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At least 469 records · Page 26Linked to original sources
PubMed1994

Analysis of amino acids by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry: simultaneous derivatization of functional groups by an aqueous-phase chloroformate-mediated reaction.

The one-step ethyl chloroformate derivatization of amino acids in an aqueous medium is extended with the use of a variety of alkyl chloroformate reagents. This provides a new and convenient procedure for preparing esters with different alkoxy groups. A new mechanism for esterification during chloroformate derivatization is proposed based on the formation of an intermediate mixed carboxylic-carbonic acid anhydride followed by the exchange with an alcohol. Among the different reagents investigated, isobutyl chloroformate derivatized amino acids were found to provide more sensitivity for analyses by GC-flame ionization detection and GC-MS relative to derivatives prepared by other alkyl chloroformates.

Amino Acids↗
PubMed1994

Application of gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry to the analysis of chemical warfare samples, found to contain residues of the nerve agent sarin, sulphur mustard and their degradation products.

Samples of clothing, grave debris, soil and munition fragments, collected from the Kurdish village of Birjinni, were analysed by GC-MS with selected ion monitoring (SIM) for traces of chemical warfare agents and their degradation products. Positive analyses were confirmed, where possible, by full scan mass spectra, or at low concentrations by additional GC-MS-SIM analysis using chemical ionisation, by higher resolution GC-MS-SIM, and by GC-tandem mass spectrometry using multiple reaction monitoring. Sulphur mustard and/or thiodiglycol were detected in six soil samples; isopropyl methylphosphonic acid and methylphosphonic acid, the hydrolysis products of the nerve agent sarin, were detected in six different soil samples. Trace amounts of intact sarin were detected on a painted metal fragment associated with one of these soil samples. The results demonstrate the application of different GC-MS and GC-MS-MS techniques to the unequivocal identification of chemical warfare agent residues in the environment at concentrations ranging from low ppb to ppm (w/w). They also provide the first documented unequivocal identification of nerve agent residues in environmental samples collected after a chemical attack.

Chemical Warfare Agents↗
PubMed1985

Determination of polysaccharide linkage and branching by reductive depolymerization. Gas-liquid chromatography and gas-liquid chromatography-mass spectrometry reference data.

A series of partially methylated anhydro-D-alditol acetates has been prepared and analyzed by g.l.c. and g.l.c.-m.s. The reference compounds were obtained by reductive cleavage of permethylated and partially methylated standard methyl glycosides, and standard di-, tri-, and tetra-saccharides of known composition and linkage. Structural characterization included retention times on g.l.c. using DB-225 capillary columns and mass spectrometry in both the chemical- and electronionization modes. This compiled library allows further evaluation of the applicability of the reductive cleavage procedure for determining linkage or branching (or both) of new and more complex oligosaccharides. The technique has been applied to microgram amounts of a bacterial-membrane oligosaccharide and to a saccharide obtained from the urine of a mannosidosis patient. The procedures are simple, reliable, and applicable to small amounts of isolated biological materials.

Acetylation↗
PubMed1984

Gas chromatographic and gas chromatographic-mass spectrometric analysis of organic acids in plasma of patients with chronic renal failure.

Apart from increased concentrations of aliphatic dicarboxylic acids and phenolic aromatic acids in plasma from patients with chronic renal failure, there is large elevation of a furanoid acid, 3-carboxy-4-methyl-5-propyl-2- furanpropionic acid, and of hippuric acid. The levels of 3-hydroxy- and 4- hydroxyhippuric acid are also raised. The quantitative results are as follows: furanoid acid in hemodialysis patients, 1.4 +/- 0.6 mg/dl; in healthy individuals, 0.2 +/- 0.1 mg/dl; hippuric acid in hemodialysis patients, 9.8 +/- 6.5 mg/dl; in health individuals, 0.4 +/- 0.5 mg/dl. Both compounds are dialysable, but less effectively than creatinine and urea. The mean elimination rate of the furanoid acid is only 21%.

Adolescent↗
PubMed2002

Analysis of free and bound volatiles by gas chromatography and gas chromatography-mass spectrometry in uncased and cased tobaccos.

The free and bound volatiles of tobaccos were analyzed by capillary GC and GC-MS. Bound volatiles were isolated by dichloromethane extraction followed by stream distillation continuous extraction (SDE) at pH 2.5 acid hydrolysis. The bound aromatic compounds were hydrolyzed by acid at pH 2.5, and the bound volatiles were liberated and extracted into dichloromethane by SDE simultaneously. In total, 23 volatiles were identified, with neophytadiene, 2-ethyl hexanol, damascenone, benzene ethanol, palmitic acid, stearic acid, linoleic acid, farnesyl acetone, 3-oxo-ionol, and megastigmatrienone being the major components. They consisted mainly of compounds exhibiting aromatic characteristics. The quality and quantity of free and bound volatiles exhibited different distributions in uncased or cased tobaccos. The volatiles existed in higher amounts in bound form than in free form. Compared with uncased tobaccos, free form volatiles showed a decrease after the casing process, while bound volatiles showed an increase.

Chromatography, Gas↗
PubMed2002

Aroma compound analysis of Piper nigrum and Piper guineense essential oils from Cameroon using solid-phase microextraction-gas chromatography, solid-phase microextraction-gas chromatography-mass spectrometry and olfactometry.

The investigation of aroma compounds of the essential oils of dried fruits of black pepper (Piper nigrum) and black and white "Ashanti pepper" (Piper guineense) from Cameroon by means of solid-phase microextraction (SPME) was carried out for the first time to identify the odorous target components responsible for the characteristic odor of these valuable spices and food flavoring products. By means of GC-flame ionization detection (FID) and GC-MS (using different polar columns) the main compounds (concentration >3.0%, calculated as area of GC-FID analysis using a non-polar fused-silica open tubular RSL-200 column) of the SPME headspace samples of P. nigrum (black) and P. guineense (black and white) were found to be: P. nigrum (black)--germacrene D (11.01%), limonene (10.26%), beta-pinene (10.02%), alpha-phellandrene (8.56%), beta-caryophyllene (7.29%), alpha-pinene (6.40%) and cis-beta-ocimene (3.19%); P. guineense (black)--beta-caryophyllene (57.59%), beta-elemene (5.10%), bicyclogermacrene (5.05%) and alpha-humulene (4.86%); and P. guineense (white)--beta-caryophyllene (51.75%), cis-beta-ocimene (6.61%), limonene (5.88%), beta-pinene (4.56%), linalool (3.97%) and alpha-humulene (3.29%). The most intense odor impressions of the essential oils of the various dried pepper fruits were given byprofessional perfumers as follows: P nigrum (black)--fine, pleasant black pepper note; P. guineense (black)--black pepper top-note; and P. guineense (white)--pleasant white pepper note. These analytical results for the SPME headspace samples of three different pepper species from Cameroon are in accordance with the olfactoric data of the corresponding essential oils. A GC-sniffing technique was used to correlate the single odor impression of the identified SPME headspace volatiles of the three investigated pepper samples with the following results: themain compounds such as beta-caryophyllene, germacrene D, limonene, beta-pinene, alpha-phellandrene and alpha-humulene, as well as minor constituents such as delta-carene, beta-phellandrene, isoborneol, alpha-guaiene, sarisan, elemicin, calamenene, caryophyllene alcohol, isoelemicin, T-muurolol, cubenol and bulnesol, are of greatest importance for the characteristic pepper odor notes of these three Piper samples. Further aroma impressions can be attributed to mono- and sesquiterpenes, hexane, octane and nonane derivatives.

Chromatography, Gas↗
PubMed2003

Patterns in the precision of quantitative data from multicomponent gas chromatographic or gas chromatographic-mass spectrometric analysis.

The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed.

Chromatography, Gas↗