Development and validation of an LC-MS/MS method with precolumn derivatization for the determination of dimethoxyethyl phthalate metabolites ethylene glycol methyl ether and methoxyacetic acid in rat plasma.

Dimethoxyethyl phthalate (DMEP) is an industrial phthalates reagent exposed to human body. Its hydrolytic metabolite ethylene glycol methyl ether (EGME) and further oxidative metabolite methoxyacetic acid (MAA) have reproductive and developmental toxicity, and the latter is more toxic than the former. However, due to the lack of sensitive and reliable analytical method, the in vivo clearance and biotransformation of EGME and MAA is poorly understood. In order to evaluate their toxicokinetic profiles, a precolumn derivatization liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous determination of EGME and MAA in rat plasma. After a simple protein precipitation procedure, the sample was derivatized with p-toluene sulfonyl isocyanate (PTSI) and 4-bromo-N-methylbenzylamine (4-BNMA), separated by gradient elution on HSS T3 column, and detected by electrospray ionization (ESI) source in positive multiple reaction monitoring (MRM) mode. The results of the method validation showed that EGME had good linearity in the range of 2.00-400 ng/mL and MAA in the range of 5.00-1000 ng/mL. The intra- and inter-day accuracy and precision were within acceptable limits ( ± 15 %) at all concentrations. This validated method was successfully applied to characterize the toxicokinetics of EGME and MAA in rats following a gavage administration of 50 mg/kg DMEP.