Chromatography-electron Impact Mass Spectrometry Research Articles

A selected ion monitoring method for environmental contaminants. 1—hexachlorocyclohexane isomers in an aquatic environment

The analytical methodology of 1,2,3,4,5,6-hexachlorocyclohexane isomers residing in an aquatic environment was investigated with gas chromatography electron impact mass spectrometry selected ion monitoring as the determinative technique. An extraction method with a macroreticular Amberlite XAD-2 resin column was successfully developed and the extract was subjected to the gas chromatography electron impact mass spectrometry selected ion monitoring system. Ions at m/z 219 [MHCl2+2]+˙ from residual 1,2,3,4,5,6-hexachlorocyclohexane isomers and m/z 224 [M2HCl2+2]+˙ from dual laboratory-synthesized deuterated internal standards were monitored for the estimation. Linearities of individual 1,2,3,4,5,6-hexachlorocyclohexane isomers with gas chromatography electron impact mass spectrometry selected ion monitoring were much wider than those with gas chromatography electron capture detection, and it could be said that dilution or concentration of the sample extract was commonly unnecessary. In addition, carrier effects of deuterated internal standards with representative water samples and selectivity of the method in comparison with gas chromatography electron capture detection were clearly shown. In field experiments, total 1,2,3,4,5,6-hexachlorocyclohexane levels were from 166.54 to 7.40 parts per trillion (ng L−1).

Further specific extracellular phenolic glycolipid antigens and a related diacylphthiocerol from Mycobacterium leprae.

Mycobacterium leprae in infected armadillo tissue produces extracellular phthiocerol-containing lipids in amounts well in excess of the bacterial mass. The principal component (1.38 mg in 1 g of liver, wet weight, containing 3.7 X 10(10) M. leprae bacilli) consists of a mixture of two phthiocerol homologs, 3-methoxyl-4-methyl-9, 11-dihydroxyoctacosane and 3-methoxyl-4-methyl-9, 11-dihydroxytriacontane, (formula: see text); in which the hydroxyl functions are acylated by a mixture of three 'mycocerosic acids': 2,4,6,8-tetramethylhexacosanoate, 2,4,6,8-tetramethyloctacosanoate, and 2,4,6,8-tetramethyltriacontanoate. The structures were established by saponification of the native lipid, direct probe electron impact- or chemical ionization-mass spectrometry of the phthiocerol or its permethylated derivative, and gas-liquid chromatography-electron impact-mass spectrometry of the methyl esters of the fatty acids. In addition to the previously reported M. leprae-specific triglycosylphenolicdiacyl phthiocerol (Hunter, S. W., Fujiwara, T., and Brennan, P. J. (1982) J. Biol. Chem. 257, 15072-15078), the extracellular products contain small amounts (about 60 micrograms/g of infected liver, wet weight) of two other phenolic glycolipids, one of which (Phenolic Glycolipid III) has been structurally elucidated, (formula: see text); assuming certain enantiomeric configurations for the sugar substituents; the R-acyl functions are identical with those in the diacylphthiocerol. Phenolic Glycolipid-III reacts in enzyme-linked immunosorbent assays with sera from patients with leprosy and with rabbit antisera raised against whole M. leprae. The phthiocerol-containing lipids may be synonymous with the electron transparent capsules of M. leprae, and their unreactive state may confer on them the role of passive protectors of the bacillus.

Measurement of bile acid kinetics in human serum using stable isotope labeled chenodeoxycholic acid and capillary gas chromatography electron impact mass spectrometry.

A non invasive method for measurement of bile acid kinetics in serum using (24-13C)chenodeoxycholic acid has been developed. After oral administration of 50 mg (24-13C)chenodeoxycholic acid, the exponential decay of the 13C atom percent excess was measured in serum using capillary gas chromatography mass spectrometry. This required that isotope ratios were measured with high accuracy and coefficients of variation less than 1% by means of selected ion monitoring and scan averaging. The clinical applicability was tested by repeated determination of pool size, fractional turnover and synthesis rate of chenodeoxycholic acid in one healthy volunteer. This method permitted the determination of pool size, synthesis and conversion of chenodeoxycholic acid into lithocholic acid in man without the use of radioactive tracers and without repeated duodenal intubation.

Organometallic geochemistry. Isolation and identification of organoarsenic compounds from Green River Formation oil shale

A Green River Formation oil shale sample was crushed and extracted with refluxing methanol and analysed by high performance liquid chromatography in combination with graphite furnace atomic absorption detection (h.p.l.c.–g.f.a.a.) to provide evidence for the presence of methyl- and phenyl-arsonic acids and the arsenate ion; further evidence for the acids' identification was provided by derivatization with 3-methylcatechol to form the corresponding five-co-ordinate organoarsenic catecholates followed by capillary column gas chromatography–electron impact mass spectrometry (g.c.–e.i. m.s.) analysis.

Nitrated polycyclic aromatic hydrocarbons in urban air particles

The organic extract of urban air particles from St. Louis, MO, was fractionated by high-performance liquid chromatography. The moderately polar fraction was characterized by gas chromatography-electron impact and methane negative ion chemical ionization mass spectrometry. The compounds identified in the sample included nitronaphthalene, 9-nitroanthracene, 3-nitrofluoranthene, 1-nitropyrene, arenecarbonitriles, and several polycyclic ketones, quinones, and anhydrides. These studies represent the first mass spectrometric evidence of nitroaromatics in urban air particles.

Analysis of synthetic mixtures of partially methylated alditol acetates by capillary gas chromatography, gas chromatography-electron impact mass spectrometry and gas chromatography-chemical ionization mass spectrometry

The identification of naturally methylated neutral monosaccharides in acid hydrolysates as their alditol acetates requires appropriate standards. The availability of such standards also facilitates the analysis of complex mixtures of partially methylated alditol acetates (PMAAs) which appear upon methylation analysis of polysaccharides. For this purpose the alditols of eight common monosaccharides have been partially methylated using the Haworth methylation. The resulting mixtures of partially methylated alditols have been acetylated and analysed by capillary gas chromatography, gas chromatography—electron impact mass spectrometry and gas chromatography—chemical ionization mass spectrometry. Identification of the obtained PMAAs is further elaborated by reduction of the aldoses with sodium borodeuteride and the use of partially methylated aldoses or disaccharides.

Identification of double bond positions in dodecenyl acetates by electron impact mass spectrometry.

Seven positional isomers (Δ5M-Δ11) of dodecenyl acetate were analyzed, without any prior chemical modifications by combined gas-liquid chromatography-electron impact mass spectrometry. The position of the double bonds in the alkenes could be located by the relative intensities of the predominant fragment ions, depending upon whether or not the value of the ratio was over unity.

Metabolism of oxybutynin: Establishment of desethyloxybutynin and oxybutyninN-oxide formation in rat liver preparations using deuterium substitution and gas chromatographic mass spectrometric analysis

Oxybutynin is rapidly metabolized in rat liver microsomes. Two major primary oxidation products were identified as N-desethyl oxybutynin and oxybutynin N-oxide. Deuterium substituted substrate was used to aid the identification. N-Desethyl oxybutynin was characterized by gas chromatography electron impact mass spectrometry as its trifluoroacetamide derivative and oxybutynin N-oxide was indicated by the presence of a decomposition product, 2-oxo-3-butenyl-2 cyclohexyl-2-phenylglycolate, as elucidated from the gas chromatographic mas spectrometric analysis. The formation of this product from synthetic oxybutynin N-oxide was verified and occurs by two consecutive rearrangements upon thermolysis of the unstable N-oxide. Attempted titanous chloride reduction of oxybutynin N-oxide resulted in the formation of the hydrolytic products 2-cyclohexyl-2-phenylglycolic acid and 4-diethylamino-2-butynol.

Gas chromatography chemical ionization mass spectrometry of glucosinolate derivatives

Gas chromatography chemical ionization mass spectrometry has been found to possess advantages over gas chromatography electron impact mass spectrometry for the structural elucidation of glucosinolates (mustard oil glycosides), separated as the volatile per-trimethylsilyldesulpho derivates. The method has been applied to both mixtures of standard glucosinolates and also to extracts of plant tissue. The technique demonstrates the versatility of mass spectrometry in glucosinolate identification.

Determination of uracil and thymine and their nucleosides and nucleotides in picomole amounts by gas chromatography mass spectrometry selected ion monitoring.

A stable isotope dilution method is presented by which uracil (Ura) and thymine (Thy) can be determined with high precision and sensitivity at the picomole level utilizing stable isotope dilution and gas chromatography electron impact mass spectrometry in the selected ion monitoring mode. [15N2]Ura and [2H3]Thy served as internal standards. The molecular ions as well as the [M-CH3]+ ion fragments of silylated Ura and Thy (Ura-TMS and Thy-TMS) were suitable for the assay which provides evidence of specificity, if identical results are obtained at both ions. Nucleosides and nucleotides of Ura and Thy were determined following quantitative hydrolysis in 6 N HCl at 180 degrees C for two hours. Other hydrolysis procedures did not give satisfactory results. Levels of free Ura and Thy were measured in human and rat plasma after solvent extraction with a sensitivity of 20-40 pm ml-1 demonstrating ready applicability of the assay method to biological samples. The potential physiological role of circulating Ura and Thy is discussed.

Acetylated methylmannose polysaccharide of Streptomyces griseus. Locations of the acetyl groups.

The positions of esterification of the 4 to 5 acetyl residues in the acetylated methylmannose-containing polysaccharide from Streptomyces griseus have been established by the methyl replacement technique, wherein ester substituents are specifically replaced with methyl ether substituents. The newly incorporated methyl groups were distinguished from 3-O-methyl groups by the use of polysaccharide containing radioactively labeled endogenous methyl groups. The positions of methyl group localization were established by a proton magnetic resonance study of the intact methyl-replaced polysaccharide combined with an analysis of the constituent monosaccharides by gas-liquid chromatography-electron impact mass spectrometry of their alditol acetate derivatives. These studies demonstrate that the acetyl groups are located at position 6 of approximately half of the 10 contiguous alpha(1 leads to 4)-linked 3-O-methyl-D-mannose residues. Purification of the polysaccharide was accomplished by an added step involving affinity chromatography on a column containing immobilized palmitoyl residues. The affinity of the polysaccharide for this long chain lipid suggests that its plays a role similar to the methylmannose-containing polysaccharide of Mycobacterium smegmatis in its regulation of the bacterium's fatty acid synthetase.

The analysis of terbutaline in biological fluids by gas chromatography electron impace mass spectrometry.

A highly sensitive and specific assay is described for the bronchodilator drug terbutaline in human plasma and urine, based on single ion monitoring gas chromatography mass spectrometry and employing a homologue of the drug as internal standard. Recovery of terbutaline and internal standard into ethyl acetate is effected at pH 9.8, while back-extraction into dilute acid serves to purify the initial extract. Following preparation of O-TMS, N-TFA derivatives, the drug and its homologue are detected by selected ion monitoring of their common base ion at m/e 355. The limit of detection of terbutaline by this procedure is 0.3 ng ml-1 from a 4 ml sample of plasma.

Identification of amino sugars from bacterial lipopolysaccharides by gas chromatography electron impact and chemical ionization mass spectrometry.

Amino sugars isolated from lipopolysaccharides of Brucella suis, Brucella abortus and Neisseria gonorrhoeae colony types 1 and 4 were identified using gas chromatography electron impact and chemical ionization mass spectrometry. Lipopolysaccharides were obtained by aqueous ether or aqueous phenol extraction. Isolated lipopolysaccharides were hydrolyzed in 1% acetic acid followed by hydrolysis of the polysaccharide moiety in 2 NHCl for 6 h at 100 degrees C. Amino sugars were first isolated by elution from Dowex 50 H+ and then N-acetylated, followed by trimethylsilylation. Trimethylsilyl ethers of 2-acetamido-2-deoxysugars; N-acetylglucosamine, N-acetylmannosamine, N-acetylgalactosamine, and a 2-acetamido-2.6-dideoxysugar, N-acetylquinovosamine, were identified by their fragmentation patterns. In the electron impact mode, N-acetylglucosamine and N-acetyl-galactosamine were distinguished from one another by comparing peak intensities at m/e 233 and 305. However, N-acetylglucosamine and N-acetylmannosamine could not be differentiated by electron impact mass spectrometry. In the chemical ionization mode, N-acetylglucosamine and N-acetylmannosamine both with base peaks at m/e 494, could be distinguished from N-acetylgalactosamine and N-acetylquinovosamine by their base peaks at m/e 420 and 332, respectively. N-Acetylglucosamine and N-acetylmannosamine were differentiated from one another by comparing peak intensities at m/e 330, 404, 420, and 510 [MH]+. This is the first report of chemical ionization mass spectrometry applied to the identification of amino sugars in bacterial lipopolysaccharides and shows that some 2-amino-2-deoxysugars can be differentiated by both electron impact and chemical ionization mass spectrometry.

Squalene and other unsaturated hydrocarbons, inBryocladia cuspidata

By gas chromatography-electron impact mass spectrometry the red algaBryocladia cuspidata, was found to contain n-pentadecane and n-heptadecane. Gas chromatography-chemical ionization mass spectrometry indicated the presence of squalene as well as a C21 pentaene and a C21 hexaene, tentatively identified as 1,6,9,12,15-heneicosapentaene and 1,6,9,12,15,18-heneicosahexaene.

Use of new silylating agents for identification of hydroxylated steroids by gas chromatography and gas chromatography mass spectrometry.

Differences in methylene unit values were used for the determination of the hydroxyl group number of a steroid by means of gas chromatography. This index is defined as the difference in the methylene unit value between trimethylsilyl and other dimethylalkylsilyl (DMAS) ether derivatives of hydroxylated steroids, namely dimethylethylsilyl (DMES) and dimethyl-n-propylsilyl (DMPS) ethers. The reactivities of DMES and DMPS imidazoles as silylating agents were nearly equal to that of TMS-I. Mass spectra of these derivatives were characterized by the molecular ion cluster, [M]+., [M-15]+ and [M-29]+ (or [M-43]+). The molecular ion cluster of these derivatives is most useful for estimating the molecular weight. Therefore, these DMAS ethers provide valuable information for structural elucidation of hydroxylated steroids by gas chromatography electron impact mass spectrometry.

Identification of glucosyl sphingosine from Gaucher's spleen by gas chromatography-electron impact and GC-chemical ionization mass spectrometry.

Glucosyl sphingosine was isolated from the spleen of a patient with adult-type Gaucher's disease. The yield of purified glucosyl sphingosine was 9.3 nmoles/g wet tissue. The gas chromatography-chemical ionization mass spectrum of acetylated glucosyl sphingosine showed peaks due to the presence of ions formed by successive loss of acetic acid (mass 60) from the molecular ion (QM+, 714). Fragments from acetylated sugar, m/e 331, and from the sphingosine residue, m/e 306, were also detected. The GC-CI mass spectrum of the trimethylsilyl derivative of glucosyl sphingosine showed peaks due to the molecular ion (QM+, 822), ions from the sugar moiety (m/e 361, 271), and ions from the sphingosine base (m/e 264, 280). Fragmentation analysis of the purified sample by GC-EI and GC-CI mass spectrometry confirmed the structure glucopyranosyl(1 leads to 1)-1,3-dihydroxy-2-amino-4-octadecene.

Letter: Use of new silylating agents for identification of hydroxylated steroids by gas chromatography-electron impact-mass spectrometry.

A difference of methylene unit value, Δ [MU], was used for the determination of hydroxyl group number of steroid by means of gas chromatography. This index is defined by the difference in the methylene unit value between trimethylsilyl and other dimethylalkylsilyl (DMAS) ether derivatives, namely dimethylethylsilyl (DMES) and dimethyl-n-propylsilyl (DMPS) ethers, of hydroxy-steroid. Mass spectra of these derivatives were characterized by the molecular ion cluster, M, M-15 and M-29 (or M-43), where the fragment ion of M-29 (or M-43) appeared in the most case as a base peak. The molecular ion cluster of these derivatives is of great use for estimating the molecular weight. There-fore, these DMAS ethers provide a valuable information for structural elucidation of hydroxy-steroids by gas chromatography-electron impact-mass spectrometry.