Determination of S-phenylmercapturic acid by GC-MS and ELISA: a comparison of the two methods

Abstract

S-phenylmercapturic acid (PMA) is a specific urinary biomarker of benzene at exposure levels lower than 1 ppm. However, measuring PMA in urine is an expensive task by either GC or HPLC due to the necessity of extensive sample pretreatment. In the present study, a commercial chemiluminescence enzyme-linked immunosorbent assay (ELISA) test for PMA and GC-MS were used for screening urine samples of 60 workers employed in petrochemical settings. The ELISA results were evaluated by comparison with the GC-MS. Overall, the ELISA test proved sensitive (limit of detection = 0.1 µg l⁻¹), rapid, robust and reliable, affording results in good agreement with the GC-MS (54% of measurements) and no false-negatives. On the other hand, 46% of the ELISA assays were assigned as false-positives (arbitrarily established when ELISA >5 µg l⁻¹, GC-MS <5 µg l⁻¹) and a correlation coefficient of 0.687 was calculated between the two methods. It appears that urinary PMA routine biomonitoring on large numbers of samples is carried out in a cost-effective and rapid approach by preliminary screening with the ELISA assay followed by GC-MS confirmation of concentrations exceeding the biological exposure index for PMA.

Keywords: :

• S-phenylmercapturic acid
• chemiluminescence
• enzyme-linked immunosorbent assay (ELISA)
• gas chromatography-mass spectrometry (GC-MS)
• benzene
• biomonitoring

Acknowledgements

The authors thank Dr Emanuele Attolino, University of Pisa, for kindly supplying the labelled internal standard [¹³C₆]-PMA.