Determination of the urinary benzene metabolites S-phenylmercapturic acid and trans,trans-muconic acid by liquid chromatography-tandem mass spectrometry

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Abstract
To investigate how various levels of exposure affect the metabolic activation pathways of benzene in humans and to examine the relationship between urinary metabolites and other biological markers, we have developed a sensitive and specific liquid chromatographic–tandem mass spectrometric assay for simultaneous quantitation of urinary S-phenylmercapturic acid (S-PMA) and trans,trans-muconic acid (t,t-MA). The assay involves spiking urine samples with [13C6]S-PMA and [13C6]t,t-MA as internal standards and clean up of samples by solid-phase extraction with subsequent analysis by liquid chromatography coupled with electrospray-tandem mass spectrometry-selected reaction monitoring (LC–ES–MS/MS–SRM) in the negative ionization mode. The efficacy of this assay was evaluated in human urine specimens from smokers and non-smokers as the benzene-exposed and non-exposed groups. The coefficient of variation of runs on different days (n = 8) for S-PMA was 7% for the sample containing 9.4 μg S-PMA/l urine, that for t,t-MA was 10% for samples containing 0.07 mg t,t-MA/l urine. The mean levels of urinary S-PMA and t,t-MA in smokers were 1.9-fold (P = 0.02) and 2.1-fold (P = 0.03) higher than those in non-smokers. The mean urinary concentration (±SE) was 9.1 ± 1.7 μg S-PMA/g creatinine [median 5.8 μg/g, ranging from not detectable (1 out of 28) to 33.4 μg/g] among smokers. In non-smokers' urine the mean concentration was 4.8 ± 1.1 μg S-PMA/g creatinine (median 3.6 μg/g, ranging from 1.0 to 19.6 μg/g). For t,t-MA in smokers' urine the mean (±SE) was 0.15 ± 0.03 mg/g creatinine (median 0.11 mg/g, ranging from 0.005 to 0.34 mg/g); the corresponding mean value for t,t-MA concentration in non-smokers' urine was 0.07 ± 0.02 mg/g creatinine [median 0.03 mg/g, ranging from undetectable (1 out of 18) to 0.48 mg/g]. There was a correlation between S-PMA and t,t-MA after logarithmic transformation (r = 0.41, P = 0.005, n = 46).