Gas chromatographic determination of benzene, toluene, ethylbenzene and xylenes using flame ionization detector in water samples with direct aqueous injection up to 250 microl.

A simple method of solventless extraction of volatile organic compounds (benzene, toluene, ethylbenzene and xylenes) from aqueous samples was developed. This method allows direct injection of large volume of water sample into a gas chromatograph using the sorption capacity of the sorbent Chromosorb P NAW applied directly in the injection port of gas chromatograph. The system prevent water penetration into a column, keep it adsorbed on its surface until the analytes are stripped into a column, and the residual water is purging using split flow. The limit of detection ranging from 0.6 for benzene to 1.1 microg l(-1) for o-xylene and limit of quantification ranging 2.0-3.6 microg l(-1) are lower that those reached by gas chromatography with flame ionization detection and direct aqueous injection before.

Analysis of hopanoids in bacteria involved in food technology and food contamination.

Hopanoids are pentacyclic triterpenoids which are believed to act as reinforcers of membranes in certain prokaryotic microorganisms. A rapid and sensitive method for their screening in bacteria was elaborated, involving extraction of nonsaponifiable lipids and the analysis by gas chromatography-mass spectrometry, selectively monitoring the ion of m/z = 191. Using the method, hopanoids were detected in strains of Acetobacter pasteurianus, but were found to be absent in lactic acid bacteria (Lactobacillus spp., Lactococcus spp.) and in food-contaminating bacteria (Salmonella spp., Listeria spp., Yersinia spp. and others).

Inhibition of ergosterol biosynthesis is not accompanied by a change in fatty acid composition in Saccharomyces cerevisiae treated with the antifungal agent 6-amino-2-n-pentylthiobenzothiazole.

The antifungal agent 6-amino-2-n-pentylthiobenzothiazole at a concentration of 40 microM lowered the specific growth rate of exponentially growing cultures of Saccharomyces cerevisiae by 36%. Treatment with 6-amino-2-n-pentylthiobenzothiazole inhibited the biosynthesis of ergosterol and caused an accumulation of the methylated sterol precursors ergosta-5,7-dienol and squalene, but had no significant effect on the composition and the rate of biosynthesis of fatty acids. The results indicate that neither the inhibition of ergosterol biosynthesis, nor the slowing-down of culture growth by this antifungal agent, led to a compensatory alteration in the pattern of fatty-acyl chains in membrane lipids. This finding contradicts the accepted wisdom for the action of a number of antifungal agents.

Gas chromatography-mass spectrometry-Fourier transform infrared spectrometry and high-performance liquid chromatographic characterization of mononitro- and dinitro-isomers from the nitration of N,N-dimethyldiphenylacetamide.

Gas chromatographic retention data, Fourier transform infrared and mass spectrometric (electron impact, electron attachment and methane chemical ionization) profiles are reported for the products of mono- and dinitration of N,N-dimethyldiphenylacetamide. Differentiations of analytical importance among isomers could be gathered by the study which led to their complete identification.

Interlaboratory study of identification and quantitation of multiresidue pyrethroids in agricultural products by gas chromatography-mass spectrometry.

This paper deals with the different GC-MS analytical conditions adopted by four laboratories in an attempt to confirm the accuracy of the GC-electron-capture detection (ECD) analytical results during the international collaborative study for the establishment of the AOAC Official Method 998. 01. What is especially noted is that two laboratories have conducted comparative analysis of the respective 12 blind samples with both methods of GC-ECD and GC-MS, and the analytical results of the two methods turn out to be basically identical. This fully demonstrates that GC-MS is not only an effective confirmation tool in the analysis of the pyrethroid residues but also of sufficient sensitivity regarding the maximum residue limit of determination prescribed by FAO/WHO. Moreover, its selectivity is better than GC-ECD.

Ultrasound effects on photochemical reactions, part 1: photochemical reactions of ketones with alkenes.

Ultrasound considerably enhances and simplifies photochemical reaction of cyclohexanone with cyclohexene. The Paterno-Büchi reaction of acetone with ethyl vinyl ether is enhanced by ultrasound and yields a different ratio of cis/trans oxetanes under sonication by comparison with the silent reaction. Sonication appears to affect the first reaction by homogenization of excited intermediates and by quenching the excited triplet state at the second reaction.

Classification and pattern recognition of acyclic octenes based on mass spectra.

Two SIMCA models were developed for the classification of acyclic octene isomers, which only form a fraction of a very complex product mixture obtained, for example, from the transformation of 1-butene. The effects of spectral transformation, namely autocorrelation and logarithmic intensity ratios transforms, and (square-root) scaling of the octane isomers mass-spectral data were investigated. Both the spectral-features preprocessing methods and scaling were found to be vital for an adequate development and improvement of the classification models. The best SIMCA models were successfully applied on gas-chromatography-mass spectroscopy (GC-MS) analysis collected from the dimerization of 1-butene over heterogeneous catalysts in the liquid phase.

Ergosterol depletion and 4-methyl sterols accumulation in the yeast Saccharomyces cerevisiae treated with an antifungal, 6-amino-2-n-pentylthiobenzothiazole.

In Saccharomyces cerevisiae treated with an antifungal agent, 6-amino-2-n-pentylthiobenzothiazole, levels of ergosterol and other 4-desmethylsterols were found to be significantly reduced. Major sterols in treated yeast were lanosterol, 4,4-dimethylzymosterol, 4-methylzymosterol and 4-methylfecosterol. A hypothesis is stated that the antifungal agent inhibits sterol demethylation at C-4 and forces the biosynthesis to a blind pathway ending by 4-methylfecosterol.