Extraction of the toluene exposure biomarkers hippuric acid and methylhippuric acid using a magnetic molecularly imprinted polymer, and their quantitation by LC-MS/MS

A magnetic polymer was molecularly imprinted with hippuric acid (HA) to obtain a nanomaterial with an architecture of type Fe3O4@SiO2@MIP. It was used as a sorbent for magnetic solid phase extraction of HA and methylhippuric acids (2-MHA, 3-MHA, 4-MHA) from urine samples. The respective imprinting factor are 4.6, 2.7, 2.0 and 1.8, respectively, and the selectivity coefficients are 1.7, 2.3 and 2.6. The effects of adsorbent amount, extraction time, pH value, ionic strength, desorption solvent and desorption time on the extraction of HA and MHA were investigated. Following elution with 1mM NaOH solution, the 4 HAs were quantified by ultra-performance liquid chromatography with mass spectrometric detection. Under the optimal experimental conditions, the limits of detection (at S/N=3) range between 89ngL(-1) (for HA) and 170ngL(-1) (for 4-MHA), the limits of quantification (at S/N=10) range between 300ngL(-1) (for HA) and 570ngL(-1) (for 4-MHA), the linear range extends from 500ngL(-1) to 10mgL(-1), the relative standard deviations of intra-day range between 6.4 and 9.6% (for n=6 at 10gL(-1)) and inter-day range between 9.2 and 11.5% (for n=6 at 10gL(-1)). The method was successfully applied to the analysis of HA and MHA in (spiked) urine, and good recoveries were obtained.