Determination of n-hexane metabolites by liquid chromatography/mass spectrometry. 1. 2,5-hexanedione and other phase I metabolites in untreated and hydrolyzed urine samples by atmospheric pressure chemical ionization

Application of liquid chromatography–mass spectrometry to biomonitoring of exposure to industrial chemicals

Recent advances on biomarker research are discussed, primarily relying on experience gained with technologies based on liquid chromatography-tandem mass spectrometry (LC-MS-MS). Determination of urinary metabolites of industrial chemicals (n-hexane, benzene, toluene, and styrene) in samples from occupationally exposed workers and controls was performed by LC-MS-MS with either electrospray (ESI) or atmospheric pressure chemical ionization (APCI), as appropriate. Both phase I and II metabolites (glucuronides, sulfates, and mercapturic acids) can be detected with little or no sample manipulation, thus allowing the identification of a number of artifacts and "new" metabolites. However, experimental evidence indicates the need for properly addressing the matrix effect, which is always associated with the analysis of biological samples. Both efficient sample preparation and the use of isotopically labeled internal standards seem to be necessary to develop validated quantitative methods.

Free and total 2,5-hexanedione in biological monitoring of workers exposed to n-hexane in the shoe industry

OBJECTIVES

To analyse the role of total 2,5-hexanedione (2,5-HD) compared with free 2,5-HD as a biological indicator of exposure to n-hexane at work.

METHODS

One-hundred and thirty two workers in contact with this solvent during their occupation in the shoe industry in the province of Alicante (Spain) were studied. Environmental and biological tests were carried out analysing variations of the concentration of the metabolite in urine corresponding to different working conditions. Environmental exposure was evaluated in each work place using active personal monitors and measured by gas chromatography (GC). Dichloromethane extracts of the urine samples collected at the end of the working shifts were analysed, before (determining free 2,5-HD, the toxic metabolite) and after acid hydrolysis (pH 0.1) (yielding the total 2,5-HD) and also by GC. The concentration of conjugated metabolite 4,5-dihydroxy-2-hexanone was calculated from the difference between total and free 2,5-HD.

RESULTS

Free 2,5-HD represented an average of 14.2% of the total 2,5-HD determined in urine, and this percentage increased significantly (P<0.01) with higher environmental levels of acetone. Other factors, such as absorption through the skin (depending on the use of gloves) and the day on which samples were taken also significantly affected the relation between the two indicators and their respective relationships with environmental concentrations of n-hexane.

CONCLUSION

Although analyses of the relationship between the levels of atmospheric n-hexane and those of metabolites in urine show a greater correlation for total 2,5-HD than for free 2,5-HD, our results suggest that free 2,5-HD could be a better indicator in evaluating risk of exposure to n-hexane, since the concentration is directly related to the neurotoxic effect.

Liquid chromatography-mass spectrometry in the study of the metabolism of drugs and other xenobiotics

The application of liquid chromatography-mass spectrometry (LC/MS) to the study of metabolism of drugs and other xenobiotics is reviewed. Original research papers covering the period from 1998 to early 2000 and concerning the use of LC/MS in the study of xenobiotic metabolism in humans and other mammalian species are reviewed. LC/MS interfaces, sample preparation steps, column types, mobile phases and additives, and the type of metabolites detected are summarized and discussed in an attempt to identify the current and future trends in the use of LC/MS for metabolism studies. Applications are listed according to the parent xenobiotic type and include substances used in therapeutics, drug candidates, compounds being evaluated in clinical trials, environmental pollutants, adulterants and naturally occurring substances.