Selective determination of mandelic acid in urine using molecularly imprinted polymer in microextraction by packed sorbent

Mandelic acid (MA) is a major metabolite of ethylbenzene and styrene. For the first time, a selective, fast, and easy-to-use procedure was developed for the determination of MA in urine samples. The new procedure is based on MIMEPS, the combination of a molecularly imprinted polymer (MIP) and microextraction by packed sorbent (MEPS). High-performance liquid chromatography with ultraviolet detection (HPLC–UV) was used for the separation and determination of MA. The bulk polymerization method was used to synthesize the MIP, and the MIP and non-imprinted polymer (NIP) were characterized by Fourier transform infrared spectroscopy. The selectivity of the MIP was investigated in the presence of interferents. In addition, we investigated the various parameters that affect the performance of the MEPS, including the pH of the sample, the number of extraction cycles, sample volume, and the types and volumes of the washing and elution solvents. A six-point calibration curve was obtained in the range of 0.2–20 µg/mL (R2 = 0.9994). The extraction recovery was more than 88.8%. The limit of detection and the limit of quantitation were 0.06 and 0.2 µg/mL, respectively. The intra- and inter-day precisions were in the range of 3.6–4.7% and 3.8–5.1%, respectively. The accuracy was −8.4 to −11.1%. The optimized procedure was selective, sensitive, and rapid, and it was both user friendly and environmentally friendly. The sample preparation process took only about 5 min, so the MIMEPS–HPLC–UV procedure is recommended as an alternative for the biomonitoring of workers exposed to ethylbenzene and/or styrene.