Determination of Seven Urinary Metabolites of Organophosphate Esters using Liquid Chromatography-Tandem Mass Spectrometry

Abstract

Abstract A simple method was developed for simultaneous determination of seven urinary metabolites of organophosphate esters (OPs) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Based on different physical and chemical properties of these OP metabolites, their enrichment and clean-up were performed through solid phase extraction to obtain high-efficient solid phase extraction cartridges, and the washing and elution conditions were optimized. At the same time, the kinetic parameters and mass spectrometry parameters were investigated for getting the qualitative and quantitative characteristic ion pairs for analysis of each metabolites. The results showed that the Oasis WAX solid phase extraction cartridge was suitable for sample enrichment and clean-up, and the optimal elution solvents were 2 mL of 5% ammonia in methanol and 2 mL of methanol. The recoveries of six analytes ranged from 60.5 to 104.0%, whereas the recovery of diethyl phosphate ranged from 17.8% to 36.2%. The complete baseline separations of seven analytes were achieved under optimized chromatographic conditions. The limits of detection and limits of quantification of the seven analytes ranged from 0.005 to 0.2 μg L−1 and 0.02 to 0.5 μg L−1, respectively. The intra-day and inter-day precision results (RSD = 15.4%) showed that this method had good stability and reproducibility. This method was subsequently used to determine OP metabolites in 10 urine samples from the general population in Guangzhou city. The concentrations of the seven OP metabolites in urine samples ranged from 0.5 to 6.7 μg L−1.