Low-voltage Mass Spectrometry Research Articles

Polycyclic aromatic structure distributions by high-resolution mass spectrometry

Detailed analytical description of the polycyclic aromatic structure distribution is useful for assessing the exact effects of refining processes, such as solvent extraction and hydrotreating, that alter or remove these compounds. High-resolution, low-voltage mass spectrometry was used to characterize the clay gel aromatics fractions of a petroleum vacuum distillate and three lubricant base oils that are derived from it. Proprietary methods were used to extract and hydrotreat the distillate, and different levels of severity were employed

Modeling and predicting the composition of fossil fuel-derived pyrolysis liquids using low-voltage mass spectrometry and canonical correlation analysis

Low-voltage electron ionization mass spectrometry was performed on 25 fossil fuel samples (21 coals, 2 oil shales, 1 tar sand, and 1 coal resin concentrate) and their respective pyrolysis liquids by means of a fixed-bed reactor. By using principal component analysis, the tar evaporation spectra and the solid fuel pyrolysis spectra were classified in terms of the underlying structural variables. It was demonstrated that the canonical variate model enabled predcition of the mass spectrum of a given coal tar sample from the measured pyrolysis mass spectrum of the corresponding coal sample. Agreement with the experimental results was reasonably good

Selective isolation of carbazoles from crude oil

1. 1. A procedure has been developed for selective and complete isolation of carbazoles from residue (> 250°C) of Samotlor crude oil by means of adsorption chromatography on silica gel. 2. 2. Impurities of other types of petroleum compound were not found by IR spectroscopy and low-voltage mass spectrometry in isolated carbozole specimens.

Correlation of nitroaromatic compounds with the mutagenic activity of coal fly ash.

Stack-collected fly-ash particles from a commercial pulverized-coal power plant were extracted with 60/40 w/w benzene-methanol to remove as much of the organic fraction as possible. The extract was sequentially fractionated on a series of high-performance liquid chromatography columns, and the Salmonella bacterial mutagenicity assay using both normal and nitroreductase-deficient strains was used to localize the most mutagenic fractions. Selected fractions were analyzed by a variety of techniques, including gas chromatography with dual-flame ionization and thermionic nitrogen-phosphorus detectors, gas chromatography-mass spectrometry, direct-probe low-resolution or low-voltage mass spectrometry, and high-resolution mass spectrometry. Mutagenicity data indicated that nitroorganic compounds were the primary mutagens in all samples submitted for chemical analysis. A series of homologous alkylated nitrophenanthrenes appear to be important mutagens in one major fraction, while alkylated nitrofluorenones appear to be the dominant mutagens in a second major fraction. No nitro compounds were identified in a third major fraction. In addition to the nitro compounds, substantial amounts of fluorenones were also found, although these are not believed to contribute to the direct-acting mutagenic activity of the samples.

Characterization scheme of nitrogen bases in coal-derived liquids

A method has been developed for the characterization of basic nitrogen aromatic compounds in coal-derived liquids. The basic fraction extracted by a chromatographic separation was analysed by low-voltage mass spectrometry and semiquantitative data were obtained.

Gas chromatographic mass spectrometric determination of high-molecular-weight polycyclic aromatic hydrocarbons in coal tar

High-molecular-weight (MW 300-456) polycyclic aromatic hydrocarbons (PAH) were extracted from coal tar and isolated by a separation scheme involving column chromatography on silica gel and Sephadex LH-20. The PAH fractions obtained by this procedure were investigated by low-voltage mass spectrometry; separated by capillary gas chromatography and characterised by capillary gas chromatography/mass spectrometry.

Mass spectroscopic characterization of tars from the gasification of low-rank coals

Mass spectroscopic methods were developed for characterization of gasifier tars. The tars studied were produced during pilot plant operation of the GFETC slagging fixed-bed gasifier. Nine samples were selected, representing four low-rank coals and a range of gasifier conditions. The tars were analysed by gas chromatography-mass spectrometry, high-resolution mass spectrometry, and low-voltage mass spectrometry. Whole samples and fractions separated by column chromatography were analysed by conventional g.c.-m.s. techniques for identification of major compounds. Carbon number analysis was accomplished using h.r.m.s. for mass identification and l.v.m.s. for quantitative analysis. The chemical nature of the coal gasified was shown to be important in determining the composition of the tar. Approximately twenty constituents varied markedly in tars produced from different coals gasified under identical conditions. The important operating parameters affecting tar composition are the amount of hydrogen in the gas phase and the coal residence time. Neither operating pressure nor oxygen rate appear to be related to the composition of the tar.

Ammoxidation of α-methylstyrene to atroponitrile over U-Sb-oxide catalysts

Atroponitrile (α-phenylacrylonitrile) can be synthesized by the direct catalytic ammoxidation of α-methylstyrene. Conversions to atroponitrile of 57% per pass with a selectivity of 85% are attained using a Nb-promoted USb 4.6O 13.2 catalyst. Several other USboxide catalysts give similar results. A detailed study of reaction variables shows that an optimal yield of atroponitrile is formed under conditions of short contact times (0.5 sec), low surface area (7 m 2/g), low feed: air + diluent ratio ( 1 120 ), and N 2 dilution. The structure of the major product of α-methylstyrene ammoxidation has been unambiguously determined as α-phenylacrylonitrile by ir, NMR, and low-voltage mass spectrometry. Atroponitrile dimerizes to 1,4-dicyano-1-phenyl-1,2,3,4-tetrahydronaphthalene (DPT) in benzene solution with second-order kinetics and an E a of 14.8 kcal/mole, typical of other Diels-Alder reactions. The dimer exists in both crystalline and amorphous forms. The rate of cinnamonitrile formation from ammoxidation of allylbenzene is 2.9 times faster than from β-methylstyrene, suggesting that the ammoxidation of aromatic olefins proceeds through a common allylic intermediate.

Pyrolysis mass spectra, sulfhydryl and tryptophan content of the embryonic nuclei from adult human normal and nuclear-cataractous lenses

Cataractous state-related alterations were studied by Curie-point pyrolysis low voltage mass spectrometry performed on the embryonic nuclei from adult normal and nuclear-cataractous human lenses. It was shown that the relative intensities of ion signals assigned to sulfur dioxide and, tentatively, to other sulfur oxidation products correlate with the increase in lens nuclear color. Since these ion signals may represent pyrolysis fragments from methionine sulfoxide, methionine sulfone, cysteic acid and disulfide compounds present in the parent material, it is concluded that progressive oxidation of sulfur compounds appears to take place during nuclear cataractogenesis. Automated pyrolysis mass spectrometry coupled with multivariate analysis of the spectral data by computer turned out to be a rapid method of characterizing submilligram samples of lens material. The results were supported by data obtained by conventional determination of sulfhydryl and tryptophan groups.

The application of low voltge mass spectrometry to the determination of extent and location of deuterium substitution in dethiobiotin.

The fragmentation mechanism of dethiobiotin and its derivatives has been studied. A new fragmentation favoured at low energy allows the localization of deuterium on the carbons 2, 3, 4 and 5 in a sample of monodeuterated dethiobiotin.

Characterization of Neisseria meningitidis capsular polysaccharides containing sialic acid by pyrolysis mass spectrometry

The group B, C, W-135, and Y capsular polysaccharides of Neisseria meningitidis which contain sialic acid were differentiated by Curie-point pyrolysis low-voltage mass spectrometry. A large series of partially purified group B polysaccharide preparations obtained from pathogenic as well as nonpathogenic strains were analyzed by the same technique. It was shown that the carbohydrate structure of these group B polysaccharides appears to be the same throughout the whole series. Slight immunogenicity of some of the group B polysaccharide preparations tested is probably due to protein impurities. Automated pyrolysis mass spectrometry coupled with multivariate analysis of the spectral data by computer turns out to be a rapid method of characterizing microgram samples of large series of polysaccharide preparations.

Mass spectrometry of biologically active substances

The mass spectra of 2- and 4-iminobarbituric acid derivatives were studied in relation to the mass spectra of their oxygen analogs. It is shown that the pathways of fragmentation of the investigated compounds depend on the type of substituent attached to the C5 atom, the position of the imino and oxo groups in the ring, and the specific mass-spectral properties. The fragmentation was studied by means of low-voltage mass spectrometry and deuterium labeling.

Effect of solvent on molecular composition in coal liquefaction

The product from uncatalysed liquefaction of lignite using synthesis gas (CO-Steam process) was examined by column chromatography, high-resolution mass spectrometry, gas chromatography-mass spectrometry, and low-voltage mass spectrometry. The nature of the vehicle solvent affected the type and distribution of compounds in the product oil. Anthracene oil and recycle oil as solvents gave mainly aromatics and phenols. When tetralin was used as solvent, the product showed larger amounts of oxygen compounds, more hydroaromatic compounds, and a greater degree of alkylation in high-molecular-weight aromatics. Tetralin, therefore, appears to be a more powerful hydrogen donor than anthracene oil or recycle oil in stabilizing intermediate fragments that would otherwise repolymerize. Carbon-number analysis data for liquids prepared using three different solvents are presented.

Nitrogen compounds in coal derived liquids

Five liquid products from different pilot plant scale coal liquefaction processes were examined. Column chromatography was used to isolate a fraction of each sample that contained the nitrogen compounds, and this fraction was subjected to gas chromatography-mass spectrometry (GC/MS), low voltage mass spectrometry, and high resolution mass spectrometry. The major compound types seen were quinolines, benzoquinolines, and carbazoles. Benzocarbazoles and compounds in the mass Z series -13 N (phenylpyridines, diphenylamines, and aminobiphenyls) were also major constituents in some liquids studied. The composition of the liquids reflected differences in process conditions. A broader range of compounds resulted from more vigorous liquefaction conditions (higher pressure, higher temperature, longer reaction time, or recycle).

Preparation and low-voltage mass spectrometry sensitivities of methylated polynuclear aromatic hydrocarbons

The composition of the oil produced by the CO-Steam Process is being studied in detail using mass spectrometry as the primary method. (LK)

Application of low-voltage mass spectrometry to detect the metabolic products of drugs

Application of low-voltage mass spectrometry to detect the metabolic products of drugs

Note on the application of low voltage mass spectrometry to stereochemical problems

AbstractUsing the stereoisomeric 1,2‐dimethyl‐4‐alkyldecahydroquinol‐4‐ols and various examples described elsewhere it was shown that there are many cases when decreasing of the electron energy does not lead to an increase in the quantitative differences between the mass spectra of stereoisomers.

Studies on the structure and origin of soil humic acids by curie point pyrolysis in direct combination with low-voltage mass spectrometry

Curie point pyrolysis in combination with low voltage mass spectrometry has shown that humic acids extracted from three typical Indian soils have similar structures which resemble that of a fungal ‘humic acid’ rather than that of a lignin.

Mass spectrometry of indole compounds (review)

The behavior of the simplest indole systems upon electron impact is examined. The rearrangements occurring during the first stages of the disintegration are discussed, and the effect of these processes on dissociative ionization is demonstrated. The possible disintegration mechanisms were confirmed in a number of cases by investigation of labeled compounds and by the application of high-resolution mass spectrometry, kinetic methods, and low-voltage mass spectrometry.

Determination of Mercaptans in Naphthas by Low Voltage Mass Spectrometry

Determination of Mercaptans in Naphthas by Low Voltage Mass Spectrometry