An electrospray ionization tandem mass spectrometry based system with an online dual-loop cleanup device for simultaneous quantitation of urinary benzene exposure biomarkers trans,trans-muconic acid and S-phenylmercapturic acid

An electrospray ionization tandem mass spectrometry (ESI‐MS/MS) system with an online dual‐loop cleanup device was developed for simultaneous quantitation of the urinary benzene exposure biomarkers trans,trans‐muconic acid (ttMA) and S‐phenylmercapturic acid (SPMA). The cleanup device was constructed from an autosampler, two electrically operated two‐position switching valves, a reversed‐phase C18 trap cartridge, a 200‐μL loop, and two solvent‐delivery pumps. The device was interfaced directly with a triple‐quadrupole mass spectrometer and fully controlled by computer software and hardware. Because isotope dilution by introducing 13C‐labeled ttMA and SPMA as internal standards was employed, the precision of the analytical system was high (for ttMA, intra‐ and inter‐day CV values ranged from 3.82–4.53%; for SPMA, 2.13–7.06%). The calibration curves obtained using human urine spiked with ttMA were linear from 15.6–4000 μg/L (R = 0.9998) and SPMA at concentrations from 0.78–200 μg/L (R = 0.9993). The method detection limit (MDL) for SPMA was 0.23 μg/L. The MDL of ttMA could not be determined accurately because of unavailability of an appropriate blank urine matrix, but was estimated to be lower than 7.43 μg/L. Without tedious manual sample cleanup procedures the analytical system is fully automated and is therefore useful for high‐throughput simultaneous determination of urinary ttMA and SPMA. The sample throughput is roughly 100 samples per day. With the selectivity and the sensitivity provided by MS/MS detection, the analytical system can be used for large‐scale monitoring of environmental or occupational exposure of humans to benzene. Copyright © 2004 John Wiley & Sons, Ltd.