175

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

Microsoft Academic Search

The analysis of complex mixtures of chlorinated paraffins (CPs) with short (SCCPs, C 10–C 13) and medium (MCCPs, C 14–C 17) chain lengths can be disturbed by mass overlap, if low resolution mass spectrometry (LRMS) in the electron capture negative ionization mode is employed. This is caused by CP congeners with the same nominal mass, but with five carbon atoms

Margot Reth; Michael Oehme

2004-01-01

176

Chemical equilibrium between excitons, electrons, and negatively charged excitons in semiconductor quantum wells  

NASA Astrophysics Data System (ADS)

The principle of chemical equilibrium is found to govern formation of negatively charged excitons (X-) by excitons (X) and free electrons (e-). An optical spectroscopy study of undoped CdTe/Cd0.88Mn0.12Te double quantum wells (QW's) revealed formation of a negatively charged exciton state in the thicker QW due to the interwell tunneling of photoexcited electrons. A peculiar, nonmonotonic behavior of the ratio of X to X- densities as a function of the excitation density evidenced that the chemical law of action of masses corresponding to the reaction X+e-<==>X- is fulfilled.

Siviniant, J.; Scalbert, D.; Kavokin, A. V.; Coquillat, D.; Lascaray, J.-P.

1999-01-01

177

Mechanism of porphyrin reduction and decomposition in a high-pressure chemical ionization plasma  

SciTech Connect

Mechanisms for the in situ reduction and decomposition of porphyrins that occur in a high-pressure ammonia and hydrogen chemical ionization (CI) plasma are proposed based on studies of selected model porphyrins and porphyrinogens, both in a high-pressure Cl ion source and under low-pressure CI conditions in a three-dimensional quadrupole ion trap. Stepwise reduction of the porphyrin by radical hydrogen, aided by interaction of the porphyrin with the interior surfaces of the ion source, followed by ionization, forms molecular species, (M + nH){sup +}, where n = 0, 2, 4, and 6 when using hydrogen, and where n = 1,3,5, and 7 when using ammonia. The major fragment ions in the CI mass spectra, although arising from the reduced molecular species, are not products of simple unimolecular dissociation of the (M + nH){sup +} species. Mass spectrometry/mass spectrometry (MS/MS) studies show that the (M + nH){sup +} species, where n {>=} 2, fragment to form tri-, di-, and monopyrrolic units with masses two or more mass units less than the most abundant pyrrolic fragment ions observed in the CI mass spectra. Therefore, gas-phase unimolecular decomposition of the reduced ionic species can contribute somewhat to the overall CI mass spectrum. However, the major pyrrolic fragment ions observed in these spectra (as well as the majority of the other fragments) more likely result from unimolecular and thermal decomposition of the reduced species (both ionic and neutral) in the gas-phase and on the source surfaces, forming neutrals that possibly undergo additional reactions in the CI plasma prior to ionization.

Van Berkel, G.J.; Glish, G.L.; McLuckey, S.A. (Oak Ridge National Lab., TN (USA)); Tuinman, A.A. (Univ. of Tennessee, Knoxville (USA))

1989-08-02

178

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

179

Airborne observations of formic acid using a chemical ionization mass spectrometer  

NASA Astrophysics Data System (ADS)

The first airborne measurements of formic acid mixing ratios over the United Kingdom were measured on the FAAM BAe-146 research aircraft on 16 March 2010 with a chemical ionization mass spectrometer using I- reagent ions. The I- ionization scheme was able to measure formic acid mixing ratios at 1 Hz in the boundary layer. In-flight standard addition calibrations from a formic acid source were used to determine the instrument sensitivity of 35 ± 6 ion counts pptv-1 s-1 and a limit of detection of 25 pptv. Routine measurements were made through a scrubbed inlet to determine the instrumental background. Three plumes of formic acid were observed over the UK, originating from London, Humberside and Tyneside. The London plume had the highest formic acid mixing ratio throughout the flight, peaking at 358 pptv. No significant correlations of formic acid with NOx and ozone were found, but a positive correlation was observed between CO and HCOOH within the two plumes where coincident data were recorded. A trajectory model was employed to determine the sources of the plumes and compare modelled mixing ratios with measured values. The model underestimated formic acid concentrations by up to a factor of 2. This is explained by missing sources in the model, which were considered to be both primary emissions of formic acid of mainly anthropogenic origin and a lack of precursor emissions, such as isoprene, from biogenic sources, whose oxidation in situ would lead to formic acid formation.

Le Breton, M.; McGillen, M. R.; Muller, J. B. A.; Bacak, A.; Shallcross, D. E.; Xiao, P.; Huey, L. G.; Tanner, D.; Coe, H.; Percival, C. J.

2012-12-01

180

Chemical ionization mass spectrometry for selective detection and analysis of components in complex mixtures  

SciTech Connect

Selectivity and sensitivity in chemical ionization mass spectrometry (CIMS) are determined by the rate constants for the ion/molecule reactions of the CI reagent ions with sample molecules, which are generally simple reactions like proton transfer, hydride transfer, or electron transfer. The rate constants for these reactions of the CI reagent ions with sample molecules are generally large if the reactions are exothermic and consequently the molar sensitivities with the samples are high. However, if these reactions are endothermic, the rate constants are very small and the molar sensitivities are essentially zero. Benzene is a selective CI reagent gas for the detection of unsaturated compounds in complex hydrocarbon mixtures by GC/CIMS and probe distillation CIMS because C{sub 6}H{sub 6}{sup +} reacts rapidly by electron transfer only with compounds with ionization potentials lower than that of benzene. NH{sub 4}{sup +} reacts rapidly by proton transfer only with polar or strongly basic compounds and can be used for the selective detection of polar compounds in the presence of large amounts of hydrocarbons.

Munson, B. (Univ. of Delaware, Newark (USA))

1989-04-01

181

Surface-activated chemical ionization and cation exchange chromatography for the analysis of enterotoxin A.  

PubMed

Surface-activated chemical ionization (SACI) has been widely used in recent years for the analysis of different compounds (e.g. peptides, street drugs, amino acids). The main benefits of this technology are its high sensitivity and its effectiveness under different chromatographic conditions [i.e. ion exchange chromatography and reversed-phase (RP) chromatography]. Here we used SACI in conjunction with quadrupole time-of-flight mass spectrometry to analyze enterotoxin A, which is produced by Staphylococcus aureus, in milk matrix using both RP and ion exchange chromatographies. SACI had increased sensitivity as compared with electrospray ionization. Moreover, the higher quantitation efficiency of this technique, mainly in terms of limit of detection (0.01 ng/ml), limit of quantitation (0.05 ng/ml), linearity range (0.05-50 ng/ml), matrix effect, accuracy (intraday and interday accuracy errors were 9.2% and 10.3%, respectively) and precision (intraday and interday precision errors were 5.3% and 12.8%, respectively), is shown and discussed. PMID:19753553

Cristoni, Simone; Zingaro, Lorenzo; Canton, Cristina; Cremonesi, Paola; Castiglioni, Bianca; Morandi, Stefano; Brasca, Milena; Luzzana, Massimo; Battaglia, Cristina

2009-10-01

182

Kinetic and thermodynamic control of protonation in atmospheric pressure chemical ionization.  

PubMed

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 (S(n)H(+)) and the analyte having different preferred protonation sites in the liquid phase and gas phase. PMID:23633014

Chai, Yunfeng; Hu, Nan; Pan, Yuanjiang

2013-04-30

183

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

2013-04-01

184

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

185

Chemical ionization mass spectrometry with lithium ion attachment to the molecule  

SciTech Connect

This report describes a new development for chemical ionization mass spectrometry (CIMS) that provides mass spectra consisting of quasi-molecular ions, (M + Li)/sup +/, by lithium ion attachment to the sample molecules (M) under high pressure. Lithium ions are generated by heating lithium oxide in an aluminosilicate matrix in a flowing nitrogen gas stream. Alkali-metal ions attach to the sample in the carrier gas in termolecular reactions to produce (M + Li)/sup +/ ions. The lithium ion CI source is attached to the three-stage differentially pumped mass spectrometer with the first cone aperture (0.5 mm i.d.) through which the product ions enter the mass analysis region. The identification and detection of acetone are described as an example of the utility of this new CI ion source. Analysis of a formulated gas sample with direct introduction to the CI source is also demonstrated.

Fujii, T.; Ogura, M.; Jimba, H.

1989-05-01

186

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

NASA Astrophysics Data System (ADS)

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

Little, James L.; Howard, Adam S.

2013-10-01

187

Demonstration of real-time monitoring of a photolithographic exposure process using chemical ionization mass spectrometry  

SciTech Connect

Silicon wafers are coated with photoresist and exposed to ultraviolet (UV) light in a laboratory to simulate typical conditions expected in an actual semiconductor manufacturing process tool. Air is drawn through the exposure chamber and analyzed using chemical ionization mass spectrometry (CI/MS). Species that evaporate or outgas from the wafer are thus detected. The purpose of such analyses is to determine the potential of CI/MS as a real-time process monitoring tool. Results demonstrate that CI/MS can remotely detect the products evolved before, during, and after wafer UV exposure; and that the quantity and type of products vary with the photoresist coated on the wafer. Such monitoring could provide semiconductor manufacturers benefits in quality control and process analysis. Tool and photoresist manufacturers could also realize benefits from this measurement technique with respect to new tool, method, or photoresist development. The benefits realized can lead to improved device yields and reduced product and development costs.

Mowry, C.D. [Sandia National Labs., Albuquerque, NM (United States). Analytical Chemistry Dept.

1998-02-01

188

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

189

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

PubMed

The use of negative ion monitoring mode with an atmospheric pressure ion mobility orthogonal reflector time-of-flight mass spectrometer [IM(tof)MS] to detect chemical warfare agent (CWA) degradation products from aqueous phase samples has been determined. Aqueous phase sampling used a traditional electrospray ionization (ESI) source for sample introduction and ionization. Certified reference materials (CRM) of CWA degradation products for the detection of Schedule 1, 2, or 3 toxic chemicals or their precursors as defined by the chemical warfare convention (CWC) treaty verification were used in this study. A mixture of six G-series nerve related CWA degradation products (EMPA, IMPA, EHEP, IHEP, CHMPA, and PMPA) and their related collision induced dissociation (CID) fragment ions (MPA and EPA) were found in each case to be clearly resolved and detected using the IM(tof)MS instrument in negative ion monitoring mode. Corresponding ions, masses, drift times, K(o) values, and signal intensities for each of the CWA degradation products are reported. PMID:16413205

Steiner, Wes E; Harden, Charles S; Hong, Feng; Klopsch, Steve J; Hill, Herbert H; McHugh, Vincent M

2006-01-18

190

Precise Re isotope ratio measurements by negative thermal ionization mass spectrometry (NTI-MS) using total evaporation technique  

NASA Astrophysics Data System (ADS)

High precision rhenium isotope ratios, 187Re/185Re, have been determined by negative thermal ionization mass spectrometry (NTI-MS) using a total evaporation technique. The salient features of this method are evaporation of the entire sample and simultaneous integration of the signal from each isotope, which effectively eliminates isotope fractionation effects during the evaporation process. The 187Re/185Re ratio is obtained with a high reproducibility (1.6755+/-0.0014 (2[sigma]), R.S.D.=0.083%, n=28) for 50 pg-1 ng of a Re natural standard using the total evaporation with NTI-MS. This value is within analytical uncertainty of the previously reported accurate 187Re/185Re ratio (1.6740+/-0.0011) adopted by IUPAC as the Re isotopic composition, and is significantly more precise than the ratio obtained from conventional NTI-MS isotopic measurements in our laboratory (1.6772+/-0.0037 (2[sigma]), R.S.D.=0.22%, n=34). Based on these results, the total evaporation technique allows us to precisely determine Re isotope ratios, even for small sample amounts. In addition, this method is effective for highly precise Re abundance determinations using isotope dilution.

Suzuki, Katsuhiko; Miyata, Yoshiki; Kanazawa, Nobuyuki

2004-06-01

191

Determination of glucosinolates in rapeseed and Thlaspi caerulescens plants by liquid chromatography–atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

Liquid chromatography–atmospheric pressure chemical ionization mass spectrometry was used to identify glucosinolates in plant extracts. Optimization of the analytical conditions and the determination of the method detection limit was performed using commercial 2-propenylglucosinolate (sinigrin). Optimal values for the following parameters were determined: nebulization pressure, gas temperature, flux of drying gas, capillar voltage, corona current and fragmentor conditions. The method detection

Roser P. Tolrà; Rosa Alonso; Charlotte Poschenrieder; Damià Barceló; Juan Barceló

2000-01-01

192

In situ measurements of atmospheric nitrous acid by chemical ionization mass spectrometry using chloride ion transfer reactions.  

PubMed

Recently, chemical ionization mass spectrometry (CIMS) has been widely applied to the in situ measurements of atmospheric trace species. In this article, we propose a new chemical ionization scheme using a chloride ion transfer reaction from SO(2)Cl(-) as the reagent ion and discuss the applicability of this technique to the detection of nitrous acid (HONO) in the atmosphere. From laboratory investigations, the detection sensitivity was found to depend on the flow rate of SO(2) introduced into the ion source region and the pressure inside the chemical ionization region, which suggests that the chemical ionization reaction is reversible. The detection sensitivity was well described in terms of the forward and backward rates. The present limit of detection is estimated to be 60 parts per trillion by volume (pptv) for an integration time of 1 min. Improvement of the CIMS instrument would enable the measurements of the daytime level of HONO, which might be less than 50 pptv. In addition, the possibility of the interference is discussed from thermodynamic considerations based on ab initio calculations, and the effects of the sampling artifacts are experimentally quantified. PMID:19746928

Hirokawa, Jun; Kato, Takehiro; Mafuné, Fumitaka

2009-10-15

193

UPTAKE AND ELIMINATION OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS: PART I. MODEL FORMULATION, PARAMETERIZATION, AND BEHAVIOR  

EPA Science Inventory

Effects of pH and alkalinity on uptake and elimination of ionizable organic chemicals at the gills of large rainbow trout were studied. Increased pH reduced uptake rates of weakly-acidic chlorinated phenols and increased that of weakly-basic 3,4-dichlorobenzylamine, indicating gr...

194

On-line derivatization gas chromatography with furan chemical ionization tandem mass spectrometry for screening of amphetamines in urine  

Microsoft Academic Search

A simple alternative method with minimal sample pretreatment is investigated for screening of amphetamines in small volume (using only 20?L) of urine sample. The method is sensitive and selective. The method uses gas chromatography (GC) direct sample introduction (DSI) for on-line derivatization (acylation) of amphetamines to improve sensitivity. Furan as chemical ionization (CI) reagent in conjunction with tandem mass spectrometry

Shin-Hwa Tzing; Anil Ghule; Jen-Yu Liu; Yong-Chien Ling

2006-01-01

195

Townsend discharge nitric oxide chemical ionization gas chromatography/mass spectrometry for hydrocarbon analysis of the middle distillates  

SciTech Connect

Hydrocarbon type analysis of petroleum distillates (350-860 {degrees}F fraction) was performed using Townsend discharge nitric acid chemical ionization gas chromatography/mass spectrometry (TDNOCI GC/MS). Both n and z in the chemical formula, C{sub n}H{sub 2n + z} can be determined. GC separation allows quantification of heteroatom compounds in the presence of aromatics of the same mass. Results are presented for the analysis of feedstocks and hydrotreated products.

Dzidic, I.; Petersen, H.A.; Wadsworth, P.A.; Hart, H.V. [Westhollow Research Center, Houston, TX (United States)

1992-10-01

196

Negative thermoelectric power from large diameter multiwalled carbon nanotubes grown at high chemical vapor deposition temperatures  

NASA Astrophysics Data System (ADS)

Multiwalled carbon nanotubes (MWNTs) have been grown using a standard chemical vapor deposition method, except for varying the growth temperature. Nanotubes grown below 770 °C exhibit typical positive thermoelectric powers, while those grown above have negative values. This behavior is attributed to the larger nanotube diameters observed at higher growth temperatures. Below 770 °C, the average nanotube diameter is about 50 nm, while above, nanotubes reach diameters of 300 nm. This increase in diameter and number of inner shells leads to the intrinsic negative thermoelectric power of the inner nanotube shells becoming larger than the positive thermoelectric power due to oxygen doping on the outer surface of the nanotube. The overall negative thermopower (about -6 ?V/K, compared to +7 ?V/K for smaller diameter nanotubes) can be understood in terms of a parallel conduction model. Our large-diameter multiwalled carbon nanotubes allow the intrinsic negative thermopower of MWNTs to be accessed without requiring specific deoxygenation treatment.

Hewitt, Corey A.; Kaiser, Alan B.; Craps, Matt; Czerw, Richard; Carroll, David L.

2013-08-01

197

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

PubMed

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

2009-04-06

198

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.

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

199

Characterization of a New Cleaning Method Using Electrolytic Ionized Water for Polysilicon Chemical Mechanical Polishing Process  

NASA Astrophysics Data System (ADS)

In trench isolation technology, the surface layers of poly-Si buried in the trench are contaminated with silica particles and chemical impurities by the conventional chemical-mechanical polishing (CMP) method. These contaminations produce some unexpected patterns and crystal defects in the wafer surface layer after oxidation. Furthermore, it is difficult to remove them by the conventional wet cleaning techniques. In this work, we have established a new post-CMP cleaning method, using electrolytic ionized water containing a small quantity of HCl. The anode water is shown to have a cleaning effect on the metallic and organic contamination, whereas the cathode water is shown to have a removing effect on the particles and an etching effect on the poly-Si surface. We present the optimization results of the post-CMP cleaning condition by investigating the surface-related properties by means of a particle counter, ellipsometry, secondly electron microscopy (SEM), atomic force microscopy (AFM), inductively coupled plasma/mass spectroscopy (ICP/MS), and secondary ion mass spectroscopy (SIMS). Our newly established cleaning method is currently applicable to the actual CMP planarization process for VLSI.

Miyashita, Naoto; Uekusa, Shin-ichiro; Katumata, Hiroshi

2002-08-01

200

Chemical characteristics of negative-tone chemically amplified resist for advanced mask making: II  

NASA Astrophysics Data System (ADS)

?We investigated the film property and the lithographic performance of five commercialized NCARs. This report focused on Cr effect and PCD stability which are critical issues on advanced mask making. Results confirmed to solve the Cr effect by controlled dissolution rate of resist film. Furthermore, PCD was occurred by PAG moving and unsuitable reaction in the resist film standing delay time. This report suggests the strategy that was design of chemical structure for the next generation NCARs.

Takeshi, Kazumasa; Tanabe, Masahito; Inokuchi, Daisuke; Fukushima, Yuichi; Okumoto, Yasuhiro; Okuda, Yoshimitsu

2004-10-01

201

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

202

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

203

Alternately Pulsed Nano-electrospray Ionization/Atmospheric Pressure Chemical Ionization for Ion/Ion Reactions in an Electrodynamic Ion Trap  

PubMed Central

The alternate operation of nano-electrospray ionization (nano-ESI) and atmospheric pressure chemical ionization (APCI), using a common atmosphere/vacuum interface and ion path, has been implemented to facilitate ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The ion sources are operated in opposite polarity modes whereby one of the ion sources is used to form analyte ions while the other is used to form reagent ions of opposite polarity. This combination of ion sources is well-suited to implementation of experiments involving multiply charged ions in reaction with singly charged ions of opposite polarity. Three analytically useful ion/ion reactions types are illustrated: the partial deprotonation of a multiply protonated protein, the partial protonation of a multiply deprotonated oligonucleotide, and electron transfer to a multiply protonated peptide. The approach described herein is attractive in that it enables both single proton transfer and single electron transfer ion/ion reaction experiments to be implemented without requiring major modifications to the tandem mass spectrometer hardware. Furthermore, a wide range of reactant ions can be formed with these ionization methods and the pulsed nature of operation appears to lead to no significant compromise in the performance of either ion source.

Liang, Xiaorong; Xia, Yu; McLuckey, Scott A.

2008-01-01

204

Comparative analysis of dioxins and furans by electron impact, high-resolution mass spectrometry and by electron capture, negative ionization, low-resolution mass spectrometry  

Microsoft Academic Search

Electron impact, high resolution mass spectrometry (HRMS) is currently the method of choice for the analysis of polychlorinated dibenso-p-dioxins and dibenzofurans (PCDD\\/F) because of its ability to detect PCDD\\/F in the presence of interfering compounds, such as polychlorinated biphenyls (PCB), which cannot be resolved by low resolution methods. The PDCC\\/F analyses may also be performed using electron capture, negative ionization

C. J. Koester; R. L. Harless; R. A. Hites

1990-01-01

205

Selective detection of unknown organic bromine compounds and quantification potentiality by negative-ion electrospray ionization mass spectrometry with induced in-source fragmentation  

Microsoft Academic Search

For the detection of unknown organic bromine compounds, a liquid chromatography–mass spectrometry (LC-MS) method with negative-ion electrospray ionization (NI-ESI) and induced in-source fragmentation (IISF) was established. After LC separation, the molecules are fragmentized in the source, and bromide is detected via m\\/z 79 and m\\/z 81 based on the isotopic occurrence of bromine. In this way, the retention times of

Alexandra Hütteroth; Anke Putschew; Martin Jekel

2007-01-01

206

Comparison of electrospray ionization, atmospheric pressure chemical ionization, and atmospheric pressure photoionization for the analysis of dinitropyrene and aminonitropyrene LC-MS/MS.  

PubMed

The only relevant source for human exposure to dinitropyrenes is diesel engine emissions. Due to this specificity, dinitropyrenes may be used as biomarkers for monitoring human exposure to diesel engine emissions. Only few analytical methods have been described for the quantitation of dinitropyrenes and their metabolites, aminonitropyrenes, and diaminopyrenes. Therefore, for dinitropyrenes, aminonitropyrenes, and diaminopyrenes were selected as model compounds for the development of a sensitive HPLC-MS/MS method (high performance liquid chromatography coupled to triple quadrupole mass spectrometry) was to quantify polyaromatic amines and nitroarenes in biological matrices was developed optimal methods by comparing electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) sources. Dinitropyrene was not effectively ionized and diaminopyrene yielded mainly [M(.)](+) ions by electrospray ionization. With APCI and APPI, precursor ions of diaminopyrene and aminonitropyrene were [M + H](+) and [M(.)](-) for dinitropyrene. Precursor ions with [M - 30(.)](-) for dinitropyrene and [M - 30 + H](+) for aminonitropyrene were observed. Reversed and normal phase HPLC-MS/MS with ESI, APCI and APPI were optimized separately with respect to unequivocal analyte identification and sensitivity. Normal phase HPLC coupled to APPI-MS/MS gave the highest precision and sensitivity for aminonitropyrene (6%/0.2 pg on column) and dinitropyrene (9%/0.5 pg on column). The limit of detection in spiked rat plasma was 5 pg/100 microL for aminonitropyrene (accuracy 82%) and 10 pg/100 microL for dinitropyrene (accuracy 105%). In plasma of rats treated with dinitropyrene by oral administration, no detectable levels of dinitropyrene but higher aminonitropyrene levels compared with intratracheal instillation were observed. These findings clearly demonstrate that dinitropyrene was absorbed after oral and intratracheal application and that a reduction of nitro groups occurs to a high extent in the reductive environment of the intestine. To our knowledge, this is the first time that aminonitropyrene was observed in plasma after intratracheal or oral administration directly demonstrating the reductive metabolism of dinitropyrene in vivo. PMID:15589761

Straube, Ellen A; Dekant, Wolfgang; Völkel, Wolfgang

2004-12-01

207

Metal nanowire arrays with ultralow or negative effective permittivity for adsorption-based chemical sensing  

Microsoft Academic Search

We investigated wire-mesh media with plasmalike dispersion of dielectric permittivity as a potential medium for nanoplasmonic sensors utilizing adsorption of chemical, biochemical or biological analytes. Such structures belong to the ultra-low refractive index metamaterials and are typically used as one of the building blocks for zero- or negative index metamaterials. We analyzed a 2D array or conductive arrays with either

Z. Jaksic; K. Radulovic; D. Tanaskovic

2008-01-01

208

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

209

Chemical characterization of crude petroleum using nanospray desorption electrospray ionization coupled with high-resolution mass spectrometry.  

PubMed

Nanospray desorption electrospray ionization (nano-DESI) combined with high-resolution mass spectrometry was used for the first time for the analysis of the polar constituents 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 based on their solubility in solvents that are rarely used for petroleum characterization providing better coverage of the crude oil composition as compared to electrospray ionization (ESI). It also enables rapid characterization of water-soluble components of petroleum samples that is difficult to perform using traditional approaches. PMID:22166099

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

2012-01-10

210

Atmospheric pressure-ion drift chemical ionization mass spectrometry for detection of trace gas species.  

PubMed

This paper describes atmospheric pressure-ion drift chemical ionization mass spectrometry (AP-ID-CIMS) for monitoring of ambient trace species. Operation of the drift tube at atmospheric pressure allows a significantly longer ion-molecule reaction time and eliminates dilution of the ambient samples, while a well-defined electric field inside the drift tube provides the benefits to confine the flight path and velocity of reagent/product ions, to break down ion clusters, and to control the ion-molecule reaction time. The AP-ID-CIMS exhibits advantages over the conventional low pressure ID-CIMS and flow tube AP-CIMS, improving the detection sensitivity by 3 orders of magnitude and a factor of 3, respectively. We demonstrate that the AP-ID-CIMS allows quantification of sulfuric acid concentrations and is capable of detecting gaseous sulfuric acid with a detection limit of less than 10(5) molecules cm(-3), on the basis of 3sigma of the baseline noise and an integration time of 12 s. A field evaluation of the AP-ID-CIMS is presented for ambient H(2)SO(4) measurements. PMID:20695435

Zheng, Jun; Khalizov, Alexei; Wang, Lin; Zhang, Renyi

2010-09-01

211

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

212

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

213

Atmospheric pressure chemical ionization-mass spectrometry method to improve the determination of dansylated polyamines.  

PubMed

Determination of polyamine pools is still a step impossible to circumvent in studies aimed at determining the pathophysiological role of natural polyamines. In addition, polyamine measurement in biological fluids and tissues may have clinical relevance, especially in cancer patients. Among the wide panel of analytical methods developed for the quantification of polyamines, high-performance liquid chromatographic (HPLC) separation of polyamines after derivatization with dansyl chloride remains the most commonly used method. In this work, we show that atmospheric pressure chemical ionization-mass spectrometry (MS) can be used to detect and quantify biologically relevant polyamines after dansylation, without chromatographic separation. Positive-ion mass spectra for each dansylated polyamine were generated after optimization by flow injection analysis (FIA). FIA coupled with MS detection by selected ion monitoring greatly increased the sensitivity of the polyamine detection. The method is linear over a wide range of polyamine concentrations and allows detection of quantities as low as 5 fmol. The FIA/MS method is about 50-fold more sensitive than the conventional HPLC/fluorimetry procedure. A good correlation (r>0.98) between these two methods was observed. The FIA/MS method notably reduces the time of analysis per sample to 1.5 min and turns out to be rapid, efficient, cost saving, reproducible, and sufficiently simple to allow its routine application. PMID:12814624

Gaboriau, François; Havouis, René; Moulinoux, Jacques-Philippe; Delcros, Jean-Guy

2003-07-15

214

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. © 2013 The Authors. Journal of Mass Spectrometry published by John Wiley & Sons, Ltd. PMID:24078245

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

2013-09-01

215

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

PubMed

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

Sabo, Martin; Matej?ík, Stefan

2013-10-15

216

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

217

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

218

Photodegradation of secondary organic aerosol generated from limonene oxidation by ozone studied with chemical ionization mass spectrometry  

Microsoft Academic Search

Photodegradation of secondary organic aerosol (SOA) prepared by ozone-initiated oxidation of D-limonene is studied with an action spectroscopy approach, which relies on detection of volatile photoproducts with chemical ionization mass-spectrometry as a function of the UV irradiation wavelength. Efficient photodegradation is observed for a broad range of ozone (0.1-300 ppm) and D-limonene (0.02-3 ppm) concentrations used in the preparation of

X. Pan; J. S. Underwood; J.-H. Xing; S. A. Mang; S. A. Nizkorodov

2009-01-01

219

Characterization of phenolic and secoiridoid aglycons present in virgin olive oil by gas chromatography-chemical ionization mass spectrometry  

Microsoft Academic Search

Olive oil phenolic and secoiridoid compound derivatives were detected by mass spectrometry. Chemical ionization (CI) allowed us to obtain parent ions, that were not detectable in the electron impact mode. CI experiments were performed using either CH4 or NH3 as the reactant gas. Unlike CH4-CI, which fails to give molecular mass information, NH3-CI provided, in all the cases explored, an

Franca Angerosa; Nicola d'Alessandro; Federica Corana; Giorgio Mellerio

1996-01-01

220

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

221

Gas chromatography electron ionization mass spectrometric analysis of O-alkyl methylphosphinates for verification of Chemical Weapons Convention.  

PubMed

We describe the gas chromatography/mass spectrometric (GC/MS) analysis of O-alkyl methylphosphinates (AMPs), which are included in schedule 2B4 chemicals in the Chemical Weapons Convention (CWC). GC/MS analysis of variety of AMPs and their deuterated analogues revealed that their fragmentations were determined by alpha-cleavages, McLafferty +1 and hydrogen rearrangements. Based on the obtained electron ionization mass spectra of AMPs the fragmentation routes were rationalized, which were substantiated by the GC/MS analysis of deuterated analogues. PMID:19679938

Pardasani, Deepak; Kanaujia, Pankaj K; Tak, Vijay; Garg, Prabhat; Mazumder, Avik; Dubey, Devendra K

2009-01-01

222

Sample introduction and pressure measuring system for chemical ionization mass spectrometers  

SciTech Connect

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 Atlas CH-4 mass spectrometer operated at ion source potentials up to 3 kV and pressures up to 3 torr. The same technique has been extended at the University of California, Santa Barbara (UCSB), for use with a VG-Micromass ZAB-2F mass spectrometer operated at source potentials as high as 10 kV and pressures up to 1 torr. The basic features of the design are presented. The sample leak valve which is at ground potential feeds into a glass tube which has been packed with approximately 4 in. of glass wool. The end of this glass tube is in contact with the ion source potential. The authors believe that the glass wool may prevent discharging by reducing the positive ion velocities below that required for the emission of secondary electrons and/or providing a very large surface area which may act as the third body in the ion-electron recombination reaction I/sup +/ + e/sup -/ + M ..-->.. I + M. At UCSB this sample introduction system is used for all gaseous and volatile liquid samples in both EI and CI modes. The only disadvantage with the sample introduction system involves the removal of very polar samples from the glass wool. However, overnight pumping has removed all samples we have used to date.

Illies, A.J. (Univ. of California, Santa Barbara); Bowers, M.T.; Meisels, G.G.

1981-08-01

223

Miniature chemical ionization mass spectrometer for light aircraft measurements of tropospheric ammonia  

NASA Astrophysics Data System (ADS)

Tropospheric ammonia plays important roles in the nucleation, growth, composition, and chemistry of aerosol particles. Unfortunately, high frequency and sensitive measurements of gas phase ammonia are lacking in most airborne-based field campaigns. Chemical ionization mass spectrometers (CIMS) have shown great promise for ammonia measurements, but CIMS instruments typically consume large amounts of power, are highly labor intensive, and are very heavy for most airborne platforms. These characteristics of CIMS instruments severely limit their potential deployment on smaller and lighter aircraft, despite the strong desire for ammonia measurements in atmospheric chemistry field campaigns. To this end, a CIMS ammonia instrument for light aircraft is being developed using a double-focusing, miniature mass spectrometer. The size of the mass spectrometer, comparable to a small apple, allows for higher operating pressures (0.1 mTorr) and lower pumping requirements. Power usage, including pumps and electronics, is estimated to be around 300 W, and the overall instrument including pumps, electronics, and permeation cells is expected to be about the size of a small monitor. The ion source uses americium-241 to generate protonated water ions which proton transfer to form ammonium ions. The ion source is made with commercially available ion optics to minimize machining costs. Mass spectra over its working range (~ 5-120 amu) are well represented by Gaussian shaped peaks. By examining the peak widths as a function of mass location, the resolution of the instrument was determined experimentally to be around 110 (m/delta m). The sensitivity, selectivity, power requirements, size, and performance characteristics of the miniature mass spectrometer will be described along with the possibilities for CIMS measurements on light aircraft.

Silver, J. A.; Bomse, D. S.; Massick, S. M.; Zondlo, M. A.

2003-12-01

224

The ionized gas at the centre of IC 10: a possible localized chemical pollution by Wolf-Rayet stars  

NASA Astrophysics Data System (ADS)

We present results from integral field spectroscopy with the Potsdam Multi-Aperture Spectrograph at the 3.5-m telescope at Calar Alto Observatory of the intense star-forming region [HL90] 111 at the centre of the starburst galaxy IC 10. We have obtained maps with a spatial sampling of 1 × 1 arcsec2= 3.9× 3.9 pc2 of different emission lines and analysed the extinction, physical conditions, nature of the ionization and chemical abundances of the ionized gas, as well determined locally the age of the most recent star formation event. By defining several apertures, we study the main integrated properties of some regions within [HL90] 111. Two contiguous spaxels show an unambiguous detection of the broad He II?4686 emission line, this feature seems to be produced by a single late-type WN star. We also report a probable N and He enrichment in the precise spaxels where the Wolf-Rayet (WR) features are detected. The enrichment pattern is roughly consistent with that expected for the pollution of the ejecta of a single or a very small number of WR stars. Furthermore, this chemical pollution is very localized (˜2 arcsec ˜7.8 pc) and it should be difficult to detect in star-forming galaxies beyond the Local Volume. We also discuss the use of the most common empirical calibrations to estimate the oxygen abundances of the ionized gas in nearby galaxies from 2D spectroscopic data. The ionization degree of the gas plays an important role when applying these empirical methods, as they tend to give lower oxygen abundances with increasing ionization degree. Based on observations collected at the Centro Astrónomico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Plank Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Visiting Astronomer at the Instituto de Astrofísica de Canarias.

López-Sánchez, Á. R.; Mesa-Delgado, A.; López-Martín, L.; Esteban, C.

2011-03-01

225

Is the negative temperature coefficient of the resistivity of the quasicrystals due to chemical disorder?  

PubMed

We have found that the electronic transport of the binary icosahedral (i) Cd-Yb is extremely sensitive to a minute substitution of Mg for Cd atoms; the positive temperature coefficient of the resistivity (TCR) at low temperatures seen in the binary i Cd-Yb disappears by addition of only 0.1 at. % Mg and, moreover, the TCR stays negative well up to 60 at. % Mg. Such sensitiveness of the resistivity in the very dilute Mg concentration region, which is a consequence of the long coherence length (>28 A) of the conduction electrons in the quasiperiodic lattice, has led us to an unexpected conclusion: The negative TCR in the ternary i phase is due to partial chemical disorder; i.e., it is not a consequence of the quasiperiodicity. PMID:12857327

Tamura, R; Araki, T; Takeuchi, S

2003-06-04

226

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

227

Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) Analysis of Organophosphorus Chemical Warfare Agents: Rapid Acquisition of Time-Aligned Parallel (TAP) Fragmentation Data.  

National Technical Information Service (NTIS)

Desorption electrospray ionization-mass spectrometric (DESI-MS) analysis has been applied to the direct analysis of chemical warfare agents spiked on a variety of sample media including soils, water, food products and indoor samples that could be collecte...

C. L. Chanier P. A. D'Aghostino

2010-01-01

228

Characterization of complex assemblages of organic acids in geological samples by negative electrospray ionization mass spectrometry using a double-focusing magnetic sector field mass spectrometer.  

PubMed

Four different geological sample types (a crude oil, a crude oil asphaltene, a reservoir core extract and a reservoir core asphaltene) have been characterized by negative ionization electrospray mass spectrometry at low and high mass resolution using a double-focusing magnetic sector field mass spectrometer. The mass range, shape of the spectra and the signal distribution of the acidic constituents as well as the average molecular weights, the total ion abundance and signal intensity in the spectra were compared for the different sample types. Nominal mass classes have been evaluated and Kendrick mass plots were generated in order to identify homologous series. For the crude oil sample, accurate mass assignments were made by high-resolution double-focusing magnetic sector field mass spectrometry (DFMSFMS) and were compared with those obtained by negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). With both instrument types, compounds with the molecular composition C(n)H(2n+z)O(2), among which carboxylic acids predominated, were the main acidic compound class detectable in negative ESI mass spectra. Good agreement was achieved for the double bond class distribution and the carbon number distribution of the O(2) class. In addition, minor compound classes could be identified using FTICRMS. PMID:20301135

Pötz, Stefanie; Wilkes, Heinz; Witt, Matthias; Horsfield, Brian

2010-04-30

229

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

231

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

232

High-resolution negative-tone chemically amplified i-line resists  

NASA Astrophysics Data System (ADS)

Negative tone chemically amplified i-line resists possess several advantages compared to conventional DNQ-Novolak resist. These advantages include excellent lithographic performance at a fast, tunable photospeed, high transparency, high thermal flow stability and improved etch resistance. An additional advantage of using negative resist of logic applications is that the difference in CD for various features at a fixed dose is small relative to conventional positive resists, allowing the maximum potential for printing these features simultaneously. ULTRA- i 300/310 are negative acting i-line photoresist with excellent lithographic performance optimized for 90 degrees C PAB/110 degrees C PEB processing. These materials offer extremely high resolution capability without microbridging, fast photospeed, and a robust post exposure delay process window with minimal film loss over a period of hours. these resists exhibit extremely low PEB temperature sensitivity which is expected to reduce across chip linewidth variation. Low optical density permits thick film applications producing high aspect ratio relief images with vertical profiles. Furthermore, addition of appropriate dyes permits resists to be designed for lift-off applications with controlled retrograde profiles.

Rutter, Edward W.; Root, Jonathan C.; Bacchetti, Larry F.

1999-05-01

233

Investigation of silicon-based nanostructure morphology and chemical termination on laser desorption ionization mass spectrometry performance.  

PubMed

We have evaluated the laser desorption ionization mass spectrometry (LDI-MS) performance of six nanostructured silicon surfaces of different morphologies and chemical functionalizations. The substrates have been synthesized either by metal-assisted etching method or by vapor-liquid-solid (VLS) growth technique. In addition to the commercial nanostructured silicon-based surface (NALDI) target plates, serving as reference, the homemade surfaces have been evaluated in mass spectrometry experiments conducted with peptide solutions mimicking tryptic digests. LDI surfaces synthesized by metal-assisted etching method were the most efficient in terms of signal intensities and number of detected peptides. The surface providing the best LDI-MS performance was composed of two nanostructured layers. Interestingly, we also observed a significant influence of the type of organic coating (hydrocarbon vs fluorocarbon) on peptide ionization discrimination. PMID:23163782

Dupré, Mathieu; Enjalbal, Christine; Cantel, Sonia; Martinez, Jean; Megouda, Nacéra; Hadjersi, Toufik; Boukherroub, Rabah; Coffinier, Yannick

2012-11-30

234

Combined Chemical and Topographic Imaging at Atmospheric Pressure via Microprobe Laser Desorption/Ionization Mass Spectrometry-Atomic Force Microscopy  

SciTech Connect

The operational characteristics and imaging performance are described for a new instrument comprising an atomic force microscope (AFM) coupled with a pulsed laser and a linear ion trap mass spectrometer. The AFM operating mode is used to produce topographic surface images having nanometer-scale spatial and height resolution. Spatially resolved mass spectra of ions, produced from the same surface via microprobe-mode laser desorption/ionization at atmospheric pressure, are then used to create a 100 x 100 m chemical image. The effective spatial resolution of the image (~2 m) was constrained by the limit of detection (estimated to be 109 1010 ions) rather than by the diameter of the focused laser spot or the step size of the AFM sample stage. Thus, it is expected that improvements in imaging performance can be realized by implementation of post-ionization methods.

Bradshaw, James A [ORNL; Ovchinnikova, Olga S [ORNL; Meyer, Kent A [ORNL; Goeringer, Doug [ORNL

2009-01-01

235

High-performance liquid chromatography/high-resolution multiple stage tandem mass spectrometry using negative-ion-mode hydroxide-doped electrospray ionization for the characterization of lignin degradation products.  

PubMed

In the search for a replacement for fossil fuel and the valuable chemicals currently obtained from crude oil, lignocellulosic biomass has become a promising candidate as an alternative biorenewable source for crude oil. Hence, many research efforts focus on the extraction, degradation, and catalytic transformation of lignin, hemicellulose, and cellulose. Unfortunately, these processes result in the production of very complex mixtures. Further, while methods have been developed for the analysis of mixtures of oligosaccharides, this is not true for the complex mixtures generated upon degradation of lignin. For example, high-performance liquid chromatography/multiple stage tandem mass spectrometry (HPLC/MS(n)), a tool proven to be invaluable in the analysis of complex mixtures derived from many other biopolymers, such as proteins and DNA, has not been implemented for lignin degradation products. In this study, we have developed an HPLC separation method for lignin degradation products that is amenable to negative-ion-mode electrospray ionization (ESI doped with NaOH), the best method identified thus far for ionization of lignin-related model compounds without fragmentation. The separated and ionized compounds are then analyzed by MS(3) experiments to obtain detailed structural information while simultaneously performing high-resolution measurements to determine their elemental compositions in the two parts of a commercial linear quadrupole ion trap/Fourier-transform ion cyclotron resonance mass spectrometer. A lignin degradation product mixture was analyzed using this method, and molecular structures were proposed for some components. This methodology significantly improves the ability to analyze complex product mixtures that result from degraded lignin. PMID:22746183

Owen, Benjamin C; Haupert, Laura J; Jarrell, Tiffany M; Marcum, Christopher L; Parsell, Trenton H; Abu-Omar, Mahdi M; Bozell, Joseph J; Black, Stuart K; Kenttämaa, Hilkka I

2012-06-29

236

Single-photon multiple detachment in fullerene negative ions: absolute ionization cross sections and the role of the extra electron.  

PubMed

We have obtained experimental photo-double- and photo-triple-detachment cross sections for the fullerene negative ion using Advanced Light Source photons of 17-90 eV. The cross sections are 2 and 2.5 times larger than those for C60 and appear to be compressed and shifted in photon energy as compared to C60. Our analysis reveals that the additional electron in C60- primarily produces screening which is responsible for the modification of the spectrum. Both screening effects, the shift and the compression, can be quantitatively accounted for by a linear transformation of the energy axis. Applying the transformation allows us to map the neutral and negative ion cross sections onto each other, pointing out the close relationship of correlated few-electron dynamics in neutral and negatively charged extended systems. In contrast, dynamics of neutral and negatively charged atoms or small molecules are typically not closely related. PMID:23931363

Bilodeau, R C; Gibson, N D; Walter, C W; Esteves-Macaluso, D A; Schippers, S; Müller, A; Phaneuf, R A; Aguilar, A; Hoener, M; Rost, J M; Berrah, N

2013-07-26

237

Rapid determination of the molecular weight distribution of total cellular fatty acids using chemical ionization mass spectrometry.  

PubMed

A new method for the qualitative and quantitative determination of the molecular weight distribution of total cellular fatty acids is described. The method includes a simple extraction-saponification followed by chemical ionization-mass spectrometric analysis of the saponifiable matter. This technique requires small quantities of cell material which, combined with the rapidity and precision of the analysis, makes it attractive to the biologist interested in changes in the fatty acid composition of growing cells. As an example, an application of this method to the fatty acid determination of marine diatoms at different growth stages is presented. PMID:621436

Schwarzenbach, R P; Fisher, N S

1978-01-01

238

Bimolecular and unimolecular contributions to the disparate self-chemical ionizations of alpha-pinene and camphene isomers.  

PubMed

The contributions of molecular and fragment ions toward the disparate self-chemical ionization (SCI) of alpha-pinene and camphene isomers were investigated. A kinetic model was constructed to predict the SCI outcomes for these two C(10)H(16) isomers. A major portion of the camphene molecular ions (isolated 500 ms after the 10 ms EI event at 24 eV) unimolecularly dissociated within 200 s of the ionization event. Conversely, under similar experimental conditions, the alpha-pinene molecular ions as well as the major fragment ions of alpha-pinene and camphene showed no unimolecular dissociation. The alpha-pinene and camphene molecular ions yielded product ions through two different reaction mechanisms (direct charge-transfer {CT} and indirect proton transfer {PT}). The isolated terpene fragment ions at m/z 93 and 121 reacted with their respective neutrals to produce [M + H](+). Proton affinity (PA) bracketing experiments, PA additivity schemes, and alkene PA versus adiabatic ionization energy (IE) linear correlation indicated that the PAs of camphene and alpha-pinene were comparable ( approximately 210 +/- 2 kcal x mol(-1)). The observed [M + H](+) SCI terpene ions were mainly the products of various fragment ion reactions. PMID:17920928

Solouki, Touradj; Szulejko, Jan E

2007-09-01

239

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

240

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

2012-10-23

241

Photodetachment of negative helium ions below and above the 1s ionization threshold: A complex scaled configuration-interaction approach  

SciTech Connect

The photodetachment of the metastable He{sup -} 1s2s2p {sup 4}P{sup o} state has been calculated in two photon energy regions of interest: the first, named here as energy region I, below the double photoionization threshold He{sup +}(n=1), involving outer-shell ionization and doubly excited states of He{sup -}, and the second, named here as region II, above the He{sup -} 1s ionization threshold and below the He{sup +}(n=2) threshold, involving K-shell detachment and triply excited states of a He{sup -} ''hollow ion.'' We have implemented an ab initio three-electron configuration-interaction method in the LS-coupling scheme combined with complex scaling to obtain resonance positions and widths and the photodetachment cross sections. We have revisited region I, although widely studied before, as a test of our method. Notwithstanding some small discrepancies, our complex scaling results compare well with the previously published results and also add new understanding to some features in the cross section. Our emphasis is given to K-shell photodetachment in photon energy region II, where comparison is made with two other recent theoretical calculations that use completely different methods, and that were in dispute. We also compare with a very recent experiment for the He{sup -} K-shell photodetachment, which displays three major features; a broad nonresonant hump after the He 2s2p {sup 3}P{sup o} threshold and two other peaks. A complex scaling analysis of prominent structures in the photodetachment spectra in region II, previously claimed to be nonresonant structures, leads to a different conclusion; i.e., they are all true triply excited-state resonances, and two of them correspond to the peaks observed experimentally.

Sanz-Vicario, Jose Luis; Lindroth, Eva; Brandefelt, Nicklas [Department of Atomic Physics, Stockholms Centrum foer Fysik, Astronomi och Bioteknik (SCFAB), Fysikum, S-106 91 Stockholm (Sweden)

2002-11-01

242

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

243

Evaluation of gas chromatography-atmospheric pressure chemical ionization-mass spectrometry as an alternative to gas chromatography-electron ionization-mass spectrometry: Avocado fruit as example.  

PubMed

Although GC-APCI-MS was developed more than 40 years ago this coupling is still far from being a routine technique. One of the reasons explaining the limited use of GC-APCI so far is the lack of spectral database which facilitates the identification of the compounds under study. The first application of a very recently developed GC-APCI database to identify as many compounds as possible in a complex matrix such as avocado fruit is presented here. The results achieved by using this database has been checked against those obtained using traditional GC-EI-MS and a comparison of the MS signals observed in both ionization sources has been carried out. 100 compounds belonging to different chemical families were identified in the matrix under study. Considering the results of this study, the wide range of application (in terms of polarity and size of analytes) and the robustness of APCI as interface, the high quality of TOF spectra, and our library as a publicly available resource, GC-APCI-TOF MS is definitively a valuable addition to the "metabolomics toolbox". PMID:24054422

Hurtado-Fernández, Elena; Pacchiarotta, Tiziana; Longueira-Suárez, Enrique; Mayboroda, Oleg A; Fernández-Gutiérrez, Alberto; Carrasco-Pancorbo, Alegría

2013-08-30

244

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

245

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

NASA Astrophysics Data System (ADS)

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

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

246

Determination of 3-methyl-2,4-nonanedione in red wines using methanol chemical ionization ion trap mass spectrometry.  

PubMed

A compound associated with oxidized flavor in red wines was recently-identified as 3-methyl-2,4-nonanedione (MND). In order to quantify it, positive chemical ionization (PCI) in an ion trap was studied using conventional liquid reagents such as methanol, acetonitrile, and acetone, as well as non-conventional liquid reagents such as ethyl acetate, diethyl ether, pentane, isohexane, and heptane. Under laboratory conditions, very different response factors were obtained with MND depending on the gas. We also compared the detection limit of conventional CI with hybrid chemical ionization (HCI). Finally, this compound was quantified in red wines by liquid/liquid extraction without any derivatization steps, followed by GC/MS-CI analysis, using methanol as the reagent gas. Coelutions of compounds with the same m/z were checked using methanol-d(4). The method we developed was linear in the 10-300 ng/L range of MND concentrations, with satisfactory repeatability. The detection limit was 4.3 ng/L, over 3 times lower than the olfactory perception threshold of this compound (16 ng/L). The suitability of this method for assaying this diketone in red wine was demonstrated by the analyzing many wines from different vintages. PMID:21871629

Pons, Alexandre; Lavigne, Valérie; Darriet, Philippe; Dubourdieu, Denis

2011-08-16

247

A simplified chemical kinetic model for slightly ionized, atmospheric pressure nitrogen plasmas  

Microsoft Academic Search

Nitrogen plasmas at atmospheric pressure produced by 2.45 GHz microwaves at a power density of approximately 10 MW m-3 have a degree of ionization less than about 10-7. Nevertheless they have interesting and potentially important effects on polymer and metal surfaces exposed to them. An experimental programme is underway to identify the active species in the plasma and its afterglow.

J. Hugill; T. Saktioto

2001-01-01

248

Gas chromatography positive chemical ionization and tandem mass spectrometry for the analysis of organic high explosives  

Microsoft Academic Search

The characteristic ions or the parent ion resulting from ionization can be isolated in an ion trap and subjected to further fragmentation during a gas chromatography–tandem mass spectrometry (GC\\/MS\\/MS) experiment. This approach can improve the selectivity and sensitivity of explosive compounds over gas chromatography–mass spectrometry (GC\\/MS) by improving the differentiation of the target compounds from interfering and co-eluting compounds and

Jeannette M. Perr; Kenneth G. Furton; José R. Almirall

2005-01-01

249

Effect of polar protic and polar aprotic solvents on negative-ion electrospray ionization and chromatographic separation of small acidic molecules.  

PubMed

A comprehensive study investigated the effect of polar protic (methanol and water) and polar aprotic (acetonitrile and acetone) solvents on the chromatographic separation and negative-ion electrospray (ESI) response of 49 diverse small, acidic molecules. Flow injection experiments on a triple quadrupole were used to measure the response in neat solvents after optimization of source conditions and implementation of a rigorous quality control program (the later ensured that changes in analyte response were due to the analyte/solvent measured and not changes in instrument performance over time). In all solvents, compounds with electron-withdrawing groups and extended conjugation ionized best due to resonance and inductive effects. Ionization was greatest in methanol or water for all compounds that elicited a response, thus revealing that enhanced sensitivity and lower limits of detection are achieved with polar protic solvents. Response in acetone was equal to or slightly lower than response in acetonitrile in flow injection experiments; however, the water/acetonitrile and water/acetone mobile phases produced the better chromatographic separation. Water/methanol produced slightly less satisfactory separation but the greatest overall response. This increase in response was attributed to the protic nature of methanol and the elution of compounds in a higher organic mobile phase composition (retention times were ?30% later in methanol). This work is intended to facilitate rational liquid chromatography/mass spectrometry method development for small molecule applications, including metabolomics. PMID:23066894

Huffman, Brian A; Poltash, Michael L; Hughey, Christine A

2012-11-02

250

Chemically induced twist-bend nematic liquid crystals, liquid crystal dimers, and negative elastic constants.  

PubMed

Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition. PMID:24032852

Adlem, K; Copi?, M; Luckhurst, G R; Mertelj, A; Parri, O; Richardson, R M; Snow, B D; Timimi, B A; Tuffin, R P; Wilkes, D

2013-08-12

251

Chemically induced twist-bend nematic liquid crystals, liquid crystal dimers, and negative elastic constants  

NASA Astrophysics Data System (ADS)

Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition.

Adlem, K.; ?opi?, M.; Luckhurst, G. R.; Mertelj, A.; Parri, O.; Richardson, R. M.; Snow, B. D.; Timimi, B. A.; Tuffin, R. P.; Wilkes, D.

2013-08-01

252

Chemically amplified negative-tone resist using novel acryl polymer for 193-nm lithography  

NASA Astrophysics Data System (ADS)

We report the development of a novel acryl polymer with an (alpha) -hydroxymethyl acrylate in the application to 193nm chemically amplified negative-tone resist. This new polymer structure consists of ((alpha) -hydroxymethyl)acrylate and MAA. The ester and alcohol group in the polymer contribute to an intramolecule and/or intermolecular hybrid crosslinking reactions without crosslinker and in the presence of a photo generated acid as a catalysis. In an intramolecular crosslink reaction, the ester group reacts to a neighboring hydroxymethyl group within the polymer chain. As a result, a lactone group is made in the main polymer chain. On the other hand, in an intermolecular crosslink reaction, the ester group reacts to a hydroxymethyl group of another polymer chain to make an ester chain. In this reaction, the new polymer is densely crosslinked and fine resist pattern is obtained without having any swelling problem. Consequently, the resist is optimized and contains the new polymer, photoacid generator and a small amount of crosslinker. Under conventional illumination condition, 180nm line and space pattern are achieved without any kind of swelling problem. The sensitivity is 40 mJ/cm2 with the standard developer, NMD-3 2.38 percent.

Hada, Hideo; Iwai, Takeshi; Nakayama, Toshimasa

1999-05-01

253

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

254

Development of liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry for analysis of halogenated flame retardants in wastewater.  

PubMed

Until recently, atmospheric pressure photoionization (APPI) has typically been used for the determination of non-polar halogenated flame retardants (HFRs) by liquid chromatography (LC) tandem mass spectrometry. In this study, we demonstrated the feasibility of utilizing liquid chromatography atmospheric pressure chemical ionization (APCI) tandem mass spectrometry (LC-APCI-MS/MS) for analysis of 38 HFRs. This developed method offered three advantages: simplicity, rapidity, and high sensitivity. Compared with APPI, APCI does not require a UV lamp and a dopant reagent to assist atmospheric pressure ionization. All the isomers and the isobaric compounds were well resolved within 14-min LC separation time. Excellent instrument detection limits (6.1 pg on average with 2.0 muL injection) were observed. The APCI mechanism was also investigated. The method developed has been applied to the screening of wastewater samples for screening purpose, with concentrations determined by LC-APCI-MS/MS agreeing with data obtained via gas chromatography high resolution mass spectrometry. PMID:19957077

Zhou, Simon Ningsun; Reiner, Eric J; Marvin, Chris; Helm, Paul; Riddell, Nicole; Dorman, Frank; Misselwitz, Michelle; Shen, Li; Crozier, Patrick; Macpherson, Karen; Brindle, Ian D

2009-12-02

255

Detection of non-prescription heroin markers in urine with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

The planned introduction of a prescription heroin program in Germany created a need for differentiation between non-prescription and prescribed diamorphine use. The following substances were chosen as markers of non-prescription heroin: acetylcodeine (AC); its metabolites codeine (C) and codeine 6-glucuronide (C6G); papaverine (P); and noscapine (N). Typical heroin markers diamorphine (DAM) and its metabolites monoacetylmorphine (MAM) and morphine (M) were also determined. The drugs were extracted from urine samples with solid-phase extraction (C18) using standard 200-mg columns and 96-well microplates (100 mg). The extracts were examined with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (positive ionization) in two isocratic systems. Selected ion monitoring procedures were applied for protonated molecular masses and characteristic fragments of drugs involved. The limits of detection were in the range of 0.5-1 ng/mL urine. The occurrence of selected heroin markers was investigated in 25 urine samples collected from heroin abusers (road traffic offenders and overdosed patients). C6G was found in all samples, C in 24 samples, N in 22 samples, MAM in 16 samples, P in 14 samples, DAM in 12 samples, and AC in 4 samples. The appearance of these compounds in urine reflects their pharmacokinetic properties and the composition of non-prescription heroin. PMID:11550816

Bogusz, M J; Maier, R D; Erkens, M; Kohls, U

2001-09-01

256

Effect of relative humidity on the detection of sulfur dioxide and sulfuric acid using a chemical ionization mass spectrometer  

NASA Astrophysics Data System (ADS)

Detection of sulfur dioxide and sulfuric acid at high relative humidity was studied using a chemical ionization mass spectrometer (CIMS). The reactant ions used in the experiments are CO3-.nH2O (n=0-5), which react with SO2 to form SO5-.nH2O (n=0-2). H2SO4 reacts with the precursor ions to form HSO4- (m/z=97 amu) and H2SO4.CO3- (m/z=158 amu). We report the first use of the latter ionization scheme to detect sulfuric acid. High RH affects the detection of SO2 and H2SO4 by forming clusters with the reactant and product ions, reducing sensitivity. Increasing the temperature breaks these clusters. For SO2 at high RH, either SO5- (m/z=112 amu) or SO5-.H2O (m/z=130 amu) can be used for SO2 detection without a decrease in sensitivity. For H2SO4 at high RH, it is preferred to detect the ion H2SO4.CO3- because the background signal at 158 amu is small, and a better sensitivity can be achieved.

Salcedo, D.; Villalta, P. W.; Varutbangkul, V.; Wormhoudt, J. C.; Miake-Lye, R. C.; Worsnop, D. R.; Ballenthin, J. O.; Thorn, W. F.; Viggiano, A. A.; Miller, T. M.; Flagan, R. C.; Seinfeld, J. H.

2004-01-01

257

REDUCTION OF TOXIC AND UNDESIRABLE CHEMICAL COMPOUNDS IN FOOD BY IONIZING IRRADIATION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Possible toxic and carcinogenic chemicals such as furan, acrylamide, nitrosamines, biogenic amines, and mycotoxins (aflatoxin B1, patulin, fumonisin, etc.) can accumulate in various foods during thermal processing, preservation and storage. Recent studies have suggested that irradiation reduces leve...

258

Simultaneous determination of hair cortisol, cortisone and DHEAS with liquid chromatography-electrospray ionization-tandem mass spectrometry in negative mode.  

PubMed

The present study aimed to develop a novel method for simultaneous assay of cortisol, cortisone and dehydroepiandrosterone sulfate (DHEAS) in human hair. The method was based on liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS/MS) in negative mode. Analytes were extracted from 20-mg hair incubated in 1ml of methanol for 5 days. 100?l non-SPE supernatant of the incubation solution was utilized in LC-MS/MS analysis. The liquid chromatography separation was performed on a reversed-phase C18 column with a mobile phase of 80:20 (v:v) methanol and deionized water containing 0.1% formic acid. The use of ESI in negative mode and the use of a small volume of the incubation solution significantly improved assay sensitivity. The linear range was 5-250pg/mg for cortisol and cortisone, and 5-500pg/mg for DHEAS. The limit of detection was 2pg/mg for the three analytes in hair. The coefficients of variation for intra-day and inter-day assay were less than 10%. The method was applied to determine the three analytes mentioned above of hair samples from 103 participants. The results indicated that there was no significant effect of age and education level on the hair cortisol, cortisone and DHEAS levels. The simple treatment procedure developed in the present study may facilitate simultaneous measurement of more steroids in hair. PMID:23685429

Chen, Zheng; Li, Jifeng; Zhang, Jing; Xing, Xue; Gao, Wei; Lu, Zuhong; Deng, Huihua

2013-04-25

259

Mass spectral analysis of N-oxides of Chemical Weapons Convention related aminoethanols under electrospray ionization conditions.  

PubMed

N,N'-Dialkylaminoethanols are the hydrolyzed products or precursors of chemical warfare agents such as V-agents and nitrogen mustards, and they are prone to undergo oxidation in environmental matrices or during decontamination processes. Consequently, screening of the oxidized products of aminoethanols in aqueous samples is an important task in the verification of chemical weapons convention-related chemicals. Here we report the successful characterization of the N-oxides of N,N'-dialkylaminoethanols, alkyl diethanolamines, and triethanolamine using positive ion electrospray ionization mass spectrometry. The collision-induced dissociation (CID) spectra of the [M+H](+) and [M+Na](+) ions show diagnostic product ions that enable the unambiguous identification of the studied N-oxides, including those of isomeric compounds. The proposed fragmentation pathways are supported by high-resolution mass spectrometry data and product/precursor ion spectra. The CID spectra of [M+H](+) ions included [MH-CH(4)O(2)](+) as the key product ion, in addition to a distinctive alkene loss that allowed us to recognize the alkyl group attached to the nitrogen. The [M+Na](+) ions show characteristic product ions due to the loss of groups (R) attached to nitrogen either as a radical (R) or as a molecule [R+H or (R-H)] after hydrogen migration. PMID:21259362

Sridhar, L; Karthikraj, R; Murty, M R V S; Raju, N Prasada; Vairamani, M; Prabhakar, S

2011-02-28

260

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.

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

2010-01-01

261

Comparative analysis of different plant oils by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Different vegetable oil samples (almond, avocado, corngerm, grapeseed, linseed, olive, peanut, pumpkin seed, soybean, sunflower, walnut, wheatgerm) were analyzed using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. A gradient elution technique was applied using acetone-acetonitrile eluent systems on an ODS column (Purospher, RP-18e, 125 x 4 mm, 5 microm). Identification of triacylglycerols (TAGs) was based on the pseudomolecular ion [M+1]+ and the diacylglycerol fragments. The positional isomers of triacylglycerol were identified from the relative intensities of the [M-RCO2]+ fragments. Linear discriminant analysis (LDA) as a common multivariate mathematical-statistical calculation was successfully used to distinguish the oils based on their TAG composition. LDA showed that 97.6% of the samples were classified correctly. PMID:12462617

Jakab, Annamaria; Héberger, Károly; Forgács, Esther

2002-11-01

262

Potential of atmospheric pressure chemical ionization source in GC-QTOF MS for pesticide residue analysis.  

PubMed

The potential applications of a new atmospheric pressure source for GC-MS analysis have been investigated in this work. A list of around 100 GC-amenable pesticides, which includes organochlorine, organophosphorus and organonitrogenated compounds, has been used to evaluate their behavior in the new source. Favoring the major formation of the molecular ion in the source has been the main goal due to the wide-scope screening possibilities that this fact brings in comparison with the traditional, highly fragmented electron ionization spectra. Thus, the addition of water as modifier has been tested as a way to promote the generation of protonated molecules. Pesticides investigated have been classified into six groups according to their ionization/fragmentation behavior. Four of them are characterized by the abundant formation of the protonated molecule in the atmospheric pressure source, mostly being the base peak of the spectrum. These results show that wide-scope screening could be easily performed with this source by investigating the presence of the protonated molecule ion, MH+. The developed procedure has been applied to pesticide screening in different food samples (nectarine, orange and spinach) and it has allowed the presence of several pesticides to be confirmed such as chlorpyriphos ethyl, deltamethrin and endosulfan sulfate. The availability of a quadrupole time-of-flight instrument made it feasible to perform additional MS/MS experiments for both standards and samples to go further in the confirmation of the identity of the detected compounds. Results shown in this paper have been obtained using a prototype source which exhibits promising features that could be applied to other analytical problems apart from those illustrated in this work. PMID:20641006

Portolés, T; Sancho, J V; Hernández, F; Newton, A; Hancock, P

2010-08-01

263

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

PubMed

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

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

2013-09-19

264

FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Pulse Operation of Chemical Oxygen-Iodine Laser by Pulsed Gas Discharge with the Assistance of Spark Pre-ionization  

NASA Astrophysics Data System (ADS)

The continuous wavelength chemical oxygen-iodine laser can be turned into pulse operation mode in order to obtain high energy and high pulse power. We propose an approach to produce iodine atoms instantaneously by pulsed gas discharge with the assistance of spark pre-ionization to achieve the pulsed goal. The influence of spark pre-ionization on discharge homogeneity is discussed. Voltage-current characteristics are shown and discussed in existence of the pre-ionization capacitor and peaking capacitor. The spark pre-ionization and peaking capacitor are very helpful in obtaining a stable and homogeneous discharge. The lasing is achieved at the total pressure of 2.2-2.9kPa and single pulse energy is up to 180 mJ, the corresponding specific output energy is 1.0 J/L.

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

2009-11-01

265

Quantitative analysis of chemically amplified negative photoresist using mirror-backed infrared reflection absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Infrared spectroscopy is a powerful tool for studying chemical reactions which take place in photoresist films. It provides information about functional groups present in the material, is nondestructive to the sample, can be used to monitor reactions in real-time, and can be used as a monitor for real-time process control. Transmission spectroscopy has been used for determination of rate constants for the post exposure bake (PEB) step in both positive and negative chemically amplified x-ray resists, but in transmission the IR beam must pass through the wafer in order to reach the detector. Reflection spectroscopy is more suitable for on-line monitoring because all the optics are located on the same side of the wafer; however, traditional reflection spectra of thin films contain interference fringes which make quantitative analysis difficult. We have developed a method, called mirror-backed infrared reflection- absorption spectroscopy (MBIRRAS), that eliminates the problem of interference fringes in reflection spectra. The method is capable of providing quantitative information about the concentration of functional groups in resist films and produced a linear calibration curve for a commercial crosslinker (hexamethoxymethylmelamine) in a Novolac matrix over a 20% by weight range of concentrations. MBIRRAS was also used to monitor the height of an IR peak corresponding to formation of crosslinks in Shipley negative-tone resist SAL 605 at various processing conditions. The results of this experiment show that PEB time and temperature, prebake time and temperature, and delay between exposure and PEB, all have statistically significant effects on the extent of crosslinking during PEB. In order to explain the observed effect of prebake conditions on the amount of crosslinking during the PEB step and to define the acceptable range of prebaking conditions for resist/wafer adhesion studies, another experiment was performed to demonstrate that thermally generated crosslinking occurred during an additional prebake step without any exposure to x rays. In fact, an additional prebake for 60 seconds at 110 degree(s)C can generate the same number of crosslinks as an x- ray dose of 4 mJ/cm2, while baking for 60 minutes at 110 degree(s)C is equivalent to an x-ray dose that is greater than the resist sensitivity (42 mJ/cm2). Noticeable changes in crosslink concentration were detected at 30 seconds. This suggests that crosslinking occurs during the normal prebake step and explains the dependence of linewidth on prebake time. Finally, a correlation was demonstrated between printed linewidth and MBIRRAS peak height corresponding to crosslink formation in SAL 605. This correlation, along with the demonstrated precision of the MBIRRAS method (3 sigma

Gamsky, Chris J.; Dentinger, Paul M.; Howes, Glenn R.; Taylor, James W.

1995-06-01

266

Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Identification of Nonfermenting Gram-Negative Bacilli Isolated from Cystic Fibrosis Patients?  

PubMed Central

The identification of nonfermenting gram-negative bacilli isolated from cystic fibrosis (CF) patients is usually achieved by using phenotype-based techniques and eventually molecular tools. These techniques remain time-consuming, expensive, and technically demanding. We used a method based on matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) for the identification of these bacteria. A set of reference strains belonging to 58 species of clinically relevant nonfermenting gram-negative bacilli was used. To identify peaks discriminating between these various species, the profile of 10 isolated colonies obtained from 10 different passages was analyzed for each referenced strain. Conserved peaks with a relative intensity greater than 0.1 were retained. The spectra of 559 clinical isolates were then compared to that of each of the 58 reference strains as follows: 400 Pseudomonas aeruginosa, 54 Achromobacter xylosoxidans, 32 Stenotrophomonas maltophilia, 52 Burkholderia cepacia complex (BCC), 1 Burkholderia gladioli, 14 Ralstonia mannitolilytica, 2 Ralstonia pickettii, 1 Bordetella hinzii, 1 Inquilinus limosus, 1 Cupriavidus respiraculi, and 1 Burkholderia thailandensis. Using this database, 549 strains were correctly identified. Nine BCC strains and one R. mannnitolilytica strain were identified as belonging to the appropriate genus but not the correct species. We subsequently engineered BCC- and Ralstonia-specific databases using additional reference strains. Using these databases, correct identification for these species increased from 83 to 98% and from 94 to 100% of cases, respectively. Altogether, these data demonstrate that, in CF patients, MALDI-TOF-MS is a powerful tool for rapid identification of nonfermenting gram-negative bacilli.

Degand, Nicolas; Carbonnelle, Etienne; Dauphin, Brunhilde; Beretti, Jean-Luc; Le Bourgeois, Muriel; Sermet-Gaudelus, Isabelle; Segonds, Christine; Berche, Patrick; Nassif, Xavier; Ferroni, Agnes

2008-01-01

267

Changes in Body Chemical Composition of Rats after Spaceflight as Determined with Negatively Charged Muons.  

National Technical Information Service (NTIS)

The body chemical composition of three white rats of the ''Wistar'' line was investigated by the muonic x-ray spectroscopy technique, following three weeks in spaceflight on earth satellites ''Cosmos-605'' and ''Cosmos-690''. The chemical composition of t...

R. D. Arlt V. S. Evseev H. G. Ortlepp B. M. Sabirov H. Haupt

1978-01-01

268

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

Microsoft Academic Search

Limonene is one of the most abundant monoterpenes in the atmosphere. Limonene easily reacts with gas-phase oxidants in air such as NO3, ozone and OH. Secondary organic aerosol (SOA) is formed when low vapor pressure products condense into particles. Chemicals in SOA particles can undergo further reactions with oxidants and with solar radiation that significantly change SOA composition over the

Xiang Pan

2009-01-01

269

Differentiation of various kinds of Fructus schisandrae by surface desorption atmospheric pressure chemical ionization mass spectrometry combined with Principal Component Analysis  

Microsoft Academic Search

Various kinds of Fructus schisandrae were studied by surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS) without any sample pretreatment. The volatile components in F. schisandrae were detected in the ambient environment and the analytical time for each sample was only 30s. F. schisandrae are produced mainly in 5 different geographical regions (Elunchun, Mudanjiang, Tonghua, Tieling and Shangluo), and

Zifeng Pi; Hao Yue; Li Ma; Liying Ding; Zhiqiang Liu; Shuying Liu

2011-01-01

270

Dielectric and other physical\\/chemical changes induced by ionizing radiation in poly(ether ether ketone) (PEEK) and poly(ethersulphone) (PES) films  

Microsoft Academic Search

There has been an increasing commercial and industrial demand for advanced polymeric materials capable of being utilised in harsh environments as electrical insulation. Aromatic polymers have proved to be chemically and mechanically stable in such a situation. They have been identified for use in the presence of ionizing radiation but little information is available as to their dielectric properties under

H. M. Li; R. A. Fouracre; D. J. Tedford; H. M. Banford; M. J. Given

1994-01-01

271

Investigation of aqueous-phase photooxidation of glyoxal and methylglyoxal by aerosol chemical ionization mass spectrometry: observation of hydroxyhydroperoxide formation.  

PubMed

Aqueous-phase processing of glyoxal (GLY) and methylglyoxal (MG) produces highly oxygenated, less volatile organic acids that can contribute to SOA formation and aging. In this study, aerosol chemical ionization mass spectrometry (aerosol CIMS) is employed to monitor aqueous-phase photooxidation of GLY and MG. Using iodide (I(-)) as the reagent ion, aerosol CIMS can simultaneously detect important species involved in the reactions: organic acids, peroxides, and aldehydes, so that the reconstructed total organic carbon (TOC) concentrations from aerosol CIMS data agree well with offline TOC analysis. This study also reports the first direct detection of hydroxyhydroperoxide (HHP) formation from the reaction of H(2)O(2) with GLY or MG. The formation of HHPs is observed to be reversible and an estimate of their equilibrium constants is made to be between 40 and 200 M(-1). Results of this study suggest that HHPs can form additional formic acid and acetic acid via photooxidation and regenerate GLY or MG during photooxidation, compensating their loss. HHP formation needs to be further studied for inclusion in aqueous-phase chemical models given that it may affect the aqueous partitioning of carbonyls in the atmosphere. PMID:22296207

Zhao, R; Lee, A K Y; Abbatt, J P D

2012-03-02

272

Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH4-NH3 gas mixtures.  

PubMed

The application of a laser-induced electron impact (LIEI) ionization source in studying the gas-phase chemistry of the SiH(4)/NH(3) hot-wire chemical vapor deposition (HWCVD) system has been investigated. The LIEI source is achieved by directing an unfocused laser beam containing both 118 nm (10.5 eV) vacuum ultraviolet (VUV) and 355 nm UV radiations to the repeller plate in a time-of-flight mass spectrometer. Comparison of the LIEI source with the conventional 118 nm VUV single-photon ionization (SPI) method has demonstrated that the intensities of the chemical species with ionization potentials (IP) above 10.5 eV, e.g., H(2), N(2) and He, have been significantly enhanced with the incorporation of the LIEI source. It is found that the SPI source due to the 118 nm VUV light coexists in the LIEI source. This allows simultaneous observations of parent ions with enhanced intensity from VUV SPI and their "fingerprint" fragmentation ions from LIEI. It is, therefore, an effective tool to diagnose the gas-phase chemical species involved with both NH(3) and SiH(4) in the HWCVD reactor. In using the LIEI source to SiH(4), NH(3) and their mixtures, it has been shown that the NH(3) decomposition is suppressed with the addition of SiH(4) molecules. Examination of the NH(3) decomposition percentage and the time to reach the N(2) and H(2) steady-state intensities for various NH(3)/SiH(4) mixtures suggests that the extent of the suppression is enhanced with more SiH(4) content in the mixture. With increasing filament temperatures, the negative effect of SiH(4) becomes less important. PMID:17869128

Eustergerling, Brett; Hèden, Martin; Shi, Yujun

2007-08-24

273

Liquid chromatography/negative electrospray ionization ion trap MS(2) mass spectrometry application for the determination of microcystins occurrence in Southern Portugal water reservoirs.  

PubMed

Microcystins (MCs) are toxins produced by cyanobacteria which are common organisms in the phytoplankton of eutrophic lakes, rivers and freshwater reservoirs. In the present work, a novel method of liquid chromatography-electrospray ion trap tandem mass spectrometry (LC/ESI/Ion trap-MS/MS), operated in the negative ionization mode, was developed for the analysis of these cyanotoxins. The method was applied to determine the amounts of total microcystins-LR, -YR and -RR in two water reservoirs in Southern Portugal, namely Alqueva and Beliche. A total of 30 water samples were analysed along 2011. Solid phase extraction (SPE) was used for sample cleaning-up and analyte enrichment. The extracted toxins were separated on a C18 column with a gradient of acetonitrile/water with 0.1% formic acid. Detection of microcystins was carried out using multiple reaction monitoring (MRM) in the negative polarity mode, as this method gave a higher selectivity. The MC-RR, YR and LR quantification limits were 17.9, 31.7 and 15.8 ng/L, respectively; quite below the limits recommended by WHO guidelines for drinking water (1 ?g/L). Total MC highest concentrations were found in the warm months of June, July and September in Alqueva sampling sites, with concentrations of MC LR and RR ranging 17-344 and 25-212 ng/L, respectively, showing comparable results for MC-RR and LR and slightly lower concentration of MC-YR. Detected values for Beliche reservoir were below quantification limits. PMID:23896533

Rodrigues, M A; Reis, M P; Mateus, M C

2013-07-26

274

Desulfurization of phosphorothioate oligonucleotides via the sulfur-by-oxygen replacement induced by the hydroxyl radical during negative electrospray ionization mass spectrometry.  

PubMed

While the occurrence of desulfurization of phosphorothioate oligonucleotides in solution is well established, this study represents the first attempt to investigate the basis of the unexpected desulfurization via the net sulfur-by-oxygen (S-O) replacement during negative electrospray ionization (ESI). The current work, facilitated by quantitative mass deconvolution, demonstrates that considerable desulfurization can take place even under common negative ESI operating conditions. The extent of desulfurization is dependent on the molar phosphorothioate oligonucleotide-to-hydroxyl radical ratio, which is consistent with the corona discharge-induced origin of the hydroxyl radical leading to the S-O replacement. This hypothesis is supported by the fact that an increase of the high-performance liquid chromatography (HPLC) flow rate and the on-column concentration of a phosphorothioate oligonucleotide, as well as a decrease of the electrospray voltage reduce the degree of desulfurization. Comparative LC-tandem mass spectrometry (MS/MS) sequencing of a phosphorothioate oligonucleotide and its corresponding desulfurization product revealed evidence that the S-O replacement occurs at multiple phosphorothioate internucleotide linkage sites. In practice, the most convenient and effective strategy for minimizing this P?=?O artifact is to increase the LC flow rate and the on-column concentration of phosphorothioate oligonucleotides. Another approach to mitigate possible detrimental effects of the undesired desulfurization is to operate the ESI source at a very low electrospray voltage to diminish the corona discharge; however this will significantly compromise sensitivity when analyzing the low-level P?=?O impurities in phosphorothioate oligonucleotides. PMID:22791250

Wu, Lianming; White, David E; Ye, Connie; Vogt, Frederick G; Terfloth, Gerald J; Matsuhashi, Hayao

2012-07-01

275

CHEMICAL SELECTION OF ALCOHOL DEHYDROGENASE NEGATIVE MUTANTS IN DROSOPHILAlJ  

Microsoft Academic Search

We describe a selection procedure which utilizes the vapor from an unsaturated alcohol, 1 -pentene-3-01, for the detection and isolation of mutant flies with little or no alcohol dehydrogenase activity. ADH-negative flies are unaffected by exposure to the unsaturated alcohol, but ADH positives (wild- types) die after short exposure. The technique can be used to select rare ADH- negative individuals

WILLIAM H. SOFER; MARK A. HATKOFF

276

Screening for forensically relevant benzodiazepines in human hair by gas chromatography-negative ion chemical ionization-mass spectrometry  

Microsoft Academic Search

A procedure is presented for the detection in human hair of forensically relevant benzodiazepines, i.e. nordiazepam, oxazepem, bromazepam, diazepam, lorazepam, flunitrazepam, alprazolam and triazolam. The method involves decontamination of hair with methylene chloride, pulverization in a ball mill, incubation of 50 mg powdered hair in Soerensen buffer (pH 7.6) in the presence of prazepam-d5 used as internal standard, liquid-liquid extraction

V. Cirimele; P. Kintz; B. Ludes

1997-01-01

277

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

SciTech Connect

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

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

2005-01-01

278

Liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry method for the quantification of pregabalin in human plasma.  

PubMed

A sensitive high-performance liquid chromatography positive ion atmospheric pressure chemical ionization tandem mass spectrometry method was developed and validated for the quantification of pregabalin in human plasma. Following liquid-liquid extraction, the analyte was separated using an isocratic mobile phase on a reverse-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M+H](+) ions, m/z 160-142 for pregabalin and m/z 482-258 for the internal standard. The assay exhibited a linear dynamic range of 1-10,000ng/mL for pregabalin in human plasma. The lower limit of quantification was 1ng/mL with a relative standard deviation of less than 11.4%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 4.0min for each sample made it possible to analyze more than 300 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic studies. PMID:19837015

Nirogi, Ramakrishna; Kandikere, Vishwottam; Mudigonda, Koteshwara; Komarneni, Prashanth; Aleti, Raghupathi

2009-10-08

279

A new rapid micro-method for the molecular-chemical characterization of rhizodeposits by field-ionization mass spectrometry.  

PubMed

Time-consuming investigation of rhizodeposit composition by leaching, freeze-drying of leachate, and pyrolysis-field ionization mass spectrometry (Py-FIMS) of solid samples was replaced by direct Py-FIMS of a 5 microL liquid rhizodeposit sample which was evaporated overnight in the quartz tube of a mass spectrometer inlet system. Application of this new rapid technique to a set of 14 liquid rhizodeposit samples from maize (Zea mays L.), leached twice with a time lag of 80 min, unequivocally showed the effect of soil texture on the chemical composition of the rhizodeposits. Irrespective of leaching time, a partial least-squares analysis separated the Py-FI mass spectra of the maize rhizodeposits leached from a soil from those leached from a soil + quartz sand-mixture (prepared by addition of 50% w/w quartz sand to the original soil). The signals which had the strongest discrimination power and were significantly enriched in leachates from the soil + quartz sand were assigned to sugars, peptides and polyamines. Mass signals of putrescine and cadaverine, a priori not expected in the rhizodeposits, were indicators of modified root environment and rhizosphere processes in the soil + quartz sand. In conclusion, the new rapid mass spectrometric profiling method is suitable for rhizosphere research because it requires very small sample volumes, is fast and highly sensitive to detect and quantify a wide range of a priori expected and unexpected organic substances. PMID:18350563

Leinweber, Peter; Eckhardt, Kai-Uwe; Fischer, Holger; Kuzyakov, Yakov

2008-04-01

280

Self-aspirating atmospheric pressure chemical ionization source for direct sampling of analytes on surfaces and in liquid solutions.  

PubMed

A self-aspirating heated nebulizer probe is described and demonstrated for use in the direct analysis of analytes on surfaces and in liquid samples by atmospheric pressure chemical ionization (APCI) mass spectrometry. Functionality and performance of the probe as a self-aspirating APCI source is demonstrated using reserpine and progesterone as test compounds. The utility of the probe to sample analytes directly from surfaces was demonstrated first by scanning development lanes of a reversed-phase thin-layer chromatography plate in which a three-component dye mixture, viz., Fat Red 7B, Solvent Green 3, and Solvent Blue 35, was spotted and the components were separated. Development lanes were scanned by the sampling probe operated under computer control (x, y plane) while full-scan mass spectra were recorded using a quadrupole ion trap mass spectrometer. In addition, the ability to sample the surface of pharmaceutical tablets (viz., Extra Strength Tylenol and Evista tablets) and to detect the active ingredients (acetaminophen and raloxifene, respectively) selectively was demonstrated using tandem mass spectrometry (MS/MS). Finally, the capability to sample analyte solutions from the wells of a 384-well microtiter plate and to perform quantitative analyses using MS/MS detection was illustrated with cotinine standards spiked with cotinine-d3 as an internal standard. PMID:16021617

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

2005-01-01

281

Photodegradation of secondary organic aerosol generated from limonene oxidation by ozone studied with chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Photodegradation of secondary organic aerosol (SOA) prepared by ozone-initiated oxidation of D-limonene is studied with an action spectroscopy approach, which relies on detection of volatile photoproducts with chemical ionization mass-spectrometry as a function of the UV irradiation wavelength. Efficient photodegradation is observed for a broad range of ozone (0.1-300 ppm) and D-limonene (0.02-3 ppm) concentrations used in the preparation of SOA. The observed photoproducts are dominated by oxygenated C1-C3 compounds such as methanol, formic acid, acetaldehyde, acetic acid, and acetone. The irradiation wavelength dependence of the combined yield of the photoproducts closely tracks the absorption spectrum of the SOA material suggesting that photodegradation is not limited to the UV wavelengths. Kinetic simulations suggest that RO2+HO2/RO2 reactions represent the dominant route to photochemically active carbonyl and peroxide species in the limonene SOA prepared in these experiments. Similar photodegradation processes are likely to occur in realistic SOA produced by OH- or O3-initiated oxidation of biogenic volatile organic compounds in clean air.

Pan, X.; Underwood, J. S.; Xing, J.-H.; Mang, S. A.; Nizkorodov, S. A.

2009-06-01

282

Photodegradation of secondary organic aerosol generated from limonene oxidation by ozone studied with chemical ionization mass spectrometry  

NASA Astrophysics Data System (ADS)

Photodegradation of secondary organic aerosol (SOA) prepared by ozone-initiated oxidation of D-limonene is studied with an action spectroscopy approach, which relies on detection of volatile photoproducts with chemical ionization mass-spectrometry as a function of the UV irradiation wavelength. Efficient photodegradation is observed for a broad range of ozone and D-limonene concentrations (0.1-300 ppm) used in the preparation of SOA. The observed photoproducts are dominated by oxygenated C1-C3 compounds such as methanol, formic acid, acetaldehyde, acetic acid, and acetone. The irradiation wavelength dependence of the combined yield of the photoproducts closely tracks the absorption spectrum of the SOA material suggesting that photodegradation is not limited to the UV wavelengths. Kinetic simulations suggest that RO2+HO2/RO2 reactions represent the dominant route to photochemically active carbonyl and peroxide species in the limonene SOA material. Similar photodegradation processes are likely to occur in realistic SOA produced by OH- or O3-initiated oxidation of biogenic volatile organic compounds in clean air.

Pan, X.; Underwood, J. S.; Xing, J.-H.; Mang, S. A.; Nizkorodov, S. A.

2009-02-01

283

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 50min, 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 (40min) 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 10ng/g level. PMID:23992841

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

2013-08-16

284

A simplified chromatin dispersion (nuclear halo) assay for detecting DNA breakage induced by ionizing radiation and chemical agents.  

PubMed

Methods for visualizing DNA damage at the microscopic level are based on treatment of cell nuclei with saline or alkaline solutions. These procedures for achieving chromatin dispersion produce halos that surround the nuclear remnants. We improved the fast halo assay for visualizing DNA breakage in cultured cells to create a simplified method for detection and quantitative evaluation of DNA breakage. Nucleated erythrocytes from chicken blood were selected as a model test system to analyze the production of nuclear halos after treatment with X-rays or H(2)O(2). After staining with ethidium bromide or Wright's methylene blue-eosin solution, nuclear halos were easily observed by fluorescence or bright-field microscopy, respectively, which permits rapid visualization of DNA breakage in damaged cells. By using image processing and analysis with the public domain ImageJ software, X-ray dose and H(2)O(2) concentration could be correlated well with the size of nuclear halos and the halo:nucleus ratio. Our results indicate that this simplified nuclear halo assay can be used as a rapid, reliable and inexpensive procedure to detect and quantify DNA breakage induced by ionizing radiation and chemical agents. A mechanistic model to explain the differences between the formation of saline or alkaline halos also is suggested. PMID:21916782

Galaz-Leiva, S; Pérez-Rodríguez, G; Blázquez-Castro, A; Stockert, J C

2011-09-15

285

Simultaneous determination of cyanide and thiocyanate in plasma by chemical ionization gas chromatography mass-spectrometry (CI-GC-MS).  

PubMed

An analytical method utilizing chemical ionization gas chromatography-mass spectrometry was developed for the simultaneous determination of cyanide and thiocyanate in plasma. Sample preparation for this analysis required essentially one-step by combining the reaction of cyanide and thiocyanate with pentafluorobenzyl bromide and simultaneous extraction of the product into ethyl acetate facilitated by a phase-transfer catalyst, tetrabutylammonium sulfate. The limits of detection for cyanide and thiocyanate were 1 ?M and 50 nM, respectively. The linear dynamic range was from 10 ?M to 20 mM for cyanide and from 500 nM to 200 ?M for thiocyanate with correlation coefficients higher than 0.999 for both cyanide and thiocyanate. The precision, as measured by %RSD, was below 9 %, and the accuracy was within 15 % of the nominal concentration for all quality control standards analyzed. The gross recoveries of cyanide and thiocyanate from plasma were over 90 %. Using this method, the toxicokinetic behavior of cyanide and thiocyanate in swine plasma was assessed following cyanide exposure. PMID:22941221

Bhandari, Raj K; Oda, Robert P; Youso, Stephanie L; Petrikovics, Ilona; Bebarta, Vikhyat S; Rockwood, Gary A; Logue, Brian A

2012-09-04

286

An aircraft-borne chemical ionization - ion trap mass spectrometer (CI-ITMS) for fast PAN and PPN measurements  

NASA Astrophysics Data System (ADS)

An airborne chemical ionization ion trap mass spectrometer instrument (CI-ITMS) has been developed for tropospheric and stratospheric fast in-situ measurements of PAN (peroxyacetyl nitrate) and PPN (peroxypropionyl nitrate). The first scientific deployment of the FASTPEX instrument (FASTPEX = Fast Measurement of Peroxyacyl nitrates) took place in the Arctic during 18 missions aboard the DLR research aircraft Falcon, within the framework of the POLARCAT-GRACE campaign in the summer of 2008. The FASTPEX instrument is described and characteristic properties of the employed ion trap mass spectrometer are discussed. Atmospheric data obtained at altitudes of up to ~12 km are presented, from the boundary layer to the lowermost stratosphere. Data were sampled with a time resolution of 2 s and a 2? detection limit of 25 pmol mol-1. An isotopically labelled standard was used for a permanent on-line calibration. For this reason the accuracy of the PAN measurements is better than ±10% for mixing ratios greater than 200 pmol mol-1. PAN mixing ratios in the summer Arctic troposphere were in the order of a few hundred pmol mol-1 and generally correlated well with CO. In the Arctic boundary layer and lowermost stratosphere smaller PAN mixing ratios were observed due to a combination of missing local sources of PAN precursor gases and efficient removal processes (thermolysis/photolysis). PPN, the second most abundant PAN homologue, was measured simultaneously. Observed PPN/PAN ratios range between ~0.03 and 0.3.

Roiger, A.; Aufmhoff, H.; Stock, P.; Arnold, F.; Schlager, H.

2011-02-01

287

An aircraft-borne chemical ionization - ion trap mass spectrometer (CI-ITMS) for fast PAN and PPN measurements  

NASA Astrophysics Data System (ADS)

An airborne chemical ionization ion trap mass spectrometer instrument (CI-ITMS) has been developed for tropospheric and stratospheric fast in-situ measurements of PAN (peroxyacetyl nitrate) and PPN (peroxypropionyl nitrate). The first scientific deployment of the FASTPEX instrument (FASTPEX = Fast Measurement of Peroxyacyl nitrates) took place in the Arctic during 18 missions aboard the DLR research aircraft Falcon, within the framework of the POLARCAT-GRACE campaign in the summer of 2008. The FASTPEX instrument is described and characteristic properties of the employed ion trap mass spectrometer are discussed. Atmospheric data obtained at altitudes of up to ~12 km are presented, from the boundary layer to the lowermost stratosphere. Data were sampled with a time resolution of 2 s and a 2? detection limit of 25 pmol mol-1. An isotopically labelled standard was used for a permanent online calibration. For this reason the accuracy of the PAN measurements is better than ±10% for mixing ratios greater than 200 pmol mol-1. PAN mixing ratios in the summer Arctic troposphere were in the order of a few hundred pmol mol-1 and generally correlated well with CO. In the Arctic boundary layer and lowermost stratosphere smaller PAN mixing ratios were observed due to a combination of missing local sources of PAN precursor gases and efficient removal processes (thermolysis/photolysis). PPN, the second most abundant PAN homologue, was measured simultanously. Observed PPN/PAN ratios range between ~0.03 and 0.3.

Roiger, A.; Aufmhoff, H.; Stock, P.; Arnold, F.; Schlager, H.

2010-10-01

288

Eddy Correlation Measurements of the Air/Sea Flux of DMS Using Atmospheric Pressure Chemical Ionization Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The physical and chemical processes controlling gas exchange across the air/sea interface are not well understood. Many laboratory and field studies of the physical controls on gas exchange have been performed using indirect mass balance measurement techniques, but there have been few direct gas flux measurements over the ocean. Eddy correlation is a micrometeorological technique, which can measure fluxes directly. The use of this technique for trace gas flux measurements has been limited in part due to the lack of sufficiently sensitive, fast-response gas detectors. Atmospheric pressure chemical ionization mass spectrometry (API/CIMS) is a highly sensitive, fast response detection method. We carried out a field study at the Scripps Institute of Oceanography pier to test the use of API/CIMS for eddy correlation flux measurements of dimethylsulfide (DMS). Cospectra of vertical winds and DMS demonstrate that flux from the sea surface was routinely detected. The API/CIMS detected atmospheric fluctuations less than 0.5 Hz. This frequency cut-off probably reflects attenuation in the inlet tubing rather than in the detector itself. The partial pressure of DMS in surface seawater was also determined using the API/CIMS, after equilibration with N2 in a continuous flow membrane equilibrator. Gas exchange coefficients were computed from the flux and air/sea concentration gradient. Gas transfer coefficients determined in this study ranged from 0.66 cm/hr to 38.43 cm/hr, for mean horizontal wind speeds ranging from 1 to 6 m/s. The gas transfer coefficients are positively correlated with wind speed, but are significantly greater than current estimates of gas transfer coefficients at similar wind speeds over the ocean. These elevated gas transfer coefficients probably reflect enhanced water-side turbulence induced by the interaction of wave motion with the shallow bottom at this site.

Marandino, C. A.; Debruyn, W. J.; Saltzman, E. S.

2003-12-01

289

Analysis of gaseous toxic industrial compounds and chemical warfare agent simulants by atmospheric pressure ionization mass spectrometry.  

PubMed

The suitability of atmospheric pressure chemical ionization mass spectrometry as sensing instrumentation for the real-time monitoring of low levels of toxic compounds is assessed, especially with respect to public safety applications. Gaseous samples of nine toxic industrial compounds, NH3, H2S, Cl2, CS2, SO2, C2H4O, HBr, C6H6 and AsH3, and two chemical warfare agent simulants, dimethyl methylphosphonate (DMMP) and methyl salicylate (MeS), were studied. API-MS proves highly suited to this application, with speedy analysis times (<30 seconds), high sensitivity, high selectivity towards analytes, good precision, dynamic range and accuracy. Tandem MS methods were implemented in selected cases for improved selectivity, sensitivity, and limits of detection. Limits of detection in the parts-per-billion and parts-per-trillion range were achieved for this set of analytes. In all cases detection limits were well below the compounds' permissible exposure limits (PELs), even in the presence of added complex mixtures of alkanes. Linear responses, up to several orders of magnitude, were obtained over the concentration ranges studied (sub-ppb to ppm), with relative standard deviations less than 3%, regardless of the presence of alkane interferents. Receiver operating characteristic (ROC) curves are presented to show the performance trade-off between sensitivity, probability of correct detection, and false positive rate. A dynamic sample preparation system for the production of gas phase analyte concentrations ranging from 100 pptr to 100 ppm and capable of admixing gaseous matrix compounds and control of relative humidity and temperature is also described. PMID:16568176

Cotte-Rodríguez, Ismael; Justes, Dina R; Nanita, Sergio C; Noll, Robert J; Mulligan, Christopher C; Sanders, Nathaniel L; Cooks, R Graham

2006-01-18

290

Negative chemical amplification resist systems based on polyhydroxystyrenes and N-substituted imides or aldehydes  

NASA Astrophysics Data System (ADS)

Aqueous base developable negative deep UV resist systems composed of phenolic resins, monofunctional latent electrophiles, and a sulfonium salt photochemical acid generator are described. This study was carried out to see whether attachment of a bulky substituent onto the phenolic group via C- or O-alkylation reduces the dissolution rate of the phenolic resin in aqueous base to provide negative images even when no crosslinking is involved in the mechanism. The latent electrophiles selected are N-hydroxymethyl and N-aceotxymethylimides as well as high- boiling aldehydes. Our matrix resins are para-, meta-, and ortho-isomers of polyvinylphenol and copolymers of p-hydroxystyrene.

Ito, Hiroshi; Schildknegt, Klaas; Mash, Eugene A.

1991-06-01

291

Chemical ionization by [NO]+ and subsequent collision-induced dissociation for the selective on-line detection of monoterpenes and linalool.  

PubMed

Existing on-line Chemical Ionization Mass Spectrometry (CIMS) techniques for quantification of atmospheric trace gases, such as Biogenic Volatile Organic Compounds (BVOCs), suffer from difficulty in discriminating between isomeric (and more generally isobaric) compounds. Selective detection of these compounds, however, is important because they can affect atmospheric chemistry in different ways, depending on their chemical structure. In this work, Flowing Afterglow Tandem Mass Spectrometry (FATMS) was used to investigate the feasibility of the selective detection of a series of monoterpenes, an oxygenated monoterpene (linalool) and a sesquiterpene (?-caryophyllene). Ions at m/z 137 from [H(3)O](+) chemical ionization of ?-pinene, linalool and ?-caryophyllene have been subjected to Collision-Induced Dissociation (CID) with Ar in the collision cell of a tandem mass spectrometer at center-of-mass energies ranging between 0 and 8 eV. Similar fragmentation patterns were obtained, demonstrating that this method is not suited for the selective detection of these compounds. However, CID of the ions at m/z 136 produced via [NO](+) chemical ionization of a series of monoterpenes has revealed promising results. Some tracer-product ions for individual compounds or groups of compounds were found, which can be considered as a step forward towards selective on-line monitoring of BVOCs with CIMS techniques. PMID:21294204

Rimetz-Planchon, Juliette; Dhooghe, Frederik; Schoon, Niels; Vanhaecke, Frank; Amelynck, Crist

2011-03-15

292

Simple Chemical Procedure for Extending the Conductive State of Polypyrrole to More Negative Potentials.  

National Technical Information Service (NTIS)

The electronically conductive polymer polypyrrole is an electronic conductor at potentials positive of ca. -0.4 V vs. the saturated calomel electrode (SCE) and an electronic insulator at potentials negative of this value. As a result of this potential-dep...

L. S. Van Dyke S. Kuwabata C. R. Martin

1993-01-01

293

A thermal dissociation–chemical ionization mass spectrometry (TD-CIMS) technique for the simultaneous measurement of peroxyacyl nitrates and dinitrogen pentoxide  

Microsoft Academic Search

We have developed a thermal dissociation–chemical ionization mass spectrometry (TD-CIMS) technique for fast measurements of a series of peroxyacyl nitrates and dinitrogen pentoxide. Thermally generated acylperoxy radicals react with I? to produce a carboxylate ion that is unique for each parent species. NO3 resulting from the decomposition of N2O5 reacts with I? to form NO3?. The measurement technique was verified

Darlene L. Slusher; L. Gregory Huey; David J. Tanner; Frank M. Flocke; James M. Roberts

2004-01-01

294

Determination of morphine and its 3- and 6-glucuronides, codeine, codeine-glucuronide and 6-monoacetylmorphine in body fluids by liquid chromatography atmospheric pressure chemical ionization mass spectrometry  

Microsoft Academic Search

A selective assay of morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G), morphine, codeine, codeine-6-glucuronide (C6G) and 6-monoacetylmorphine (6-MAM) based on liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC–APCI–MS) is described. The drugs were extracted from serum, autopsy blood, urine, cerebrospinal fluid or vitreous humor using C18 solid-phase extraction cartridges and subjected to LC–APCI–MS analysis. The separation was performed on an ODS column

Maciej J Bogusz; Rolf-Dieter Maier; Manfred Erkens; Sarah Driessen

1997-01-01

295

Simultaneous quantification of jasmonic acid and salicylic acid in plants by vapor-phase extraction and gas chromatography-chemical ionization-mass spectrometry  

Microsoft Academic Search

Jasmonic acid and salicylic acid represent important signaling compounds in plant defensive responses against other organisms. Here, we present a new method for the easy, sensitive, and reproducible quantification of both compounds by vapor-phase extraction and gas chromatography-positive ion chemical ionization-mass spectrometry. The method is based on a one-step extraction, phase partitioning, methylation with HCl\\/methanol, and collection of methylated and,

Juergen Engelberth; Eric A Schmelz; Hans T Alborn; Yasmin J Cardoza; Juan Huang; James H Tumlinson

2003-01-01

296

Technical Note: Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds  

Microsoft Academic Search

The performance of a new chemical ionization re- action time-of-flight mass spectrometer (CIR-TOF-MS) util- ising the environment chamber SAPHIR (Simulation of At- mospheric Photochemistry In a large Reaction Chamber- Forschungzentrum Julich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composi- tion and Change the European NeTwork for excellence) sup- ported oxygenated volatile organic compound (OVOC)

K. P. Wyche; R. S. Blake; A. M. Ellis; P. S. Monks; T. Brauers; R. Koppmann; E. C. Apel

2007-01-01

297

Technical Note: Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds  

Microsoft Academic Search

The performance of a new chemical ionization reaction time-of-flight mass spectrometer (CIR-TOF-MS) utilising the environment chamber SAPHIR (Simulation of Atmospheric Photochemistry In a large Reaction Chamber- Forschungzentrum Jülich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composition and Change the European NeTwork for excellence) supported oxygenated volatile organic compound (OVOC) measurement intercomparison during January 2005.

K. P. Wyche; R. S. Blake; A. M. Ellis; P. S. Monks; T. Brauers; R. Koppmann; E. C. Apel

2007-01-01

298

Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds  

Microsoft Academic Search

The performance of a new chemical ionization reaction time-of-flight mass spectrometer (CIR-TOF-MS) utilising the environment chamber SAPHIR (Simulation of Atmospheric Photochemistry In a large Reaction Chamber - Forschungzentrum Jülich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composition and Change the European NeTwork for excellence) supported oxygenated volatile organic compound (OVOC) measurement intercomparison during January

K. P. Wyche; R. S. Blake; A. M. Ellis; P. S. Monks; T. Brauers; R. Koppmann; E. Apel

2006-01-01

299

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

Microsoft Academic Search

A reliable, sensitive and eco-friendly injection-port trimethylsilylated (TMS) derivatization and gas chromatography–tandem mass spectrometry (GC–MS\\/MS) with furan chemical ionization (furan-CI) method was developed to determine melamine and cyanuric acid in powdered milk samples. The effects of several parameters related to the TMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) and of various CI agents were investigated.

Shin-Hwa Tzing; Wang-Hsien Ding

2010-01-01

300

Particulate Organic Matter Detection Using a Micro-Orifice Volatilization Impactor Coupled to a Chemical Ionization Mass Spectrometer (MOVI-CIMS)  

Microsoft Academic Search

We describe a new method, Micro-Orifice Volatilization Impactor-CIMS (MOVI-CIMS) that couples two well-proven techniques, inertial impaction and chemical ionization mass spectrometry (CIMS). This technique allows both gas and condensed-phase composition data to be obtained on a semi-continuous basis. Gas-phase compounds are analyzed while particles are collected on a post. This collection step is followed by thermal desorption in an inert

Reddy L. N. Yatavelli; Joel A. Thornton

2010-01-01

301

Screening, library-assisted identification and validated quantification of oral antidiabetics of the sulfonylurea-type in plasma by atmospheric pressure chemical ionization liquid chromatography–mass spectrometry  

Microsoft Academic Search

An atmospheric pressure chemical ionization liquid chromatographic–mass spectrometric (APCI–LC–MS) LC–MS assay is presented for fast and reliable screening and identification as well as precise and sensitive quantification of oral antidiabetics of the sulfonylurea-type (OADs) in plasma. It allowed the specific diagnosis of an overdose situation or a Munchausen syndrome caused by ingestion of OADs. After liquid–liquid extraction, the OADs glibenclamide,

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

2002-01-01

302

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

Microsoft Academic Search

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

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

2000-01-01

303

Composite Chemical Sensors Based on Carbon-Filled Patterned Negative Resists  

NASA Astrophysics Data System (ADS)

Conductometric chemical sensors based on polymer composite films, synthesized by adding conductive fillers to the polymer solutions and deposited between two predefined electrodes, are well established. Deposition of the sensitive composites is usually applied to sensor devices by solvent casting methods such as spin coating, spray coating and drop casting. These methods lack in pattern precision and repeatability. In order to overcome pertinent problems the application of conventional patterning methods for the fabrication of the conductive sensing array is proposed. In this work, we present the deposition of two conductive polymer composites poly(dimethylsiloxane)/carbon black and epoxy polymer/carbon black on the same substrate. Each polymer composite is deposited onto two respective electrodes, effectively creating a conductive polymer chemical sensor pair. The two sensors performance is evaluated and considered as a first step towards the fabrication of a conductometric polymer composite array. Electrical vs dimensional sensitivity issues and the significance of electrode configuration are considered.

Chatzandroulis, Stavros; Andreadis, Nikolaos; Goustouridis, Dimitrios; Quercia, Luigi; Raptis, Ioannis; Beltsios, Konstantinos

2007-09-01

304

Perceived relation between odors and a negative event determines learning of symptoms in response to chemicals  

Microsoft Academic Search

BackgroundWe investigated the effects of worrying information about chemical pollution on subjective symptoms in response to an odor that was previously associated with symptom episodes.MethodsAmmonia and butyric acid in harmless concentrations were used as odor cues, and 10% CO 2-enriched air was used to induce symptoms. One of two odors was consistently mixed with CO 2-enriched air while the other

Stephan Devriese; Winnie Winters; Ilse Van Diest; Steven De Peuter; Gerrit Vos; Karel Van de Woestijne; Omer Van den Bergh

2004-01-01

305

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

2010-07-21

306

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

307

Determination of (-)-threo-chlorocitric acid in human plasma by gas chromatography-positive chemical-ionization mass spectrometry.  

PubMed

A method is described for measuring (-)-threo-chlorocitric acid in human plasma. Plasma is acidified to pH 1 to minimize lactonization and a 13C analogue of (-)-threo-chlorocitric acid is added as internal standard. The acidified plasma is then extracted with ethyl acetate containing 10% methanol. The ethyl acetate-methanol extract is back-extracted with acetate buffer (pH 5). This extract, following adjustment to pH 1, is reextracted with ethyl acetate. The residue after removal of the ethyl acetate is treated with ethereal diazomethane. The wet residue is reconstituted in ethyl acetate and a portion of this solution is analyzed by gas chromatography-chemical ionization mass spectrometry. The mass spectrometer is set to monitor m/z 269 [MH+ of trimethylated (-)-threo-chlorocitric acid] and m/z 270 [MH+ of trimethylated (-)-threo-[13C]chlorocitric acid] in the gas chromatographic effluent. The m/z 269 to m/z 270 ion ratio in a sample containing an unknown amount of (-)-threo-chlorocitric acid is converted to an amount of compound using a calibration curve. The calibration curve is generated by analyzing control plasma spiked with various known amounts of (-)-threo-chlorocitric acid and a fixed amount of (-)-threo-[13C]chlorocitric acid. The limit of quantitation is 0.1-0.6 micrograms ml-1, depending on the characteristics of the calibration curve generated with each set of samples. The precision (relative standard deviation) at a concentration of 2 micrograms ml-1 is 3.3%. PMID:7161329

Rubio, F; De Grazia, F; Miwa, B J; Garland, W A

1982-12-10

308

Acetonitrile covalent adduct chemical ionization tandem mass spectrometry of non-methylene-interrupted pentaene fatty acid methyl esters.  

PubMed

Acetonitrile covalent adduct chemical ionization tandem mass spectrometry (CACIMS/MS) has shown to be an efficient method for the identification of double-bond position in homoallylic, conjugated and several polyene non-methylene-interrupted (NMI) fatty acid methyl esters. However, it has not been thoroughly evaluated for NMI highly unsaturated fatty acids (HUFA) with more than four double bonds. Docosahexaenoic acid (DHA)-rich single cell oil (DHASCO(®); Martek Biosciences, Corp.) was partially hydrogenated (partially hydrogenated DHASCO; PHDO) producing ten novel 22:5 and 22:6 HUFA isomers. In single-stage MS, the ratio of [M+54](+)/[M+54-32](+) for the 22:5 and 22:6 isomers indicated the presence of homoallylic or partially conjugated double-bond systems. The CACIMS/MS spectra revealed six 22:5 isomers with diagnostic ions corresponding to the homoallylic 22:5n-6 and 22:5n-3 isomers, and four distinct NMI 22:5 isomers. Diagnostic ions for four 22:6 isomers were identical to the native DHA illustrating that CACIMS/MS is sensitive to double-bond position but not geometry. Three gas chromatography (GC) peaks for partially conjugated 22:6 isomers were also detected and clearly distinguishable from homoallylic 22:6 isomers, but their CACIMS/MS spectra did not yield prominent ions indicative of double-bond position, possibly due to co-elution. Overall, CACIMS/MS was effective for determining double-bond position in NMI 22:5 isomers. Further investigations are warranted to evaluate and determine fragmentation patterns for partially conjugated and NMI 22:6 HUFA. PMID:21698676

Alves, Susana P; Tyburczy, Cynthia; Lawrence, Peter; Bessa, Rui J B; Brenna, J Thomas

2011-07-30

309

Characterization of a thermal decomposition chemical ionization mass spectrometer for the measurement of peroxy acyl nitrates (PANs) in the atmosphere  

NASA Astrophysics Data System (ADS)

This paper presents a detailed laboratory characterization of a thermal dissociation chemical ionization mass spectrometer (TD-CIMS) for the atmospheric measurement of Peroxyacetyl nitrate (PAN) and its homologues (PANs). PANs are efficiently dissociated in a heated inlet and the resulting peroxy acyl radicals are reacted with I- ions in a flow tube. The mass spectrometer detects the corresponding carboxylate ions. PAN, peroxypropionyl nitrate (PPN), peroxyisobutyryl nitrate (PiBN), peroxy-n-butyryl nitrate (PnBN), peroxyacryloyl nitrate (APAN), peroxycrotonyl nitrates (CPAN) and peroxymethacryloyl nitrate (MPAN) were cross-calibrated with both a dual channel GC/ECD and a total odd-nitrogen (NOy) instrument for the NCAR TD-CIMS' typical aircraft operation conditions. In addition, the instrument sensitivity to a number of more exotic PANs (peroxyhydroxyacetyl nitrate, methoxyformyl peroxynitrate, and peroxybenzoyl nitrate) was evaluated qualitatively by comparisons with a long-path FTIR instrument. The sensitivity for PPN is slightly higher than that of PAN. Larger aliphatic and olefinic PAN compounds generally showed lower sensitivities. We postulate that these differences are owing to secondary reactions in the thermal decomposition region, which either reduce the yield of peroxy acyl radicals or cause losses of these radicals through intramolecular decomposition. The relative importance of these secondary reactions varies considerably between different PAN species. Results also indicate that the reaction of the larger peroxy acyl radicals with the ion-water cluster, I-(H2O)n proceeds about an order of magnitude faster than with I- alone, as has been observed for peroxy acetyl radicals. Sensitivity variations among the individual PAN species at very low water vapor were observed. The results call for careful evaluation of each PAN species to be measured and for each desired operating condition of a TD-CIMS instrument.

Zheng, W.; Flocke, F. M.; Tyndall, G. S.; Swanson, A.; Orlando, J. J.; Roberts, J. M.; Huey, L. G.; Tanner, D. J.

2011-07-01

310

The fractional ionization in dark molecular clouds  

Microsoft Academic Search

Aims:We have studied the mechanisms which govern the degree of ionization of the gas in molecular clouds and prestellar cores, with a view to interpreting the relative abundances of the carbon-chain species C{ n}H and their negative ions, C{n}H^-. Methods: We followed the chemical evolution of a medium comprising gas and dust as it evolves towards its steady-state composition. Various

D. R. Flower; G. Pineau Des Forêts; C. M. Walmsley

2007-01-01

311

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

PubMed

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

Reth, Margot; Oehme, Michael

2004-03-03

312

Mass Spectral Investigations on Toxins. 7. Detection and Accurate Quantitation of Picogram Quantities of Macrocyclic Trichothecenes in Brazilian Plant Samples by Direct Chemical Ionization-Mass Spectrometer/Mass Spectrometer Techniques.  

National Technical Information Service (NTIS)

Roridins and baccharinoids are macrocyclic trichothecenes. They formed (M+NH4)(+) adducts effectively with ammonia under chemical ionization conditions. The daughter spectra of these adducts were characteristic of the macrocyclic ester bridges and indicat...

T. Krishnamurthy E. W. Sarver

1987-01-01

313

Interplay of negative pressure and hydrogen chemical effects in CeRhSn from first principles  

NASA Astrophysics Data System (ADS)

Investigations within the local spin density functional theory (LSDF) of the intermetallic hydride system CeRhSnHx were carried out for discrete model compositions in the range 0.33 ?xH ? 1.33 with the purpose of assessing the change of the cerium valence state in the neighborhood of the experimental hydride composition, CeRhSnH0.8. In agreement with experiment, the analyses of the electronic and magnetic structures and of the chemical bonding properties point to trivalent cerium for 1 ?xH ? 1.33. In contrast, for lower hydrogen amounts the hydride system stays in an intermediate-valent state for cerium, like in CeRhSn. The influence of the insertion of hydrogen is addressed from both the volume expansion and chemical bonding effects. The latter are found to have the main influence on the change of Ce valence character. Spin polarized calculations point to a finite magnetic moment carried by the Ce 4f states; its magnitude increases with xH in the range 1 ?xH ? 1.33.

Al Alam, A. F.; Matar, S. F.; Ouaini, N.; Nakhl, M.

2008-10-01

314

Quantitative analysis of cortisol and 6?-hydroxycortisol in urine by fully automated SPE and ultra-performance LC coupled with electrospray and atmospheric pressure chemical ionization (ESCi)-TOF-MS.  

PubMed

An ultra-performance LC TOF MS method for quantitative analysis of cortisol and 6?-hydroxycortisol in urine was developed. The method was used for determination of the ratio between 6?-hydroxycortisol and cortisol in urine received from autopsy cases and living persons as a measure of cytochrome P450 3A enzyme activity. Urine samples (0.25 mL) were extracted with an in-house developed fully automated 96-well SPE system. The compounds were quantified using a Waters ACQUITY UPLC system coupled to a Waters SYNAPT G2. The MS sensitivity was optimized by using negative ionization in sensitivity mode (resolution >10 000 full-width at half-maximum), and further optimized by using the enhanced duty cycle around the 410 m/z. ESCi (simultaneous electrospray and atmospheric pressure chemical ionization) mode was used to compensate for the matrix effects of postmortem urine. Finally, the SYNAPT G2 was tested as a quantitative instrument. The developed method has a measurement range from 2.5-300 ng/mL for cortisol to 10-1200 ng/mL for 6?-hydroxycortisol. Mean overall process efficiencies were 29.4 and 23.0% for cortisol and 6?-hydroxycortisol, respectively. In 20 forensic reference cases, the range of the 6?-hydroxycortisol/cortisol ratio was 0.29-14.2 with a median of 3.04. PMID:23255186

Lang, Lotte M; Dalsgaard, Petur W; Linnet, Kristian

2012-12-15

315

Low-temperature plasma ionization ion mobility spectrometry.  

PubMed

In this research work, the capability of low-temperature plasma (LTP) as an ionization source for ion mobility spectrometry (IMS) has been investigated for the first time. This new ionization source enhances the potential of IMS as a portable analytical tool and allows direct analysis of various chemical compounds without having to evaporate the analyte or seek a solvent or reagent whatsoever. The effects of parameters such as the flow rate of the discharge gas, plasma voltage, and positioning of the LTP on the IMS signal were investigated. The positive reactant ions generated by the LTP ionization source were similar to those created in a corona discharge ionization source, where the proton clusters ((H(2)O)(n)H(+)) are the most abundant reactant ion, and in the negative mode, in addition to a saturated electron peak, several negative reactant ions (e.g., NO(x)(-)) were observed too. These reactant ions subsequently ionized the gaseous samples directly and liquids or solids after evaporation by plasma desorption. The ion mobility spectra of a few selected compounds, including explosives, drugs, and amines, were obtained to evaluate the new ionization source in positive and negative modes, and the reduced mobility values (K(0)) of the originated ions were calculated. Furthermore, the method has also been applied to obtain the figures of merit for acetaminophen as a test compound. The results obtained are promising enough to ensure the use of LTP as a desorption/ionization source in IMS for analytical applications. PMID:21192661

Jafari, Mohammad T

2010-12-30

316

Double bond localization in minor homoallylic fatty acid methyl esters using acetonitrile chemical ionization tandem mass spectrometry.  

PubMed

Double bond position in natural fatty acids is critical to biochemical properties, however, common instrument-based methods cannot locate double bonds in fatty acid methyl esters (FAME), the predominant analysis form of fatty acids. A recently described mass spectrometry (MS) method for locating double bonds in FAME is reported here for the analysis of minor (<1%) components of real FAME mixtures derived from three natural sources; golden algae (Schizochytrium sp.), primate brain white matter, and transgenic mouse liver. Acetonitrile chemical ionization tandem MS was used to determine double bond positions in 39 FAME, most at concentrations well below 1% of all fatty acid methyl esters. FAME identified in golden algae are 14:1n-6, 14:3n-3, 16:1n-7, 16:2n-6, 16:3n-6, 16:3n-3, 16:4n-3, 18:2n-7, 18:3n-7, 18:3n-8, 18:4n-3, 18:4n-5, 20:3n-7, 20:4n-3, 20:4n-5, 20:4n-7, 20:5n-3, and 22:4n-9. Additional FAME identified in primate brain white matter are 20:1n-7, 20:1n-9, 20:2n-7, 20:2n-9, 22:1n-7, 22:1n-9, 22:1n-13, 22:2n-6, 22:2n-7, 22:2n-9, 22:3n-6, 22:3n-7, 22:3n-9, 22:4n-6, 24:1n-7, 24:1n-9, and 24:4n-6. Additional FAME identified in mouse liver are 26:5n-6, 26:6n-3, 28:5n-6, and 28:6n-3. The primate brain 22:3n-7 and algae 18:4n-5 are novel fatty acids. These results demonstrate the usefulness of the technique for analysis of real samples. Tables are presented to aid in interpretation of acetonitrile CIMS/MS spectra. PMID:12202254

Michaud, Anthony L; Diau, Guan-Yeu; Abril, Reuben; Brenna, J Thomas

2002-08-15

317

Atmospheric pressure covalent adduct chemical ionization tandem mass spectrometry for double bond localization in monoene- and diene-containing triacylglycerols.  

PubMed

We report a method to elucidate the structure of triacyl-glycerols (TAGs) containing monoene or diene fatty acyl groups by atmospheric pressure covalent adduct chemical ionization (APCACI) tandem mass spectrometry using acetonitrile as an adduct formation reagent. TAGs were synthesized with the structures ABB and BAB, where A is palmitate (C16:0) and B is an isomeric C18 monoene unsaturated at position 9, 11, or 13 or an isomeric diene unsaturated at positions 9 and 11, 10 and 12, or 9 and 12. In addition to the species at m/z 54 observed in previous CI studies of fatty acid methyl esters, we also found that ions at m/z 42, 81, and 95 undergo covalent reaction with TAGs containing double bonds to yield ions at m/z 40, 54, 81, and 95 units greater than that of the parent TAG: [M + 40]+, [M + 54]+, [M + 81]+, and [M + 95]+ ions. When collisionally dissociated, these ions fragment to produce two or three diagnostic ions that locate the double bonds in the TAG. In addition, ions [RCH=C=O + 40]+ and [RCH=C=O + 54]+ formed from collisional dissociation are of strong abundance in MS/MS spectra, and collisional activation of these ions produces two intense confirmatory diagnostic ions in the MS3 spectra. Fragment ions reflecting neutral loss of an sn-1-acyl group from [M + 40]+ and [M + 54]+ are more abundant than those reflecting neutral loss of an sn-2-acyl group, analogous to previous reports for protonated TAGs. The position of each acyl group on the glycerol backbone is thus determined by the relative abundances of these ions. Under the conditions in our instrument, the [M + 40]+ adduct is at the highest signal and also yields all information about the double bond position and TAG stereochemistry. With the exception of geometries about the double bonds, racemic TAG isomers containing two monoenes or dienes and a saturate can be fully characterized by APCACI-MS/MS/MS. PMID:17279727

Xu, Yichuan; Brenna, J Thomas

2007-02-06

318

Ionization structure and chemical abundances of the Wolf-Rayet nebula NGC 6888 with integral field spectroscopy  

NASA Astrophysics Data System (ADS)

Context. The study of nebulae around Wolf-Rayet (WR) stars gives us clues about the mass-loss history of massive stars, as well as about the chemical enrichment of the interstellar medium (ISM). Aims: This work aims to search for the observational footprints of the interactions between the ISM and stellar winds in the WR nebula NGC 6888 in order to understand its ionization structure, chemical composition, and kinematics. Methods: We have collected a set of integral field spectroscopy observations across NGC 6888, obtained with PPAK in the optical range performing both 2D and 1D analyses. Attending to the 2D analysis in the northeast part of NGC 6888, we have generated maps of the extinction structure and electron density. We produced statistical frequency distributions of the radial velocity and diagnostic diagrams. Furthermore, we performed a thorough study of integrated spectra in nine regions over the whole nebula. Results: The 2D study has revealed two main behaviours. We have found that the spectra of a localized region to the southwest of this pointing can be represented well by shock models assuming n = 1000 cm-3, twice solar abundances, and shock velocities from 250 to 400 km s-1. With the 1D analysis we derived electron densities ranging from <100 to 360 cm-3. The electron temperature varies from ~7700 K to ~10 200 K. A strong variation of up to a factor 10 between different regions in the nitrogen abundance has been found: N/H appears lower than the solar abundance in those positions observed at the edges and very enhanced in the observed inner parts. Oxygen appears slightly underabundant with respect to solar value, whereas the helium abundance is found to be above it. We propose a scenario for the evolution of NGC 6888 to explain the features observed. This scheme consists of a structure of multiple shells: i) an inner and broken shell with material from the interaction between the supergiant and WR shells, presenting an overabundance in N/H and a slight underabundance in O/H; ii) an outer shell very intense in [OIII]?5007 Å corresponding to the main sequence bubble broken up as a consequence of the collision between supergiant and WR shells. Nitrogen and oxygen do not appear enhanced here, but helium appears enriched; iii) and finally it includes an external and faint shell that surrounds the whole nebula like a thin skin representing the early interaction between the winds from the main sequence star with the ISM for which typical circumstellar abundances are derived. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Table 3 is available in electronic form at http://www.aanda.org

Fernández-Martín, A.; Martín-Gordón, D.; Vílchez, J. M.; Pérez Montero, E.; Riera, A.; Sánchez, S. F.

2012-05-01

319

Negative-tone polyphenol resist based on chemically amplified polarity change reaction with sub-50 nm resolution capability  

NASA Astrophysics Data System (ADS)

We designed a novel chemically-amplified negative-tone molecular-resist compound of 3M6C-MBSA-BL, which is a ?-hydroxycarboxylated polyphenol (4,4'-methylenebis[2-[di(2-methyl-4-hydroxy-5-cyclohexylphenyl)] methyl]phenol (3M6C-MBSA)) for EB and EUV lithographies to be used in hp 45 and beyond technology nodes. After selection of photo acid generators (PAGs) and optimization of the concentration of PAG in the resist, we could demonstrate 40-nm line and space patterns resolution by EB exposure. Also dry-etching durability and 1-month shelf life at -20oC were confirmed. Small line-edge roughness (LER) values of 4.5 nm (inspection length: L = 620 nm) and 6.2 nm (L = 1800 nm) were achieved using the 3M6C-MBSA-BL resist.

Kojima, Kyoko; Hattori, Takashi; Fukuda, Hiroshi; Hirayama, Taku; Shiono, Daiju; Hada, Hideo; Onodera, Junichi

2006-03-01

320

Dual parallel electrospray ionization and atmospheric pressure chemical ionization mass spectrometry (MS), MS/MS and MS/MS/MS for the analysis of triacylglycerols and triacylglycerol oxidation products.  

PubMed

Two mass spectrometers, in parallel, were employed simultaneously for analysis of triacylglycerols in canola oil, for analysis of triolein oxidation products, and for analysis of triacylglycerol positional isomers separated using reversed-phase high-performance liquid chromatography. A triple quadrupole mass spectrometer was interfaced via an atmospheric pressure chemical ionization (APCI) interface to two reversed-phase liquid chromatographic columns in series. An ion trap mass spectrometer was coupled to the same two columns using an electrospray ionization (ESI) interface, with ammonium formate added as electrolyte. Electrospray ionization mass spectrometry (ESI-MS) under these conditions produced abundant ammonium adduct ions from triacylglycerols, which were then fragmented to produce MS/MS spectra and then fragmented further to produce MS/MS/MS spectra. ESI-MS/MS of the ammoniated adduct ions gave product ion mass spectra which were similar to mass spectra obtained by APCI-MS. ESI-MS/MS produced diacylglycerol fragment ions, and additional fragmentation (MS/MS/MS) produced [RCO](+) (acylium) ions, [RCOO+58](+) ions, and other related ions which allowed assignment of individual acyl chain identities. APCI-MS of triacylglycerol oxidation products produced spectra like those reported previously using APCI-MS. APCI-MS/MS produced ions related to individual fatty acid chains. ESI-MS of triacylglycerol oxidation products produced abundant ammonium adduct ions, even for those molecules which previously produced little or no intact molecular ions under APCI-MS conditions. Fragmentation (MS/MS) of the [M+NH(4)](+) ions produced results similar to those obtained by APCI-MS. Further fragmentation (MS/MS/MS) of the diacylglycerol fragments of oxidation products provided information on the oxidized individual fatty acyl chains. ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols. PMID:11816045

Byrdwell, Wm Craig; Neff, William E

2002-01-01

321

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

2013-09-11

322

Physicochemical modelling of negative corona in oxygen: the effect of boundaries  

Microsoft Academic Search

Negative corona discharge in pure oxygen is numerically investigated by means of a physicochemical model that considers both elementary plasma processes (ionization, electron attachment and detachment, ion recombination, etc.) and chemical reactions between neutral species. The chemical kinetics model and the electrical model are coupled through Poisson's equation. The effect of ozone decomposition on the walls and its influence on

F. Pontiga; C. Soria; A. Castellanos; J. D. Skalny

2002-01-01

323

Thermochemistry of organic and heteroorganic species. Part XIII. Structural aspects and thermochemical approach to isomerization and fragmentation of negative ions. Simple bond cleavage and hydrogen rearrangement processes  

Microsoft Academic Search

Many hundreds of isomerization and fragmentation processes for negatively charged ions obtained in electron attachment dissociation, collision induced dissociation and negative chemical ionization have been analyzed to find out certain regularities in gas-phase monomolecular chemistry of negative ions like it was earlier performed for positive ions [Eur. J. Mass Spectrom., 8 (2002) 409]. This analysis combined with systematic application of

Dmitry Ponomarev; Viatcheslav Takhistov

2006-01-01

324

Performance evaluation of gas chromatography-atmospheric pressure chemical ionization-time-of-flight mass spectrometry for metabolic fingerprinting and profiling.  

PubMed

Gas chromatography-atmospheric-pressure chemical ionization-time-of-flight mass spectrometry (GC-APCI-TOFMS) was compared to GC × GC-electron ionization (EI)-TOFMS, GC-EI-TOFMS, GC-chemical ionization (CI)-quadrupole mass spectrometry (qMS), and GC-EI-qMS in terms of reproducibility, dynamic range, limit of detection, and quantification using a mix of 43 metabolites and 12 stable isotope-labeled standards. Lower limits of quantification for GC-APCI-TOFMS ranged between 0.06 and 7.81 ?M, and relative standard deviations for calibration replicates were between 0.4% and 8.7%. For all compounds and techniques, except in four cases, R(2) values were above 0.99. Regarding limits of quantification, GC-APCI-TOFMS was inferior to only GC × GC-EI-TOFMS, but outperformed all other techniques tested. GC-APCI-TOFMS was further applied to the metabolic fingerprinting of two Escherichia coli strains. Of 45 features that differed significantly (false discovery rate < 0.05) between the strains, 25 metabolites were identified through highly accurate and reproducible (?m ± SD below 5 mDa over m/z 190-722) mass measurements. Starting from the quasimolecular ion, six additional metabolites were identified that had not been found in a previous study using GC × GC-EI-TOFMS and an EI mass spectral library for identification purposes. Silylation adducts formed in the APCI source assisted the identification of unknown compounds, as their formation is structure-dependent and is not observed for compounds lacking a carboxylic group. PMID:21859117

Wachsmuth, Christian J; Almstetter, Martin F; Waldhier, Magdalena C; Gruber, Michael A; Nürnberger, Nadine; Oefner, Peter J; Dettmer, Katja

2011-09-09

325

The effect of H2SO4 - amine clustering on chemical ionization mass spectrometry (CIMS) measurements of gas-phase sulfuric acid  

NASA Astrophysics Data System (ADS)

The state-of-the art method for measuring atmospheric gas-phase sulfuric acid is chemical ionization mass spectrometry (CIMS) based on nitrate reagent ions. We have assessed the possible effect of the sulfuric acid molecules clustering with base molecules on CIMS measurements using computational chemistry. From the computational data, three conclusions can be drawn. First, a significant fraction of the gas-phase sulfuric acid molecules are very likely clustered with amines if the amine concentration is around or above a few ppt. Second, some fraction of these acid-amine clusters may not be charged by the CIMS instrument, though the most reliable computational methods employed predict this fraction to be small; on the order of ten percent or less. Third, the amine molecules will evaporate practically immediately after charging, thus evading detection. These effects may need to be taken into account in the interpretation of atmospheric measurement data obtained using chemical ionization methods. The purpose of this study is not to criticize the CIMS method, but to help understand the implications of the measured results.

Kurtén, T.; Petäjä, T.; Smith, J.; Ortega, I. K.; Sipilä, M.; Junninen, H.; Ehn, M.; Vehkamäki, H.; Mauldin, L.; Worsnop, D. R.; Kulmala, M.

2011-03-01

326

Technical Note: Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds  

NASA Astrophysics Data System (ADS)

The performance of a new chemical ionization reaction time-of-flight mass spectrometer (CIR-TOF-MS) utilising the environment chamber SAPHIR (Simulation of Atmospheric Photochemistry In a large Reaction Chamber- Forschungzentrum Jülich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composition and Change the European NeTwork for excellence) supported oxygenated volatile organic compound (OVOC) measurement intercomparison during January 2005. The experiment entailed the measurement of 14 different atmospherically significant OVOCs at various mixing ratios in the approximate range 10.0-0.6 ppbV. The CIR-TOF-MS operated throughout the exercise with the hydronium ion (H3O+) as the primary chemical ionization (CI) reagent in order to facilitate proton transfer to the analyte OVOCs. The results presented show that the CIR time-of-flight mass spectrometer is capable of detecting a wide range of atmospheric OVOCs at mixing ratios of around 10 ppbV in "real-time" (i.e. detection on the one-minute time scale), with sub-ppbV measurement also achieved following an increase in averaging time to tens of minutes. It is shown that in general OVOC measurement is made with high accuracy and precision, with integration time, mixing ratio and compound dependent values as good as 4-13% and 3-15% respectively. It is demonstrated that CIR-TOF-MS has rapid multi-channel response at the required sensitivity, accuracy and precision for atmospheric OVOC measurement.

Wyche, K. P.; Blake, R. S.; Ellis, A. M.; Monks, P. S.; Brauers, T.; Koppmann, R.; Apel, E. C.

2007-02-01

327

Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds  

NASA Astrophysics Data System (ADS)

The performance of a new chemical ionization reaction time-of-flight mass spectrometer (CIR-TOF-MS) utilising the environment chamber SAPHIR (Simulation of Atmospheric Photochemistry In a large Reaction Chamber - Forschungzentrum Jülich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composition and Change the European NeTwork for excellence) supported oxygenated volatile organic compound (OVOC) measurement intercomparison during January 2005. The experiment entailed the measurement of 14 different atmospherically significant OVOCs at various mixing ratios in the approximate range 10.0-0.6 ppbV. The CIR-TOF-MS operated throughout the exercise with the hydronium ion (H3O+) as the primary chemical ionization (CI) reagent in order to facilitate proton transfer to the analyte OVOCs. The results show the CIR time-of-flight mass spectrometer is capable of detecting a wide range of atmospheric OVOCs down to sub-ppbV mixing ratios with high accuracy and precision. It is demonstrated that the technique has rapid multi-channel response at the required sensitivity, accuracy and precision for atmospheric OVOC measurements.

Wyche, K. P.; Blake, R. S.; Ellis, A. M.; Monks, P. S.; Brauers, T.; Koppmann, R.; Apel, E.

2006-10-01

328

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

PubMed

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

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

2013-01-21

329

Identification of volatile and semivolatile compounds in chemical ionization GC-MS using a mass-to-structure (MTS) Search Engine with integral isotope pattern ranking.  

PubMed

The mass-to-structure or MTS Search Engine is an Access 2010 database containing theoretical molecular mass information for 19,438 compounds assembled from common sources such as the Merck Index, pesticide and pharmaceutical compilations, and chemical catalogues. This database, which contains no experimental mass spectral data, was developed as an aid to identification of compounds in atmospheric pressure ionization (API)-LC-MS. This paper describes a powerful upgrade to this database, a fully integrated utility for filtering or ranking candidates based on isotope ratios and patterns. The new MTS Search Engine is applied here to the identification of volatile and semivolatile compounds including pesticides, nitrosoamines and other pollutants. Methane and isobutane chemical ionization (CI) GC-MS spectra were obtained from unit mass resolution mass spectrometers to determine MH(+) masses and isotope ratios. Isotopes were measured accurately with errors of <4% and <6%, respectively, for A + 1 and A + 2 peaks. Deconvolution of interfering isotope clusters (e.g., M(+) and [M - H](+)) was required for accurate determination of the A + 1 isotope in halogenated compounds. Integrating the isotope data greatly improved the speed and accuracy of the database identifications. The database accurately identified unknowns from isobutane CI spectra in 100% of cases where as many as 40 candidates satisfied the mass tolerance. The paper describes the development and basic operation of the new MTS Search Engine and details performance testing with over 50 model compounds. PMID:23248816

Liao, Wenta; Draper, William M

2013-02-21

330

The application of isotope dilution thermal ionization mass spectrometry to traceability of chemical measurement and interlaboratory comparisons  

Microsoft Academic Search

In this work, the method of isotope dilution thermal ionization mass spectrometry able to trace to SI was developed to accurately\\u000a measure trace amount of Cd, Pb, Zn and Cu in sediment, rice, wine, and human serum samples for interlaboratory comparisons.\\u000a The research focuses on how to apply the primary method correctly, uncertainty evaluation of measurement results, and how\\u000a to

Jun Wang; Motain Zhao; Na Guan; Hai Lu

2006-01-01

331

Analysis of estrogens in river water and effluents using solid-phase extraction and gas chromatography–negative chemical ionisation mass spectrometry of the pentafluorobenzoyl derivatives  

Microsoft Academic Search

A procedure was developed for the analysis of estrogens in environmental water and effluents. Samples were extracted by passing through polymer-impregnated solid-phase extraction discs or C18 cartridges, followed by gas chromatography–negative chemical ionisation mass spectrometry of the pentafluorobenzoyl derivatives. The derivatives were stable and gave diagnostic negative molecular ions as the base peak for each of the major estrogens studied.

Xiao-Yao Xiao; David V McCalley; James McEvoy

2001-01-01

332

Fragmentation energy index for universalization of fragmentation energy in ion trap mass spectrometers for the analysis of chemical weapon convention related chemicals by atmospheric pressure ionization-tandem mass spectrometry analysis.  

PubMed

The use of mass spectra generated at 70 eV in electron ionization (EI) as a universal standard for EI has helped in the generation of searchable library databases and had a profound influence on the analytical applications of gas chromatography/mass spectrometry (GC/MS), similarly for liquid chromatography tandem mass spectrometry (LC-MS/MS), suggesting a novel method to normalize the collisional energy for the universalization of fragmentation energy for the analysis of Chemical Weapon Convention (CWC)-related chemicals by atmospheric pressure ionization-tandem mass spectrometry (API-MS(n)) using three-dimensional (3D) ion trap instruments. For normalizing fragmentation energy a "fragmentation energy index" (FEI) is proposed which is an arbitrary scale based on the fact of specific MS/MS fragmentation obtained at different collisional energies for the reference chemicals which are not CWC scheduled compounds. FEI 6 for the generation of an MS(n) library-searchable mass spectral database is recommended. PMID:19331429

Palit, Meehir; Mallard, Gary

2009-04-01

333

Misuse of null hypothesis significance testing: would estimation of positive and negative predictive values improve certainty of chemical risk assessment?  

PubMed

Although generally misunderstood, the p value is the probability of the test results or more extreme results given H0 is true: it is not the probability of H0 being true given the results. To obtain directly useful insight about H0, the positive predictive value (PPV) and the negative predictive value (NPV) may be useful extensions of null hypothesis significance testing (NHST). They provide information about the probability of statistically significant and non-significant test outcomes being true based on an a priori defined biologically meaningful effect size. The present study explores the utility of PPV and NPV in an ecotoxicological context by using the frequently applied Daphnia magna reproduction test (OECD guideline 211) and the chemical stressor lindane as a model system. The results indicate that especially the NPV deviates meaningfully between a test design strictly following the guideline and an experimental procedure controlling for ? and ? at the level of 0.05. Consequently, PPV and NPV may be useful supplements to NHST that inform the researcher about the level of confidence warranted by both statistically significant and non-significant test results. This approach also reinforces the value of considering ?, ?, and a biologically meaningful effect size a priori. PMID:23625122

Bundschuh, Mirco; Newman, Michael C; Zubrod, Jochen P; Seitz, Frank; Rosenfeldt, Ricki R; Schulz, Ralf

2013-04-28

334

REVIEW ARTICLE: Again `why layered, square-planar, mixed-valent cuprates alone?' - further pursuit of the `chemical' negative-U route to the HTSC mechanism  

Microsoft Academic Search

This paper is a consolidated presentation of why the author believes the most promising way forward as regards the mechanism for high-temperature superconductivity remains with the `chemical negative-U' interpretation, first sketched out in 1987. Many other mechanisms have been proposed over the years but none address head on the problem as to why the phenomenon is so tightly confined to

John A. Wilson

2000-01-01

335

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

336

[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

337

Characterization of triacylglycerol and diacylglycerol composition of plant oils using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

Triacylglycerols (TGs) and diacylglycerols (DGs) in 16 plant oil samples (hazelnut, pistachio, poppy-seed, almond, palm, Brazil-nut, rapeseed, macadamia, soyabean, sunflower, linseed, Dracocephalum moldavica, evening primrose, corn, amaranth, Silybum arianum) were analyzed by HPLC-MS with atmospheric pressure chemical ionization (APCI) and UV detection at 205 nm on two Nova-Pak C18 chromatographic columns connected in series. A single chromatographic column and non-aqueous ethanol-acetonitrile gradient system was used as a compromise between the analysis time and the resolution for the characterization of TG composition of five plant oils. APCI mass spectra were applied for the identification of all TGs and other acylglycerols. The isobaric positional isomers can be distinguished on the basis of different relative abundances of the fragment ions formed by preferred losses of the fatty acid from sn-1(3) positions compared to the sn-2 position. Excellent chromatographic resolution and broad retention window together with APCI mass spectra enabled positive identification of TGs containing fatty acids with odd numbers of carbon atoms such as margaric (C17:0) and heptadecanoic (C17:1) acids. The general fragmentation patterns of TGs in both APCI and electrospray ionization mass spectra were proposed on the basis of MSn spectra measured with an ion trap analyzer. The relative concentrations of particular TGs in the analyzed plant oils were estimated on the basis of relative peak areas measured with UV detection at 205 nm. PMID:12974290

Holcapek, Michal; Jandera, Pavel; Zderadicka, Petr; Hrubá, Lucie

2003-08-29

338

A positive chemical ionization GC/MS method for the determination of airborne ethylene glycol and propylene glycols in non-occupational environments.  

PubMed

An analytical method for ethylene glycol and propylene glycols has been developed for measuring airborne levels of these chemicals in non-occupational environments such as residences and office buildings. The analytes were collected on charcoal tubes, solvent extracted, and analyzed by gas chromatography-mass spectrometry using a positive chemical ionization technique. The method had a method detection limit of 0.07 microg m(-3) for ethylene glycol and 0.03 microg m(-3) for 1,2- and 1,3-propylene glycols, respectively, based on a 1.44 m3 sampling volume. Indoor air samples of several residential homes and other indoor environments have been analyzed. The median concentrations of ethylene glycol and 1,2-propylene glycol in nine residential indoor air samples were 53 microg m(-3) and 13 microg m(-3) respectively with maximum values of 223 microg m(-3) and 25 microg m(-3) detected for ethylene glycol and 1,2-propylene glycol respectively. The concentrations of these two chemicals in one office and two laboratories were at low microg m(-3) levels. The maximum concentration of 1,3-propylene glycol detected in indoor air was 0.1 microg m(-3). PMID:15536501

Zhu, Jiping; Feng, Yong-Lai; Aikawa, Bio

2004-09-24

339

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

340

Quantitation of fourteen urinary alpha-amino acids using isobutane gas chromatography chemical ionization mass spectrometry with 13C amino acids as internal standards.  

PubMed

Isobutane chemical ionization gas chromatography mass spectometry of the N-trifluoroacetyl-carboxy-n-butyl ester derivatives of amino acids, using a commercial per-13C-amino acid mixture as internal standards, provided a sensitive and specific method for quantitative analysis of fourteen urinary alpha-amino acids. A computer controlled quadrupole mass spectrometer was used in a selected ion monitoring mode to record the ion current due to the protonated molecular ions of each alpha-amino acid/13C analogue pair. BASIC programmes located peak maxima, and using previously established standard curves, calculated the amino acid content on the bases of both peak height and peak area ratios. Duplicate amino acid analyses are possible on 5 microliter of urine. Instrumental analysis required 25 minutes, automated data processing 10 minutes, and sample preparation 2 hours. Detection limits approached 1 ng with a typical mean standard deviation of 2% for the instrumental analysis. PMID:6452181

Finlayson, P J; Christopher, R K; Duffield, A M

1980-10-01

341

A preconcentrator coupled to a GC/FTMS: advantages of self-chemical ionization, mass measurement accuracy, and high mass resolving power for GC applications.  

PubMed

Coupling of a cryogenic preconcentrator (PC) to a gas chromatograph/Fourier transform ion cyclotron resonance mass spectrometer (GC/FT-ICR MS) is reported. To demonstrate the analytical capabilities of the PC/GC/FT-ICR MS, headspace samples containing volatile organic compounds (VOCs) emitted from detached pine tree twigs were analyzed. Sub-ppm mass measurement accuracy (MMA) for highly resolved (m/Deltam(50%) > 150 k) terpene ions was achieved. Direct PC/GC/FT-ICR MS analyses revealed that detached twigs from pine trees emit acetone, camphor, and four detectable hydrocarbon isomers with C(10)H(16) empirical formula. The unknown analytes were identified based on accurate mass measurement and their mass spectral appearances. Authentic samples were used to confirm initially unknown identifications. Self-chemical-ionization (SCI) reactions furnished an additional dimension for rapid isomer differentiation of GC eluents in real time. PMID:15276166

Solouki, Touradj; Szulejko, Jan E; Bennett, Justin B; Graham, LeRae B

2004-08-01

342

A sensitive and specific method for the determination of chlorimipramine and desmethylchlorimipramine in plasma using selected ion monitoring with chemical ionization.  

PubMed

Chlorimipramine and other tricyclic antidepressant drugs are widely used for the treatment of depressive disorders. We analysed chlorimipramine and its major metabolite desmethylchlorimipramine after a two step extraction from plasma with diethylether. The underivatized samples were separated on a short (40 cm x 2 mm) silanized glass column packed with 3% OV 17 on Chromosorb HPW-DMCS, 80-100 mesh, which was directly coupled to the mass spectrometer. Detection of the tricyclic antidepressant drugs and their respective deuterium labelled internal standards was performed by chemical ionization using methanol vapour as reactant gas. The method is simple and sufficiently sensitive to permit the routine analysis of therapeutic plasma levels of tricyclic antidepressant drugs in extracts originating from 1 ml plasma. PMID:7225541

Lapin, A; Karobath, M

1980-11-01

343

Determination of gamma-hydroxybutyric acid (GHB) in plasma and urine by headspace solid-phase microextraction and gas chromatography/positive ion chemical ionization mass spectrometry.  

PubMed

A new method for the qualitative and quantitative analysis of gamma-hydroxybutyric acid (GHB) in plasma and urine samples is described. It involves the conversion of GHB to gamma-butyrolactone (GBL), its subsequent headspace solid-phase microextraction (SPME), and detection by gas chromatography/positive ion chemical ionization mass spectrometry (GC/PICI-MS), using D(6)-GBL as internal standard. The assay is linear over a plasma GHB range of 1-100 microg/mL (n = 5, r = 0.999) and a urine GHB range of 5-150 microg/mL (n = 5, r = 0. 998). Relative intra- and inter-assay standard deviations, determined for plasma and urine samples at 5 and 50 microg/mL, are all below 5%. The method is simple, specific and reasonably fast. It may be applied for clinical and forensic toxicology as well as for purposes of therapeutic drug monitoring. PMID:11114057

Frison, G; Tedeschi, L; Maietti, S; Ferrara, S D

2000-01-01

344

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

345

Analysis of aldehydes in beer by gas-diffusion microextraction: characterization by high-performance liquid chromatography-diode-array detection-atmospheric pressure chemical ionization-mass spectrometry.  

PubMed

In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis. PMID:20451914

Gonçalves, Luís Moreira; Magalhães, Paulo Jorge; Valente, Inês Maria; Pacheco, João Grosso; Dostálek, Pavel; Sýkora, David; Rodrigues, José António; Barros, Aquiles Araújo

2010-04-09

346

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

347

Eddy Correlation Measurements of the Air\\/Sea Flux of DMS Using Atmospheric Pressure Chemical Ionization Mass Spectrometry  

Microsoft Academic Search

The physical and chemical processes controlling gas exchange across the air\\/sea interface are not well understood. Many laboratory and field studies of the physical controls on gas exchange have been performed using indirect mass balance measurement techniques, but there have been few direct gas flux measurements over the ocean. Eddy correlation is a micrometeorological technique, which can measure fluxes directly.

C. A. Marandino; W. J. Debruyn; E. S. Saltzman

2003-01-01

348

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

349

Differentiation and classification of user-specified bacterial groups by in situ thermal hydrolysis and methylation of whole bacterial cells with tert-butyl bromide chemical ionization ion trap mass spectrometry  

Microsoft Academic Search

Fatty acid methyl esters (FAMEs) from 20 bacterial samples, formed through in situ thermal hydrolysis and methylation (THM) of lipids from whole bacterial cells using tetramethylammonium hydroxide, have been investigated by t-butyl bromide chemical ionization (CI) ion trap mass spectrometry (MS). The mass spectra, in the early portion of the total ion profile, contained as major peaks the protonated saturated

Ming Xu; Franco Basile; Kent J Voorhees

2000-01-01

350

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

351

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

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; Burnham, Carey-Ann D

2013-02-20

352

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.

Ford, Bradley A.

2013-01-01

353

Complex therapeutical effect of ionized air: stimulation of the immune system and decrease in excessive serotonin. H2O2 as a link between the two counterparts  

Microsoft Academic Search

We investigated the therapeutic effect of breathing ionized air in patients with chronic inflammation and decreased immune reactivity. Air ions were generated by an electroionizer, Tchijevsky Lustre. The air at the place of breathing contained 120 000 negative charges\\/cm3. By chemical nature, the negative air ions are superoxide at a concentration of less than 1 ?M, and hydrogen peroxide at

Vladimir P. Tikhonov; Andrei A. Temnov; Vladimir A. Kushnir; Tatyana V. Sirota; Elena G. Litvinova; Marina V. Zakharchenko; Marie N. Kondrashova

2004-01-01

354

Characterization of a thermal decomposition chemical ionization mass spectrometer for the measurement of peroxy acyl nitrates (PANs) in the atmosphere  

NASA Astrophysics Data System (ADS)

This paper presents a detailed laboratory characterization of a thermal dissociation ionization mass spectrometer (TD-CIMS) for the atmospheric measurement of Peroxyacetyl nitrate (PAN) and its homologues. PANs are efficiently dissociated in a heated inlet tube and the resulting peroxy acyl radicals are reacted with I- ions in a flow tube. The CIMS detects the corresponding carboxylate ions to give a specific and quantitative measurement of each PAN species. PAN, peroxypropionyl nitrate (PPN), peroxyisobutyryl nitrate (PiBN), peroxy-n-butyryl nitrate (PnBN), peroxyacryloyl nitrate (APAN), peroxycrotonyl nitrates (CPAN) and peroxymethacryloyl nitrate (MPAN) were cross-calibrated with both a dual channel GC/ECD and a total odd-nitrogen (NOy) instrument for the NCAR TD-CIMS' typical aircraft operation conditions. In addition, the instrument sensitivity to a number of more exotic PAN homologues (peroxyhydroxyacetyl nitrate, methoxyformyl peroxynitrate, and peroxybenzoyl nitrate) was evaluated qualitatively by comparisons with a long-path FTIR instrument. The sensitivity for PPN is slightly higher than that of PAN. Larger aliphatic and olefinic PAN compounds generally showed lower sensitivities. These differences are owing to secondary reactions in the thermal decomposition region, which either reduce the yield of peroxy acyl radicals or cause losses of these radicals through intramolecular decomposition. The relative importance of these secondary reactions varies considerably between different PAN species. Results also indicate that the reaction of the peroxy acyl radicals with the ion-water cluster, I-(H2O)n proceeds about an order of magnitude faster than with I- alone. Variations among the individual PAN species at very low water vapor were observed. The results call for careful evaluation of each PAN species to be measured and for each desired operating condition of a TD-CIMS instrument.

Zheng, W.; Flocke, F. M.; Tyndall, G. S.; Swanson, A.; Orlando, J. J.; Roberts, J. M.; Huey, L. G.; Tanner, D. J.

2011-03-01

355

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

PubMed

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 Capped (10 mmx2 mm) cartridge without any evaporation step. Using the back-flush mode, the analytes were transferred onto an analytical column (XTerra C18, 50 mmx4.6 mm) for chromatographic separation and mass spectrometry detection. One of the particularities of the assay is that the SPE cartridge is used as a column switching device and not as an SPE cartridge. Therefore, the same SPE cartridge could be used more than 28 times, significantly reducing the analysis cost. APCI ionization was selected to overcome any potential matrix suppression effects because the analyte and IS co-eluted. The mean precision and accuracy in the concentration range 2.5-200 ng/mL was found to be 103% and 7.4%, respectively. The data was assessed from QC samples during the validation phase of the assay. The lower limit of quantification was 2.5 ng/mL, using a 250 microL plasma aliquot. The LC-MS/MS method provided the requisite selectivity, sensitivity, robustness accuracy and precision to assess pharmacokinetics of the compound in several hundred human plasma samples. PMID:15866498

Bourgogne, Emmanuel; Grivet, Chantal; Hopfgartner, Gérard

2005-04-11

356

Analysis of epoxyeicosatrienoic acids by chiral liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry using [13C]-analog internal standards  

PubMed Central

The metabolism of arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) is thought to be mediated primarily by the cytochromes P450 (P450s) from the 2 family (2C9, 2C19, 2D6, and 2J2). In contrast, P450s of the 4 family are primarily involved in omega oxidation of AA (4A11 and 4A22). The ability to determine enantioselective formation of the regioisomeric EETs is important in order to establish their potential biological activities and to asses which P450 isoforms are involved in their formation. It has been extremely difficult to analyze individual EET enantiomers in biological fluids because they are present in only trace amounts and they are extremely difficult to separate from each other. In addition, the deuterium-labeled internal standards that are commonly used for stable isotope dilution liquid chromatography/mass spectrometry (LC/MS) analyses have different LC retention times when compared with the corresponding protium forms. Therefore, quantification by LC/MS-based methodology can be compromised by differential suppression of ionization of the closely eluting isomers. We report the preparation of [13C20]-EET analog internal standards and the use of a validated high-sensitivity chiral LC/electron capture atmospheric pressure chemical ionization (ECAPCI)-MS method for the trace analysis of endogenous EETs as their pentafluorobenzyl (PFB) ester derivatives. The assay was then used to show the exquisite enantioselectivity of P4502C19-, P4502D6-, P4501A1-, and P4501B1-mediated conversion of AA into EETs and to quantify the enantioselective formation of EETs produced by AA metabolism in a mouse epithelial hepatoma (Hepa) cell line.

Mesaros, Clementina; Lee, Seon Hwa; Blair, Ian A.

2012-01-01

357

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

PubMed

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

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

2011-12-06

358

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

359

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

360

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

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

2013-10-15

361

The fractional ionization in dark molecular clouds  

NASA Astrophysics Data System (ADS)

Aims:We have studied the mechanisms which govern the degree of ionization of the gas in molecular clouds and prestellar cores, with a view to interpreting the relative abundances of the carbon-chain species C{ n}H and their negative ions, C{n}H^-. Methods: We followed the chemical evolution of a medium comprising gas and dust as it evolves towards its steady-state composition. Various assumptions were made concerning the grain size-distribution and the fraction of very small grains (in practice, PAH), as well as the cosmic ray ionization rate. Particular attention was paid to reactions which determine the fractional ionization of the gas and the charge of the grains. Results: We found that the abundance ratio n(C6H^-)/n(C6H) is determined essentially by the ratio of the free electron density to the density of atomic hydrogen. A model with a high fractional abundance of PAH and a low fractional abundance of electrons yields agreement to a factor of 2 with the value of the ratio C6H^-:C6H observed recently in TMC-1. However, the fractional abundances of the molecular ions HCO+ and DCO+ are then higher than observed. The best overall fit with the observations of TMC-1 is obtained when the cosmic ray ionization rate is reduced, together with the rate of removal of atomic hydrogen from the gas phase (owing to adsorption on to grains).

Flower, D. R.; Pineau Des Forêts, G.; Walmsley, C. M.

2007-11-01

362

Solidphase extraction versus solid-phase microextraction for the determination of chlorinated paraffins in water using gas chromatography–negative chemical ionisation mass spectrometry  

Microsoft Academic Search

Solid-phase extraction (SPE) and solid-phase microextraction (SPME) were evaluated for the analysis of short-chain chlorinated paraffins (SCCPs) in water samples using gas chromatography coupled to negative chemical ionisation mass spectrometry (GC-NCI-MS). For SPE optimisation, four commercially available SPE cartridges were tested and several SPE parameters, such as the elution solvent, elution volume and breakthrough volume were studied. The best results

P Castells; F. J Santos; M. T Galceran

2004-01-01

363

Preparation of negative electrodes for lithium-ion rechargeable battery by pressure-pulsed chemical vapor infiltration of pyrolytic carbon into electro-conductive forms  

Microsoft Academic Search

The plate-type negative electrodes for lithium-ion rechargeable battery were prepared by pressure-pulsed chemical vapor infiltration of pyrolytic carbon (pyrocarbon) into two sorts of conductive porous forms, that is, the carbonized paper (A) and the TiN-coated paper (B), as the conductive fillers and\\/or current collectors. The electrodes had the three-dimensionally continuous current paths in the pyrocarbon-based anodes without the organic binders

Yoshimi Ohzawa; Masami Mitani; Takako Suzuki; Vinay Gupta; Tsuyoshi Nakajima

2003-01-01

364

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

365

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

NASA Astrophysics Data System (ADS)

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

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

2002-07-01

366

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

367

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

PubMed

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

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

2012-05-08

368

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

PubMed

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

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

2012-12-01

369

Method validation for the analysis of 169 pesticides in soya grain, without clean up, by liquid chromatography-tandem mass spectrometry using positive and negative electrospray ionization.  

PubMed

Part of a comprehensive study on the comparison of different extraction methods, GC-MS(/MS) and LC-MS/MS detection methods and modes, for the analysis of soya samples is described in this paper. The validation of an acetone-based extraction method for analysis of 169 pesticides in soya, using LC-MS/MS positive and negative electrospray ionisation (ESI) mode, is reported. Samples (5 g) were soaked with 10 g water and subsequently extracted with 100 mL of a mixture of acetone, dichloromethane and light petroleum (1:1:1), in the presence of 15 g anhydrous sodium sulphate. After centrifugation, aliquots of the extract were evaporated and reconstituted in 1.0 mL of methanol, before direct injection of the final extract (corresponding with 0.05 g soya mL(-1)) into the LC-MS/MS system. Linearity, r(2) of calibration curves, instrument limit of detection/quantitation (LOD/LOQ) and matrix effect were evaluated, based on seven concentrations measured in 6-fold. Good linearity (at least r(2)> or =0.99) of the calibration curves was obtained over the range from 0.1 or 0.25 to 10.0 ng mL(-1), corresponding with pesticide concentrations in soya bean extract of 2 or 5-200 microg kg(-1). Instrument LOD values generally were 0.1 or 0.25 ng mL(-1). Matrix effects were negligible for approximately 90% of the pesticides. The accuracy, precision and method LOQ were determined via recovery experiments, spiking soya at 10, 50, 100 microg kg(-1), six replicates per level. In both ESI modes, method LOQ values were mostly 10 or 50 microg kg(-1) and more than 70% of pesticides analysed by each mode met the acceptability criteria of recovery (70-120%) and RSD (< or =20%), at one or more of the three levels studied. A fast, easy and efficient method with acceptable performance was achieved for a difficult matrix as soya, without cleanup. PMID:17222861

Pizzutti, Ionara R; de Kok, André; Zanella, Renato; Adaime, Martha B; Hiemstra, Maurice; Wickert, Cristine; Prestes, Osmar D

2007-01-12

370

Physico-chemical properties of low density polyethylene and ethylene vinyl acetate composites cross-linked by ionizing radiation  

NASA Astrophysics Data System (ADS)

Conductive polymers consisting of low density polyethylene (LDPE), ethylene vinyl acetate copolymer (EVA) and carbon black (CB) were prepared by melt mixing. LDPE/CB, EVA/CB and LDPE/EVA/CB composites were irradiated by electron beam over the range 50-200 kGy. The effect of CB content, CB type, content of the EVA and irradiation dose on the physico-chemical properties (gel content, volume resistivity, mechanical and thermal properties) was investigated. The gel content increased as a function of both increasing irradiation dose and CB content, and a significant improvement in the mechanical properties (tensile strength and elongation at break) was observed. By increasing the CB content, the volume resistivity dropped by several orders of magnitude. Thermogravimetric analysis parameters including onset temperature (Ti, °C), differential thermogravimetric peak temperature (DTG, °C) and temperatures at 50% and 95% weight losses were investigated. Thermal stability of the conductive composites was enhanced by addition of either CB or EVA and the degree of enhancement was correlated to their contents. The melt flow index decreased with incorporation of CB leading to more viscous matrix.

Basfar, A. A.; Ali, Z. I.

2011-02-01

371

Visualizing the Positive-Negative Interface of Molecular Electrostatic Potentials as an Educational Tool for Assigning Chemical Polarity  

ERIC Educational Resources Information Center

|To help in interpreting the polarity of a molecule, charge separation can be visualized by mapping the electrostatic potential at the van der Waals surface using a color gradient or by indicating positive and negative regions of the electrostatic potential using different colored isosurfaces. Although these visualizations capture the molecular…

Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

2010-01-01

372

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

373

Ultra-fast analysis of anatoxin-A using laser diode thermal desorption-atmospheric pressure chemical ionization-tandem mass spectrometry: validation and resolution from phenylalanine.  

PubMed

A novel approach for the analysis of the cyanobacterial toxin, anatoxin-a (ANA-a), in an environmentally relevant matrix, using laser diode thermal desorption-atmospheric pressure chemical ionization-tandem mass spectrometry (LDTD-APCI-MS/MS) is presented. The ultra-fast analysis time (15 s/sample) provided by the LDTD-APCI interface is strengthened by its ability to remove interference from phenylalanine (PHE), an isobaric interference in ANA-a analysis by MS/MS. Thus the LDTD-APCI interface avoids the time consuming steps of derivatization, chromatographic separation or solid-phase extraction prior to analysis. Method development and instrumental parameter optimizations were focused toward signal enhancement of ANA-a, and signal removal of a PHE interference as high as 500 ?g/L. External calibration in a complex matrix gave detection and quantification limit values of 1 and 3 ?g/L respectively, as well as good linearity (R(2) > 0.999) over nearly two orders of magnitude. Internal calibration with clomiphene (CLO) is possible and method performance was similar to that obtained by external calibration. This work demonstrated the utility of the LDTD-APCI source for ultra-fast detection and quantification of ANA-a in environmental aqueous matrices, and confirmed its ability to suppress the interference of PHE without sample preparation or chromatographic separation. PMID:23159398

Lemoine, Pascal; Roy-Lachapelle, Audrey; Prévost, Michèle; Tremblay, Patrice; Solliec, Morgan; Sauvé, Sébastien

2012-11-14

374

Carbamazepine in municipal wastewater and wastewater sludge: ultrafast quantification by laser diode thermal desorption-atmospheric pressure chemical ionization coupled with tandem mass spectrometry.  

PubMed

In this study, the distribution of the anti-epileptic drug carbamazepine (CBZ) in wastewater (WW) and aqueous and solid phases of wastewater sludge (WWS) was carried out. A rapid and reliable method enabling high-throughput sample analysis for quicker data generation, detection, and monitoring of CBZ in WW and WWS was developed and validated. The ultrafast method (15s per sample) is based on the laser diode thermal desorption-atmospheric pressure chemical ionization (LDTD-APCI) coupled to tandem mass spectrometry (MS/MS). The optimization of instrumental parameters and method application for environmental analysis are presented. The performance of the novel method was evaluated by estimation of extraction recovery, linearity, precision and detection limit. The method detection limits was 12 ng L(-1) in WW and 3.4 ng g(-1) in WWS. The intra- and inter-day precisions were 8% and 11% in WW and 6% and 9% in WWS, respectively. Furthermore, three extraction methods, ultrasonic extraction (USE), microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) with three different solvent condition such as methanol, acetone and acetonitrile:ethyle acetate (5:1, v/v) were compared on the basis of procedural blank and method recovery. Overall, ASE showed the best extraction efficiency with methanol as compared to USE and MAE. Furthermore, the quantification of CBZ in WW and WWS samples showed the presence of contaminant in all stages of the treatment plant. PMID:22967548

Mohapatra, D P; Brar, S K; Tyagi, R D; Picard, P; Surampalli, R Y

2012-05-29

375

The electron impact, chemical ionization and fast atom bombardment positive ion mass spectra of 1,2-bis(sulfonyl)methylhydrazines.  

PubMed

A series of bis(sulfonyl)-1-methylhydrazines were analyzed by positive ion electron impact (EI), chemical ionization (CI) and fast atom bombardment (FAB) mass spectrometry. Since these compounds showed activity against the L1210 leukemia, an understanding of their mass spectral behavior is important should the structural characterization of metabolites be required. FAB proved to be the most useful technique, generally providing abundant protonated molecule ion peaks, in contrast to the weak peaks observed with CI (ammonia or isobutane) and the total absence of molecular ion peaks in the EI mass spectra. In addition, utilizing FAB eliminated the problem of thermal decomposition, which was very difficult to control under EI and CI experimental conditions. Fragments observed in FAB and CI mass spectra were consistent with protonation at the methyl-bearing nitrogen. One can locate the R1 and R2 moieties relative to the methyl-bearing nitrogen in FAB and CI by assigning that nitrogen as the site of protonation, with subsequent elimination of R2SO2H. PMID:1799579

Giordano, G; Peterson, G; McMurray, W J; Shyam, K; Sartorelli, A C

1991-11-01

376

Direct detection of benzene, toluene, and ethylbenzene at trace levels in ambient air by atmospheric pressure chemical ionization using a handheld mass spectrometer.  

PubMed

The capabilities of a portable mass spectrometer for real-time monitoring of trace levels of benzene, toluene, and ethylbenzene in air are illustrated. An atmospheric pressure interface was built to implement atmospheric pressure chemical ionization for direct analysis of gas-phase samples on a previously described miniature mass spectrometer (Gao et al. Anal. Chem.2006, 78, 5994-6002). Linear dynamic ranges, limits of detection and other analytical figures of merit were evaluated: for benzene, a limit of detection of 0.2 parts-per-billion was achieved for air samples without any sample preconcentration. The corresponding limits of detection for toluene and ethylbenzene were 0.5 parts-per-billion and 0.7 parts-per-billion, respectively. These detection limits are well below the compounds' permissible exposure levels, even in the presence of added complex mixtures of organics at levels exceeding the parts-per-million level. The linear dynamic ranges of benzene, toluene, and ethylbenzene are limited to approximately two orders of magnitude by saturation of the detection electronics. PMID:19879158

Huang, Guangming; Gao, Liang; Duncan, Jason; Harper, Jason D; Sanders, Nathaniel L; Ouyang, Zheng; Cooks, R Graham

2009-09-30

377

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

PubMed

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

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

2009-12-01

378

High-throughput trace analysis of explosives in water by laser diode thermal desorption/atmospheric pressure chemical ionization-tandem mass spectrometry.  

PubMed

Harmful explosives can accumulate in natural waters in the long term during their testing, usage, storage, and dumping and can pose a health risk to humans and the environment. For the first time, attachment of small anions to neutral molecules in laser diode thermal desorption/atmospheric pressure chemical ionization was systematically investigated for the direct determination of trace nitroaromatics, nitrate esters, and nitramine explosives in water. Using ammonium chloride as an additive improved the instrument response for all the explosives tested and promoted the formation of several characteristic adduct ions. The method performs well achieving good linearity over at least 2 orders of magnitude, with coefficients of determination greater than 0.995. The resulting limits of detection are in the range of 0.009-0.092 ?g/L. River water samples were successfully analyzed by the proposed method with accuracy in the range of 96-98% and a response time of 15 s, without any further pretreatment or chromatographic separation. PMID:22746321

Badjagbo, Koffi; Sauvé, Sébastien

2012-06-12

379

Quantitation of fluoride ion released sarin in red blood cell samples by gas chromatography-chemical ionization mass spectrometry using isotope dilution and large-volume injection.  

PubMed

A new method for measuring fluoride ion released isopropyl methylphosphonofluoridate (sarin, GB) in the red blood cell fraction was developed that utilizes an autoinjector, a large-volume injector port (LVI), positive ion ammonia chemical ionization detection in the SIM mode, and a deuterated stable isotope internal standard. This method was applied to red blood cell (RBC) and plasma ethyl acetate extracts from spiked human and animal whole blood samples and from whole blood of minipigs, guinea pigs, and rats exposed by whole-body sarin inhalation. Evidence of nerve agent exposure was detected in plasma and red blood cells at low levels of exposure. The linear method range of quantitation was 10-1000 pg on-column with a detection limit of approximately 2-pg on-column. In the course of method development, several conditions were optimized for the LVI, including type of injector insert, injection volume, initial temperature, pressure, and flow rate. RBC fractions had advantages over the plasma with respect to assessing nerve agent exposure using the fluoride ion method especially in samples with low serum butyrylcholinesterase activity. PMID:15239856

Jakubowski, E M; McGuire, J M; Evans, R A; Edwards, J L; Hulet, S W; Benton, B J; Forster, J S; Burnett, D C; Muse, W T; Matson, K; Crouse, C L; Mioduszewski, R J; Thomson, S A

380

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

2009-05-03

381

A fast method for determining low-molecular-mass aliphatic carboxylic acids by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.  

PubMed

A fast quantitative high-performance liquid chromatographic separation method with atmospheric pressure chemical ionization mass spectrometric detection (HPLC-APCI-MS) was developed for the determination of low-molecular-mass aliphatic mono- and dicarboxylic acids typically present in different industrial process waters. A mixture of glycolic, lactic, a-glucoisosaccharinic, oxalic, maleic, fumaric, succinic, malic, glutaric, methylsuccinic, and adipic acids was separated using an RP chromatographic system. Adipic acid was used as an internal standard to calculate correlation coefficients for the acids studied. The chromatographic analysis of these acids was primarily carried out by means of gradient elution with an aqueous formic acid solution (0.15%, pH 2.5) and methanol using a modified C18 stationary phase. Good acid separation could be obtained for all acids by optimizing the chromatographic conditions. The method provides a simple sample preparation and faster analysis time compared to the traditional gas chromatographic methods, thus enabling almost real-time monitoring of these acids. Finally, the method developed was applied to the analysis of a complex mixture of aliphatic hydroxy carboxylic acids, which are formed as alkaline degradation products of carbohydrates during wood delignification and are present in the cooking spent liquor (black liquor). PMID:17017012

Käkölä, Jaana; Alén, Raimo

2006-08-01

382

Analysis of deuterated analogs of vitamin A by electron impact and chemical ionization modes in gas chromatography coupled to mass spectrometry.  

PubMed

To evaluate the total body reserves of vitamin A in humans, deuterated forms of vitamin A are potentially useful probes. In the present investigation, we have selected anhydroretinol as a useful indicator of retinol isolated from plasma during GC/MS analysis because of its relatively high volatility, its formation from retinol in good yield directly on GC columns, and the improbability of deuterium loss or exchange during its formation. The major drawback in its use is the extensive isomerization to cis-isomers which occurred on GC columns even under mild conditions of analysis. Favorable conditions for the GC/MS assay of anhydroretinol in the EI mode were defined. The mass spectral response is linear with the amount of retinol injected from 10 to 400 ng, and the observed sensitivity is adequate for the measurement of retinol in 1 ml of plasma. By using isobutane or methane, chemical ionization mass spectra of anhydroretinol and retinaldehyde are reported for the first time. Although both gave the expected [M + H]+ molecular ion, analysis of anhydroretinol in the EI mode was a more appropriate and sensitive measure of retinol under our assay conditions. PMID:6735613

Cullum, M E; Olson, J A; Veysey, S W

1984-01-01

383

Trace determination of 1-aminopropanone, a potential marker for wastewater contamination by liquid chromatography and atmospheric pressure chemical ionization-mass spectrometry.  

PubMed

1-Aminopropanone (APR) is a volatile aminoketone of human origin that has been identified in raw sewage and surface waters. However, the traditional methodology for the determination of APR is extremely complicated and requires a skilled chemist to achieve consistent results. This investigation presents a novel and simple method for the analysis of APR by direct derivatization in aqueous media. APR is synthesized as its hydrochloride and derivatized using mercaptoethanol and o-phthalaldehyde. The product of reaction is separated on a 15 cm x 4.6 mm Luna C-18 column (1 mL/min, 45:55 acetonitrile: Water) and detected using a single quadrupole mass spectrometer detector operated in atmospheric pressure chemical ionization (APCI) mode. Method detection limits as low as 100 nM were routinely obtained with a precision of 1.7%. Recoveries of APR were always found to be greater then 88% in surface and wastewater samples fortified at three different levels. However, despite the robustness of the method and the fact that APR was consistently detected in urine it was not present in a variety surface or wastewaters analyzed during the course of the study. These results pose a critical question on the use of APR as a tracer for human derived wastewaters. PMID:16443254

Singh, Simrat P; Gardinali, Piero R

2006-01-26

384

Ionizing radiation  

Technology Transfer Automated Retrieval System (TEKTRAN)

This chapter gives a comprehensive review on ionizing irradiation of fresh fruits and vegetables. Topics include principles of ionizing radiation, its effects on pathogenic and spoilage microorganisms, shelf-life, sensory quality, nutritional and phytochemical composition, as well as physiologic and...

385

International Commission for Protection Against Environmental Mutagens and Carcinogens. Working paper no. 6. Estimation of genetic risks of exposure to chemical mutagens: relevance of data on spontaneous mutations and of experience with ionizing radiation.  

PubMed

This paper examines the impact of advances in knowledge on the molecular biology of human Mendelian diseases on the estimation of genetic risks of exposure to ionizing radiation and to chemical mutagens. More specifically, it addresses the question of whether and to what extent naturally occurring Mendelian diseases can be used as a baseline for efforts in this area. Data on the molecular nature and mechanisms of origin of spontaneous mutations underlying naturally occurring Mendelian diseases and on radiation-induced mutations in experimental systems suggest that for ionizing radiation, naturally occurring Mendelian diseases may not constitute an entirely adequate frame of reference and that current risk estimates for this class of diseases are conservative; these estimates however provide a margin of safety in formulating radiation protection guidelines. Currently available data on mechanisms and specificities of action of chemical mutagens, molecular dosimetry, repair of chemically induced adducts in the DNA, adduct-mutation relationships etc., permit the tentative conclusion that naturally occurring Mendelian diseases may provide a better baseline for genetic risk estimation for chemical mutagens than for ionizing radiation. With both ionizing radiation and chemical mutagens, the question of which Mendelian diseases are potentially inducible will become answerable in the near future when more molecular data on human genetic diseases become available. It is therefore essential that risk estimators keep abreast of advances in human genetics and integrate these into their conceptual framework. However, induced Mendelian diseases (especially the dominant ones which are of more immediate concern) are likely to represent a very small fraction of the adverse genetic effects of induced mutations. More attention therefore needs to be devoted to studies on the heterozygous effects of induced mutations. PMID:7506354

Sankaranarayanan, K

1994-01-01

386

Chemical flooding of oil reservoirs 2. Dissociative surfactant-polymer interaction with a negative effect on oil recovery  

Microsoft Academic Search

The presence of polymer and surfactant in injection water will improve the oil recovery during a water flood. The flooding method is termed low tension polymer water flood. During the flooding process both chemicals are present in the aqueous microemulsion phase. This paper gives a discussion of possible synergistic effects between the surfactant and the polymer in a dynamic flood

Tor Austad; Knut Taugbøl

1995-01-01

387

Early life stress, negative paternal relationships, and chemical intolerance in middle-aged women: support for a neural sensitization model.  

PubMed

This study (ntotal = 35) compared early life stress ratings, parental relationships, and health status, notably orthostatic blood pressures, of middle-aged women with low-level chemical intolerance (CI group) and depression, depressives without CI (DEP group), and normals. Environmental chemical intolerance is a symptom of several controversial conditions in which women are overrepresented, that is, sick building syndrome, multiple chemical sensitivity, chronic fatigue syndrome, and fibromyalgia. Previous investigators have postulated that people with CI have variants of somatization disorder, depression, posttraumatic stress disorder (PTSD) initiated by childhood abuse or a toxic exposure event. One neurobehavioral model for CI, somatization disorder, recurrent depression, and PTSD is neural sensitization, that is, the progressive amplification of host responses (e.g., behavioral, neurochemical) to repeated intermittent stimuli (e.g., drugs, chemicals, endogenous mediators, stressors). Females are more vulnerable to sensitization than are males. Limbic and mesolimbic pathways mediate central nervous system sensitization. Although both CI and DEP groups had high levels of life stress and past abuse, the CI group had the most distant and weak paternal relationships and highest limbic somatic dysfunction subscale scores. Only the CI group showed sensitization of sitting blood pressures over sessions. Together with prior evidence, these data are consistent with a neural sensitization model for CI in certain women. The findings may have implications for poorer long-term medical as well as neuropsychiatric health outcomes of a subset of women with CI. Subsequent research should test this model in specific clinical diagnostic groups with CI. PMID:9861591

Bell, I R; Baldwin, C M; Russek, L G; Schwartz, G E; Hardin, E E

1998-11-01

388

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

PubMed

A sensitive and specific liquid chromatography tandem mass spectrometric method was developed and validated for the simultaneous determination of rosuvastatin (ROS) and N-desmethyl rosuvastatin (NOR-ROS) in human plasma using deuterium-labeled internal standards. The plasma samples were prepared using liquid-liquid extraction with diethyl ether. Chromatographic separation was accomplished on an Xterra MS C18 column. The mobile phase consisted of a gradient mixture of 15?µmol/L ammonium acetate in water and in methanol, maintained at a flow rate of 0.4?mL/min. Mass spectrometric detection was carried out in negative electrospray ionization mode and monitored by quantification and qualification transitions for each analyte. Using 300 ?L plasma samples, the lower limits of quantification of ROS and NOR-ROS were 0.05 and 0.02?µg/L respectively. The linearity of ROS and NOR-ROS ranged from 0.05 to 42 and 0.02 to 14?µg/L respectively. The relative standard deviations of ROS and NOR-ROS were <13 and 9%, respectively, while the deviations from expected values were within -4.7-9.8 and -5.2-4.6%, respectively. The present method offered high sensitivity and was successfully applied to a 24?h pharmacokinetic study of ROS and NOR-ROS in healthy subjects receiving a single dose of 10?mg ROS. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23722358

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

2013-05-30

389

Oligomers, organosulfates, and nitrooxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2009-01-01

390

Oligomers, organosulfates, and nitroxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2008-01-01

391

Oligomers, organosulfates, and nitrooxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mecha- nism for atmospheric organic matter, and a potentially im- portant input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically char- acterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron reso- nance mass spectrometry (FT-ICR MS).

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2009-01-01

392

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

393

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

394

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

395

Screening for library-assisted identification and fully validated quantification of 22 beta-blockers in blood plasma by liquid chromatography–mass spectrometry with atmospheric pressure chemical ionization  

Microsoft Academic Search

A liquid chromatographic–mass spectrometric assay with atmospheric pressure chemical ionization (LC–APCI–MS) is presented for screening for, library-assisted identification (both in scan mode) and quantification (selected-ion mode) of the beta-blockers acebutolol, diacetolol, alprenolol, atenolol, betaxolol, bisoprolol, bupranolol, carazolol, carteolol, carvedilol, celiprolol, esmolol, labetalol, metoprolol, nadolol, nebivolol, oxprenolol, penbutolol, propranolol, sotalol, talinolol and timolol in blood plasma after mixed-mode (HCX) solid-phase extraction

Hans H. Maurer; Oliver Tenberken; Carsten Kratzsch; Armin A. Weber; Frank T. Peters

2004-01-01

396

Simultaneous determination by ultra-performance liquid chromatography–atmospheric pressure chemical ionization time-of-flight mass spectrometry of nitrated and oxygenated PAHs found in air and soot particles  

Microsoft Academic Search

An ultra-performance liquid chromatographic-atmospheric pressure chemical ionization time-of-flight mass spectrometric (UPLC-APCIToFMS)\\u000a method for rapid analysis of twelve nitrated polycyclic aromatic hydrocarbons (NPAHs) and nine oxygenated polycyclic aromatic\\u000a hydrocarbons (OPAHs) in particle samples has been developed. The extraction step using pressurized liquid extraction was optimized\\u000a by experimental design methods and the concentrated extracts were analyzed without further clean-up. Matrix effects resulting

Giovanni Mirivel; Véronique Riffault; Jean-Claude Galloo

2010-01-01

397

A Chemical Ionization High-Resolution Time-of-Flight Mass Spectrometer Coupled to a Micro Orifice Volatilization Impactor (MOVI-HRToF-CIMS) for Analysis of Gas and Particle-Phase Organic Species  

Microsoft Academic Search

We describe a new instrument, chemical ionization high-resolution time-of-flight mass spectrometer coupled to a micro-orifice volatilization impactor (MOVI-HRToF-CIMS). The MOVI-HRToF-CIMS instrument is unique in that, within a compact field-deployable package, it provides (1) quantifiable molecular-level information for both gas and particle phase organic species on timescales ranging from ?1 second for gases and 10 - 60 minutes for particle-phase compounds

Reddy L. N. Yatavelli; Felipe Lopez-Hilfiker; Julia D. Wargo; Joel R. Kimmel; Michael J. Cubison; Timothy H. Bertram; Jose L. Jimenez; Marc Gonin; Douglas R. Worsnop; Joel A. Thornton

2012-01-01

398

High-Throughput Walkthrough Detection Portal as a Measure for Counter Terrorism: Design of a Vapor Sampler for Detecting Triacetone Triperoxide Vapor by Atmospheric-Pressure Chemical-Ionization Ion-Trap Mass Spectrometry  

Microsoft Academic Search

Aiming to prevent terrorist attacks in places where many people are coming and going, we have been developing a “high-throughput detection portal system.” The portal system consists of a vapor sampler, an atmospheric-pressure chemical-ionization ion source, and an explosives detector based on ion-trap mass spectrometry. The vapor sampler was designed to be installed in an automated ticket gate of a

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

2012-01-01

399

Liquid Chromatography with Post-Column Reagent Addition of Ammonia in Methanol Coupled to Negative Ion Electrospray Ionization Tandem Mass Spectrometry for Determination of Phenoxyacid Herbicides and their Degradation Products in Surface Water  

PubMed Central

A new liquid chromatography (LC)-negative ion electrospray ionization (ESI?)–tandem mass spectrometry (MS/MS) method with post-column addition of ammonia in methanol has been developed for the analysis of acid herbicides: 2,4-dichlorophenoxy acetic acid, 4-chloro-o-tolyloxyacetic acid, 2-(2-methyl-4-chlorophenoxy)butyric acid, mecoprop, dichlorprop, 4-(2,4-dichlorophenoxy) butyric acid, 2,4,5-trichlorophenoxy propionic acid, dicamba and bromoxynil, along with their degradation products: 4-chloro-2-methylphenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol and 3,5-dibromo-4-hydroxybenzoic acid. The samples were extracted from the surface water matrix using solid-phase extraction (SPE) with a polymeric sorbent and analyzed with LC ESI? with selected reaction monitoring (SRM) using a three-point confirmation approach. Chromatography was performed on a Zorbax Eclipse XDB-C18 (50 × 4.6 mm i.d., 1.8 ?m) with a gradient elution using water-methanol with 2 mM ammonium acetate mobile phase at a flow rate of 0.15 mL/min. Ammonia in methanol (0.8 M) was added post-column at a flow rate of 0.05 mL/min to enhance ionization of the degradation products in the MS source. One SRM transition was used for quantitative analysis while the second SRM along with the ratio of SRM1/SRM2 within the relative standard deviation determined by standards for each individual pesticide and retention time match were used for confirmation. The standard deviation of ratio of SRM1/SRM2 obtained from standards run on the day of analysis for different phenoxyacid herbicides ranged from 3.9 to 18.5%. Limits of detection (LOD) were between 1 and 15 ng L?1 and method detection limits (MDL) with strict criteria requiring <25% deviation of peak area from best-fit line for both SRM1 and SRM2 ranged from 5 to 10 ng L?1 for acid ingredients (except dicamba at 30 ng L?1) and from 2 to 30 ng L?1 for degradation products. The SPE-LC-ESI? MS/MS method permitted low nanogram-per-liter determination of pesticides and degradation products for surface water samples.

Raina, Renata; Etter, Michele L.

2010-01-01

400

APPLICATION OF NEGATIVE ION CHEMICAL IONIZATION MASS SPECTROMETRY FOR THE ANALYSIS OF TRICHLOROPYRIDINOL IN SALIVA OF RATS EXPOSED TO CHLORPYRIFOS. (R828608)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

401

A comparison of Arctic BrO measurements by chemical ionization mass spectrometry and long path-differential optical absorption spectroscopy  

NASA Astrophysics Data System (ADS)

A measurement intensive was carried out in Barrow, Alaska, in spring 2009 as part of the Ocean-Atmosphere-Sea-Ice-Snowpack (OASIS) program. The central focus of this campaign was the role of halogen chemistry in the Arctic. A chemical ionization mass spectrometer (CIMS) performed in situ bromine oxide (BrO) measurements. In addition, a long path-differential optical absorption spectrometer (LP-DOAS) measured the average concentration of BrO along light paths of either 7.2 or 2.1 km. A comparison of the 1 min observations from both instruments is presented in this work. The two measurements were highly correlated and agreed within their uncertainties (R2 = 0.74, slope = 1.10, and intercept = -0.15 pptv). Better correlation was found (R2 = 0.85, slope = 1.04, and intercept = -0.11 pptv) for BrO observations at moderate wind speeds (>3 m s-1 and <8 m s-1) and low nitric oxide (NO) mixing ratios (<100 pptv). The improved agreement is likely due to the elimination of periods when the spatial distribution of BrO is inhomogeneous. The detection limit obtained for the CIMS was 2.6 pptv (3?) for a 4 s integration period, and the estimated uncertainty was ˜30%. The detection limits for the LP-DOAS ranged from 0.7 to 5 pptv (3?) depending on the level of ambient light and the chosen light path, and the estimated systematic error was 10%. The agreement between the CIMS and LP-DOAS is excellent and demonstrates the capability of both instruments to selectively and accurately measure BrO with high sensitivity.

Liao, J.; Sihler, H.; Huey, L. G.; Neuman, J. A.; Tanner, D. J.; Friess, U.; Platt, U.; Flocke, F. M.; Orlando, J. J.; Shepson, P. B.; Beine, H. J.; Weinheimer, A. J.; Sjostedt, S. J.; Nowak, J. B.; Knapp, D. J.; Staebler, R. M.; Zheng, W.; Sander, R.; Hall, S. R.; Ullmann, K.

2011-07-01

402

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.

Bedner, Mary; Phinney, Karen W.

2012-01-01

403

(+)-Silybin, a pharmacologically active constituent of Silybum marianum: fragmentation studies by atmospheric pressure chemical ionization quadrupole time-of-flight tandem mass spectrometry.  

PubMed

The fragmentation behavior of (+)-silybin (1) and (+)-deuterosilybin (2), as well as of their flavanone-3-ol-type building blocks, such as 3,5,7-trihydroxy-2-phenyl-4-chromanone (3) and 2-(1,4-benzodioxolanyl)-3,5,7-trihydroxy-4-chromanone (4), were investigated by atmospheric pressure chemical ionization quadropole time-of-flight tandem mass spectrometry in the positive ion mode (APCI(+)-QqTOF MS/MS). The product ion spectra of the protonated molecules of 1 revealed a rather complicated fragmentation pattern with product ions originating from consecutive and competitive loss of small molecules such as H2O, CO, CH2O, CH3OH and 2-methoxyphenol, along with the A+- and B+-type ions arising from the cleavage of the C-ring of the flavanone-3-ol moiety. The elucidation of the fragmentation behavior of 1 was facilitated by acquiring information on the fragmentation characteristics of the flavanone-3-ol moieties and 2. The capability of the accurate mass measurement on the quadrupole time-of-flight mass spectrometer allowed us to determine the elemental composition of each major product ion. Second-generation product ion spectra obtained by combination of in-source collision induced dissociation (CID) with selective CID (pseudo-MS(3)) was also helpful in elaborating the fragmentation pathways and mechanism. Based on the experimental results, a fragmentation mechanism as well as fragmentation pathways for 1 and its flavanone-3-ol building blocks (3, 4) are proposed and discussed. PMID:17569099

Kéki, Sándor; Tóth, Katalin; Zsuga, Miklós; Ferenczi, Renáta; Antus, Sándor

2007-01-01

404

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

405

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

PubMed Central

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

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

2013-01-01

406

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

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; Richter, Sandra S

2012-04-11

407

Thermochemistry of organic and heteroorganic species. Part XIX. Structural aspects and thermochemical approach to isomerization and fragmentation of negative ions: Skeletal rearrangements, molecular ion and artifacts  

Microsoft Academic Search

Many hundreds of isomerization and fragmentation processes for negatively charged ions obtained in electron attachment dissociation, collision induced dissociation and negative chemical ionization have been analyzed to find out certain regularities in gas-phase monomolecular chemistry of negative ions like it was earlier performed for positive ions (Eur.J.Mass Spectrom., 8 (2002) 409). This analysis combined with systematic application of the data

Dmitry Ponomarev; Viatcheslav Takhistov

2006-01-01

408

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)

1996-09-12

409

IONIZATION CHAMBER  

DOEpatents

This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

Redman, W.C.; Shonka, F.R.

1958-02-18

410

Online profiling of triacylglycerols in plant oils by two-dimensional liquid chromatography using a single column coupled with atmospheric pressure chemical ionization mass spectrometry.  

PubMed

The complexity of natural triacylglycerols (TAGs) in various edible oils is high because of the hundreds of TAG compositions, which makes the profiling of TAGs quite difficult. In this investigation, a rapid and high-throughput method for online profiling of TAGs in plant oils by two-dimensional (2D) liquid chromatography using a single column coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry was reported. A novel mixed-mode 2D chromatographic column packed with silver-ion-modified octyl and sulfonic co-bonded silica was employed in this online 2D separation system. This novel 2D column combined the features of C8 column and silver-ion. In comparison with the traditional C18 column and silver-ion column, which are the two main columns used for the separation of complex TAGs in natural oil samples, this novel 2D column, could provide hydrophobic interactions as well as ?-complexation interactions. It exhibited much higher selectivity for the separation of TAGs, and the separation was rapid. This online 2D separation system was successful in the separation of a large number of TAG solutes, and the TAG structures were evaluated by analyzing their APCI mass spectra information. This system was applied for the profiling of TAGs in peanut oils, corn oils, and soybean oils. 30 TAGs in peanut oils, 18 TAGs in corn oils, and 21 TAGs in soybean oils were determined and quantified. The highest relative content of TAGs was LLL, which was found in corn oil with the relative content up to 45.43 (%, w/w), and the lowest relative content of TAGs was LLS and OSS, which was found in soybean oil and corn oil respectively, with the relative content only 0.01 (%, w/w). In addition, the TAG data were analyzed by principal component analysis (PCA). Results of PCA enabled a clear identification of different plant oils. This method provided an efficient and convenient chromatographic technology for the fast characterization and quantification of complex TAGs in plant oils at high selectivity. It has great potential as a routine analytical method for analysis of edible oil quality and authenticity control. PMID:24034135

Wei, Fang; Ji, Shu-Xian; Hu, Na; Lv, Xin; Dong, Xu-Yan; Feng, Yu-Qi; Chen, Hong

2013-09-05

411

Quantitative determination of perfluorooctanoic acid ammonium salt in human serum by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.  

PubMed

A sensitive, specific, accurate and reproducible analytical method was developed and validated to quantify perfluorooctanoic acid (PFOA) in human serum. After initial extraction with an ion-paring reagent, the procedure for quantifying PFOA is based on high-performance liquid chromatography (HPLC) interfaced to negative ion tandem mass spectrometry, operating in selected ion monitoring mode. The retention times of PFOA and its internal standard (D,L-malic acid) were 5.85 and 1.70 min, respectively. The assay was linear over the range 0-500 ng/mL, with a lower limit of quantification (LOQ) of 25 ng/mL, and with a coefficient of variation (CV) of 7.3%. The lower limit of detection (LOD) was assessed as 10 ng/mL. The overall precision and accuracy were assessed on three different d