Showing papers on "Atmospheric-pressure chemical ionization published in 1979"
TL;DR: The application of gas chromatography and chemical ionization mass spectrometers to the determination of a variety of alkyl alkyls alklphosphonates, phosphonofluoridates, and an amidophosphorocyanidate is described in this paper.
Abstract: The application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]+ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.
89 citations
TL;DR: A new technique resulting in the direct, instantaneous analyses of trace compounds in breath appears to be of potential value in routine detection and treatment of hyperammonemia patients and a number of diagnostic research applications.
Abstract: A new technique is reported resulting in the direct, instantaneous analyses of trace compounds in breath. The analyses were performed using a commercial atmospheric pressure chemical ionization mass spectrometer (TAGA TM2000 APCI mass spectrometer). A known flow of breath sample is introduced into the ionization region of the mass spectrometer. The study includes the measurement and monitoring in real-time, of breath ammonia during a 24 hour and a 48 hour period. The ammonia profiles indicate a personalized daily pattern associated with each subject. This method appears to be of potential value in routine detection and treatment of hyperammonemia patients. Results also show that it is possible to obtain instantaneous analyses of several naturally occurring metabolites and other substances on breath in the ppm to ppt range, suggesting a number of diagnostic research applications.
62 citations
54 citations
TL;DR: The negative ion chemical ionization mass spectra of polychlorinated dibenzo-p-dioxins using oxygen, methane and methane/oxygen were reported in this article.
Abstract: The negative ion chemical ionization mass spectra of polychlorinated dibenzo-p-dioxins using oxygen, methane and methane/oxygen are reported together with their methane positive ion chemical ionization mass spectra and conventional electron impact spectra. The methane/oxygen negative ion chemical ionization mass spectra proved to be the most useful of the negative ion spectra for structure determination.
52 citations
TL;DR: The previously reported gas chromatographic--mass spectrometric assay for clonazepam using positive ion chemical ionization has been modified to employ negative ion chemical ions, which is approximately twenty times better than the positive ionchemical ionization procedure with similar precision.
40 citations
40 citations
34 citations
TL;DR: In this article, the relative protonation cross-sections of β-amino alcohols appear to be independent of their relative affinities, and the interfunctional distance between functional groups is not a significant determinant of dehydration.
Abstract: Dehydration of β-amino alcohols after chemical ionization with iso-butane as reagent gas is dependent upon the interfunctional distance. Relative protonation cross-sections of both functional groups appear to be essentially independent of their relative proton affinities.
34 citations
30 citations
TL;DR: In this paper, multiphoton ionization spectroscopy has been used to measure ionization threshold for pyrrole and it has been shown that the threshold is independent of the pyroxide concentration.
Abstract: Multiphoton ionization spectroscopy has been used to measure ionization threshold for pyrrole.(AIP)
27 citations
TL;DR: The position of the triple bond of n-alkynes can be determined by the analysis of the relative abundance of the CnH2n−1 ions in the chemical ionization (i-butane) spectra as mentioned in this paper.
Abstract: The position of the triple bond of n-alkynes can be determined by the analysis of the relative abundance of the CnH2n−1 ions in the chemical ionization (i-butane) spectra. However, chemical ionization (NO) spectra where both hydrocarbon and NO-containing ions are formed in a characteristic manner are more reliable for this purpose. The limitations of the fragmentation rules established earlier for electron impact spectra of alkynes were investigated by examination of additional examples.
TL;DR: In this paper, a pyrolysis/mass spectrometric study on polystyrene, polyvinyl chloride, and poly(methyl methacrylate) with electron ionization and chemical ionization (CI) mass spectrometers is presented.
Abstract: Pyrolysis/mass spectrometric studies have been made on polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) with electron ionization (EI) and chemical ionization (CI) mass spectrometry and a variable temperature probe for direct insertion into the source of the mass spectrometer. Similar results obtained with EI and CI mass spectrometry are in agreement with previous experiments. Advantages of the simplification of spectra in the CI made, as well as the advantages of using both techniques for identification of pyrolysis products, are discussed.
TL;DR: In this paper, a new vacuum atomizing sample introduction device was developed and applied to take stable and reproducible chemical ionization mass spectra of various involatile compounds, such as free amino acids, drug components in a cold medicine, higher phthalates, oligomers of styrene and ethyleneglycol, etc.
Abstract: A new vacuum atomizing sample introduction device was developed and applied to take stable and reproducible chemical ionization mass spectra of various involatile compounds. As examples, chemical ionization spectra of some free amino acids, drug components in a cold medicine, higher phthalates, oligomers of styrene and ethyleneglycol, etc., are presented.
TL;DR: By using selected ion monitoring in the chemical ionization mode, the authors have been able to quantitate the endogenous concentrations of phenylethylamine and phenylethanolamine in rat brain.
TL;DR: In this paper, the best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS-25 mass spectrometer.
Abstract: The best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS-25 mass spectrometer. The best reagent gas pressure is shown to be different for each gas and is significantly lower than is usually reported in the literature.
TL;DR: A new gas chromatographic mass spectrometric chemical ionization assay for haloperidol with selectedion monitoring is presented which provides for better combined selectivity and sensitivity than previous assays.
Abstract: A new gas chromatographic mass spectrometric chemical ionization assay for haloperidol with selectedion monitoring is presented which provides for better combined selectivity and sensitivity than previous assays. Levels of haloperidol in 2 ml of human plasma were reproducibly measured down to subnanogram levels. Both methane and methane--ammonia chemical ionization spectra are presented for haloperidol and the internal standard trifluperidol.
TL;DR: After appropriate sample pretreatment and derivatization, uremic serum was investigated by combined high resolution gas chromatography and mass spectrometry, using both electron impact and chemical ionization methods, showing protonated molecular ions, whereas aldoses did not.
Abstract: After appropriate sample pretreatment and derivatization, uremic serum was investigated by combined high resolution gas chromatography and mass spectrometry, using both electron impact and chemical ionization methods. Electron impact and chemical ionization spectra of a number of identified (trimethylsilylated) carbohydrates and organic acids are compared. The utilization of chemical ionization mass spectrometry, with isobutane as the reagent gas, is discussed in detail. The influence of the reagent gas pressure on the total ion current and on the spectral appearance was studied. The identification of compounds, based on electron impact mass spectral data, was confirmed and often aided appreciably by using this technique. The chemical ionization spectra of trimethylsilylated alditols and aldonic acids, as well as of other organic acids showed protonated molecular ions, whereas aldoses did not. Differences with electron impact spectra are found mainly in the high mass region. The loss of one or more trimethylsilanol groups becomes the predominating fragmentation route at higher reagent gas pressure.
TL;DR: In this article, a modification or chemical ionization mass spectrometry, which involves photoionization and cyclohexane as the source of the reagent ion, has been used to develop a technique for discriminatory fingerprinting of neat liquid fossil fuels.
Abstract: A modification or chemical ionization mass spectrometry, which involves photoionization and cyclohexane as the source of the reagent ion, has been used to develop a technique for discriminatory fingerprinting of neat liquid fossil fuels. The method provides a 2-min turn-around time between samples and batch introduction, with no requirements for prior separation or fractionation. Depending upon the conditions chosen, the technique may also be extended to the partial quantification of aromatic and olefinic sample components. 9 figures.
TL;DR: The intensity of the molecular weight-determining ions relative to that of the ion that characterizes the N -terminal residue (β-cleavage ion) is greater in the CI mode than in the EI mode, which will extend the lower limit for Me 3 Si dipeptide identification.
TL;DR: A gas chromatographic chemical ionization mass spectrometric assay has been developed to measure carprofen in blood that features the addition of either a structural or stable isotope analog internal standard to plasma prior to a simple benzene extraction.
Abstract: A gas chromatographic chemical ionization mass spectrometric assay has been developed to measure carprofen in blood. The method features the addition of either a structural or stable isotope analog internal standard to plasma prior to a simple benzene extraction at pH 4.5. The residue, after removal of the benzene, is methylated with ethereal diazomethane. Following evaporation of the methylating solvents, a portion of the reconstituted residue is analyzed by gas chromatography mass spectrometry. The mass spectrometer is set to monitor in the gas chromatographic effluent the [MH]+ ions of carprofen methyl ester and the methyl ester of the internal standard generated by isobutane chemical ionization. Assay sensitivity is 5 pmol ml-1. When 200 pmol ml-1 samples are analyzed using a stable isotope analog as the internal standard, the precision and accuracy are both 4%. Using a structural analog as the internal standard, the assay was neither as precise nor as accurate.
TL;DR: A method for the estimation of sphingolipids based on the quantitation, by gas-liquid chromatography/chemical ionization, of the long-chain aldehydes released from the native lipids, is described.
TL;DR: In this article, chemical ionization induced fragmentations (with 2-methylpropane as reagent gas) of 4-methyl- and 4-5-dimethyl-2-phenyl-1,3,2-dioxaborolane gave in each case two fragments, a hydrocarbon ion and metaboric acid.
Abstract: Chemical ionization induced fragmentations (with 2-methylpropane as reagent gas) of 4-methyl- and 4,5-dimethyl-2-phenyl-1,3,2-dioxaborolane and 4-methyl-2-phenyl-1,3,2-dioxaborinane gave in each case two fragments, a hydrocarbon ion and metaboric acid. Propeae and thence metaboric acid are eliminated from 4,6-dimethyl-2-phenyl-1,3,2-dioxaborinane. The mechanisms of the fragmentations are discussed. Under the conditions used 2-phenyl-1,3,2-dioxaborolane and 2-phenyl-1,3,2-dioxaborinane do not fragment.
TL;DR: The negative ion mass spectra, which indicate the position of the double bonds in hydrocarbon radicals, supplement the mass-spectral data obtained by surface ionization and electron impact.
Abstract: 1.
Comparison of different ionization modes (surface, electron impact, dissociative electron capture) from the point of view of informative value of the derived data about the structure of N-alkenyl-, N-alkadienyl-, and N-cycloalkenyl-N-substituted cyclic amines showed that none of these ionization modes has a particular advantage.
2.
The negative-ion mass spectra, which indicate the position of the double bonds in hydrocarbon radicals, supplement the mass-spectral data obtained by surface ionization and electron impact. Thus the combined utilization of these methods enables structural isomers to be identified.