Showing papers on "Atmospheric-pressure chemical ionization published in 1977"
70 citations
57 citations
42 citations
TL;DR: The novel aspects of atmospheric pressure ionization mass spectrometry lie in its versatility and high sensitivity of detection.
Abstract: Contemporary analytical systems based on mass spectrometry include as components a gas chromatograph, a mass spectrometer, and a computer. The form of operation is usually in electron impact ionization mode for identification and structural studies, and in chemical ionization mode for quantitative analyses. Important stages in the development of these systems included the design of "molecule separators" for the concentration of solutes in the gas phase, the use of mass spectrometers as specific ion detectors, the introduction of chemical ionization techniques, and the development of computer-based operation, data acquisition, and data analysis capabilities. A current line of investigation is concerned with the design and use of systems based on atmospheric pressure ionization. Samples are ionized in a small reaction chamber external to the low-pressure region of a quadrupole mass analyzer. The primary source of electrons is a 63Ni foil or a corona discharge. The ionization process leading to positive ions involves a sequence of ion molecule reactions, usually electrons leads to carrier gas ions leads to reagent ions leads to sample component ions. Negative ions may be formed by direct electron attachment, or by ion molecule reactions that include new types of elimination reactions. The source will accept a variety of gases and solvents. The sample may be introduced in the gas phase without solvents, by probe injection, or in the effluent stream from a gas chromatograph. Samples may be introduced in the liquid phase in solvents by injection after the fashion of gas chromatography or in the effluent stream from a high-performance liquid chromatograph. The novel aspects of atmospheric pressure ionization mass spectrometry lie in its versatility and high sensitivity of detection. Few clinical chemistry laboratories now use these systems. Significant future uses are likely to be in analytical work involving therapeutic drug monitoring and studies of drug metabolism, and in analyses for environmental biohazards including pesticides, herbicides, polyhalobiphenyls, dibenzodioxins, and other toxic compounds.
40 citations
TL;DR: The need for independent dual detection in the analysis of complex mixtures by gas chromatography-chemical-ionization mass spectrometry is illustrated in this paper, where the authors show how to calibrate both the flame ionization detection and total ion current records in spectrum index numbers through the use of an event marker, triggered by the data system.
36 citations
33 citations
30 citations
TL;DR: Hexakis (multifluoroalkoxy)cyclotriphosphazenes satisfy a growing need for high molecular weight reference compounds amenable to either electron impact or field ionization, and offer greater volatility, easier synthesis and better mass spectral characteristics.
Abstract: Because of poor field ionization sensitivity or an insufficient number of peaks, conventional reference materials are inadequate for field desorption mass spectrometry. Hexakis (multifluoroalkoxy)cyclotriphosphazenes satisfy a growing need for high molecular weight reference compounds amenable to either electron impact or field ionization. In comparison with tris(perfluoroalkyl)-s-triazine standards, the substituted phosphazenes offer greater volatility, easier synthesis and better mass spectral characteristics. Phosphazene mixtures, in particular, cover a broad mass range in either ionization mode, creating new measurement capabilities for ions at high masses.
26 citations
TL;DR: In this paper, a thermobalance and a quadrupole mass spectrometer with chemical ionization (CI) was used to investigate thermal decomposition reaction under normal pressure most efficiently.
26 citations
TL;DR: In this article, a simple and inexpensive ion source was developed for collision dynamic studies, where negative halogen ions were produced by negative surface ionization at a hot surface of LaB6.
Abstract: A simple and inexpensive ion source has been developed for collision dynamic studies. The negative halogen ions are produced by negative surface ionization at a hot surface of LaB6. Because of the selectivity of this ionization process mass selection is not necessary. Emission densities of 10−4 A/cm2 at an energy spread of 0.55 eV are obtained.
TL;DR: Metastable peaks have been observed from the unimolecular decomposition of an excited intermediate ion formed by ion-molecule reaction in a high-pressure chemical ionization source.
TL;DR: In this paper, a correlation has been found between the stereochemistry of 3-methoxyeyclopentyl and 3methoxyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MHCH3OH]+ ions are more abundant for the trans isomers.
Abstract: A correlation has been fround between the stereochemistry of 3-methoxyeyclopentyl and 3-methoxyccyelohexyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MHCH3OH]+ ions are more abundant for the trans isomers. A similar situation occurs in the iow temperature methane chemical ionization spectra of the coresponding trimethylsilylethers.
TL;DR: The diastereomeric hydroxyamines, ephedrine and psi-ephedrine, were well differentiated by gas chromatography of their N-acetyl O-trimethylsilyl derivatives, and under chemical ionization conditions (isobutane) abundant protonated molecular ions were produced.
Abstract: The diastereomeric hydroxyamines, ephedrine and psi-ephedrine, were well differentiated by gas chromatography of their N-acetyl O-trimethylsilyl derivatives. For the analytical separation of enantiomers, conversion into N-(R)-alpha-phenylbutyryl O-trimethylsilyl derivatives was effective in the cases of ephedrine, psi-ephedrine and nor-psi-ephedrine (but not that of nor-ephedrine, on the two stationary phases used). Electron impact mass spectra showed structurally diagnostic fragmentations, but the two diastereomeric amides from each pair of enantiomers yielded generally similar spectra. Molecular ions were of low abundance, but under chemical ionization conditions (isobutane) abundant protonated molecular ions were produced.
TL;DR: The five major alkaloids of opium -morphine, narcotine, codeine, thebaine and papaverine - have been identified by the chemical ionization (CI) mass spectrum of opium, without any prior separation as discussed by the authors.
Abstract: The five major alkaloids of opium - morphine, narcotine, codeine, thebaine and papaverine - have been identified by the chemical ionization (CI) mass spectrum of opium, without any prior separation. CI reagents used were isobutane, at a pressure of 0.2–0.5 Torr and water at a pressure of 0.05 – 0.07 Torr. Source temperatures were in the range of 155–200°C and probe temperatures in the range of 90–160°C. The base peak in the CI spectrum of opium is at m/e 220, resulting from an unusual cleavage of the MH ion of narcotine.
TL;DR: Twenty-nine derivatives of phenothiazine formed relatively stable ions by proton capture under conditions of chemical ionization, using methane or isobutane as reagent gas.
TL;DR: Pyrethrins, the 6 naturally occurring insecticidal esters of pyrethrum extract, were analyzed by combined gas-liquid chromatography-chemical ionization mass spectrometry and a lower limit of detectability of all 6 esters was 114 ng of total extract injected on the column.
Abstract: Pyrethrins, the 6 naturally occurring insecticidal esters of pyrethrum extract, were analyzed by combined gas-liquid chromatography-chemical ionization mass spectrometry. Separation was best on an OV-25 column with temperature programming; The chemical ionization mass spectra for the 6 esters as well as for the thermally isomerized pyrethrins I and II are reported and discussed. Using selective ion monitoring, a lower limit of detectability of all 6 esters was 114 ng of total extract injected on the column.
TL;DR: The mass spectra of some butyrophenones are presented and the chemical ionization spectra show the quasi molecular ion (M + H)+ to be the most abundant ion.
Abstract: The mass spectra of some butyrophenones are presented. Electron impact ionization and chemical ionization with isobutane as the reagent gas are compared. The chemical ionization spectra show the quasi molecular ion (M + H)+ to be the most abundant ion. Important fragments in the electron impact spectra are discussed for easy determination of other similar compounds.
TL;DR: The chemical ionization mass spectra of ten compounds of the group of natural monohydroxy and monoacyloxy derivatives of dihydropyranocoumarins and dihydrofurocoumarin have been studied in this paper.
Abstract: The chemical ionization mass spectra of ten compounds of the group of natural monohydroxy and monoacyloxy derivatives of dihydropyranocoumarins and dihydrofurocoumarins have been studied. Their difference from the electron impact mass spectra has been shown. The structural-analytical possibilities of the method of chemical ionization for this series of substances has been determined.