Effect of hippuric acid on the gaschromatographic retention of S-phenylmercapturic acid.
S-phenylmercapturic acid (PMA) is one specific urinary biomarker of low-level benzene exposure. It is used for biological monitoring of benzene-exposed workers in the petrochemical industry and normally ranges from non-measurable to 10 microg/l levels in non-exposed non-smoking subjects. Benzene-exposure caused by workplace or lifestyle sources is frequently accompanied by toluene exposure, which can cause the occurrence of high levels (from 10 mg/l to more than 2000 mg/l) of hippuric acid (HA) in urine. Both solvents are toxic, and benzene is classified as a human carcinogen. The biological monitoring of benzene and toluene is therefore required for preventive care of exposed workers health. In this study a GC-MS method was adopted for measuring urinary PMA, which involved liquid-liquid extraction (LLE) with ethyl acetate from acidified urine and esterification with 0.5 N hydrochloric acid in methanol. The method evidenced a GC effect in a conventional HP-5 (30 m x 0.25 mm i.d., 0.25 microm film-thickness) methyl-phenylsilicone capillary column produced by HA on PMA. The results demonstrate that HA at concentrations as low as 250 mg/l can delay the elution of PMA and labelled internal standard from the column. The recognition and discussion of this particular GC phase soaking effect may be of help for those who are occupied in the determination of PMA and of urinary acidic metabolites by GC.