Ion-pair-based hollow-fiber liquid-phase microextraction combined with high-performance liquid chromatography for the simultaneous determination of urinary benzene, toluene, and styrene metabolites.

In the current study, a novel technique for extraction and determination of trans,trans-muconic acid, hippuric acid, and mandelic acid was developed by means of ion-pair-based hollow fiber liquid-phase microextraction in the three-phase mode. Important factors affecting the extraction efficiency of the method were investigated and optimized. These metabolites were extracted from 10 mL of the source phase into a supported liquid membrane containing 1-octanol and 10% w/v of Aliquat 336 as the ionic carrier followed by high-performance liquid chromatography analysis. The organic phase immobilized in the pores of a hollow fiber was back-extracted into 24 μL of a solution containing 3.0 mol/L sodium chloride placed inside the lumen of the fiber. A very high preconcentration of 212- to 440-fold, limit of detection of 0.1-7 μg/L, and relative recovery of 87-95% were obtained under the optimized conditions of this method. The relative standard deviation values for within-day and between-day precisions were calculated at 2.9-8.5 and 4.3-11.2%, respectively. The method was successfully applied to urine samples from volunteers at different work environments. The results demonstrated that the method can be used as a sensitive and effective technique for the determination of the metabolites in urine.