Development of an ion-pair liquid chromatography–high resolution mass spectrometry method for determination of organophosphate pesticide metabolites in large-scale biomonitoring studies

•Proper method for the determination of 6 dialkyl phosphates in large-scale studies.•TPAF as ion-pair improves the MS sensitivity with respect to TBAA.•The robustness of the novel method was evaluated during 6 months.•The method allows the analysis of 96 samples plus 12 standards (twice) per day.•DMTP was the most abundant dialkyl phosphate in both mothers and children urine. Organophosphate based pesticides are widely used in the agricultural sector, and exposure to these chemicals is common for the general population. Pesticides are toxic due to the inhibition of acetylcholinesterases, and the potential for adverse health effects have been investigated in past and recent studies. Human biomonitoring of organophosphate pesticide exposure is carried out through the determination of the metabolites in urine (dialkylphosphates, DAPs). Hereby we present a new method for determination of the 6 non-specific metabolites dimethyl phosphate (DMP), diethyl phosphate (DEP), dimethyl thiophosphate (DMTP), diethyl thiophosphate (DETP), dimethyl dithiophosphate (DMDTP), and diethyl dithiophosphate (DEDTP) in urine based on off-line solid phase extraction (anion exchange, 96-well plates) followed by ion-pair ultra-performance liquid chromatography time-of-flight mass spectrometry. Recoveries and accuracies in control urine spiked at 5ng/mL ranged from 48% to109% and from 91% to 115%, respectively. The method limits of detection for the DAPs were 1.2ng/mL for DMP, 0.38ng/mL for DEP, 0.20ng/mL for DMTP, 0.33ng/mL for DETP, 0.64ng/mL for DMDTP, and 0.15ng/mL for DEDTP. The method was applied to samples from a Norwegian mother/child study group (n=48/56) and the DAPs detection frequencies in urine from mothers and children were about: 40% for DMP, 95% for DEP, 96% for DMTP, 50% for DETP, 15% for DMDTP, and 1% for DEDTP. In both mothers and children, the most abundant DAPs were DMTP (median 2.4/5.2ng/mL) and DEP (median 2.6/3.4ng/mL) followed by DMP (median 1.5/2.1ng/mL). The SG corrected concentrations of DEP and DETP in mothers were statistically higher than in children (p-value