Analysis of urinary biomarkers for exposure to alkyl benzenes by isotope dilution gas chromatography-mass spectrometry

Ethyl chloroformate mediated gas chromatographic-mass spectrometric biomonitoring of acidic biomarkers of occupational exposure and endogenous metabolites in human urine

Numerous industrial organic pollutants such as aromates, alkoxyalcohols, other organic solvents and monomers are absorbed, metabolized, and finally excreted in urine mostly as carboxylic acids that are determined as biomarkers of exposure. For a number of these xenometabolites, biological limits (levels of biomarkers in biological material) have been established to prevent damage to human health. Till now, most of the analytical procedures used have been optimized for one or a few analytes. Here, we report a more comprehensive approach enabling rapid GC-MS screening of sixteen acidic biomarkers in urine that are metabolized in the human body from several important industrial chemicals; benzene, toluene, styrene, xylenes, alkoxyalcohols, carbon disulfide, furfural and N,N-dimethylformamide. The new method involves immediate in situ derivatization - liquid liquid microextraction of urine by an ethyl chloroformate-ethanol-chloroform-pyridine medium and GC-MS analysis of the derivatized analytes in the lower organic phase. The xenometabolite set represents diverse chemical structures and some of hippuric and mercapturic acids also provided unusual derivatives that were unambiguously elucidated by means of new ethyl chloroformates labeled with stable isotopes and by synthesis of the missing reference standards. In the next step, an automated routine was developed for GC-MS/MS analysis using a MetaboAuto® sample preparation workstation and the new method was validated for fourteen metabolites over the relevant concentration range of each analyte in the spiked pooled human urine. It shows good linearity (R² ≥ 0.982), accuracy (from 85% to 120%), precision (from 0.7% to 20%) and recovery (from 89% to 120%). The method performance was further successfully proved by GC-MS/MS analysis of the certified IP45 and RM6009 reference urines. Moreover, we show that the new method opens up the possibility for biomonitoring of combined and cumulative occupational exposures as well as for urinary metabolite profiling of persons exposed to harmful industrial chemicals.

Direct methyl esterification with 2,2-dimethoxypropane for the simultaneous determination of urinary metabolites of toluene, xylene, styrene, and ethylbenzene by gas chromatography-mass spectrometry

Objectives

The purpose of this study was to develop a simple and accurate gas chromatography‐mass spectrometry (GC‐MS) method for simultaneous determination of four urinary metabolites from four organic solvents, that is, hippuric acid (HA) from toluene, methylhippuric acid (MHA) from xylene, and mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene or ethylbenzene for biological monitoring.

Methods

The four metabolites were directly methyl‐esterified with 2,2‐dimethoxypropane and analyzed using GC‐MS. The proposed method was validated according to the US Food and Drug Administration guidance. The accuracy of the proposed method was confirmed by analyzing a ClinChek^®—Control for occupational medicine (RECIPE Chemicals +Instruments GmbH).

Results

Calibration curves showed linearity in the concentration range of 10‐1000 mg/L for each metabolite, with correlation coefficients >0.999. For each metabolite, the limits of detection and quantification were 3 mg/L and 10 mg/L, respectively. The recovery was 93%‐117%, intraday accuracy, expressed as the deviation from the nominal value, was 92.7%‐103.0%, and intraday precision, expressed as the relative standard deviation (RSD), was 1.3%‐4.7%. Interday accuracy and precision were 93.4%‐104.0% and 1.2%‐9.5%, respectively. The analytical values of ClinChek obtained using the proposed method were sufficiently accurate.

Conclusions

The proposed method is a simple and accurate which is suitable for routine analyses that could be used for biological monitoring of occupational exposure to four organic solvents.

The development of an analytical method for urinary metabolites of the riot control agent 2-chlorobenzylidene malononitrile (CS)

The analysis of biomedical samples such as urine and blood can provide evidence of exposure to chemicals for a range of applications including occupational exposure monitoring, detection of drugs of abuse, performance enhancement in sport and investigations of poisoning and incapacitation. This paper reports the development of an analytical method for two suspected urinary metabolites of the riot control agent 2-chlorobenzylidene malononitrile (CS): 2-chlorohippuric acid and 2-chlorobenzyl-N-acetylcysteine. 2-Chlorohippuric acid was identified in all 2h post-exposure samples from a set of urine samples taken from army recruits exposed to low levels of thermally dispersed CS during training. 2-Chlorobenzyl-N-acetylcysteine, a metabolite known to be formed in the rat, was not identified in any of the samples. The lower limit of detection (LLOD) for 2-chlorohippuric acid and 2-chlorobenzyl-N-acetylcysteine was 1ng/ml and 0.5ng/ml in pooled urine from the pre-exposed subjects. 2-Chlorohippuric acid was rapidly excreted but was detectable in the urine of 17 of the 19 subjects tested 20h after exposure.