Gas chromatographic method for the simultaneous determination of S-p-toluylmercapturic acid and S-phenylmercapturic acid in human urine

An analytical method for the simultaneous determination of S-p- toluylmercapturic acid (p-TMA) and S-phenylmercapturic acid (PMA) in human urine is described. PMA is a common biomarker for benzene exposure, whereas p-TMA is detected for the first time in the urine of workers occupationally exposed to toluene. Before analysis, the acidified urine samples were spiked with S-(p-fluorine)phenylmercapturic acid as internal standard. After extraction with ethyl acetate and derivatization with diazomethane, the methylethers were detected by gas chromatography coupled with mass selective detection. The criteria of reliability were satisfactory. The imprecisions within the series and from day to day were in a range from 4.9 to 13.4%, and the detection limits were 1 μg/L for PMA and 5 μg/L for p-TMA. The application of the method to urine samples of 32 subjects exposed to a median external concentration of 63 ppm toluene resulted in a median p-TMA excretion of 20 μg/L. However, no p-TMA was detected in the urine of subjects without occupational exposure to toluene. The determination of arylmercapturic acids is also suitable for biological monitoring of mixed exposures to toluene and benzene.