Determination of dialkyl phosphate metabolites of organophosphorus pesticides in human urine by automated solid-phase extraction, derivatization, and gas chromatography-mass spectrometry.

Organophosphorus (OP) pesticides are highly toxic but used commonly worldwide, nevertheless. Their urinary dialkylphosphate (DAP) metabolites are widely used for exposure assessment of OP pesticides in humans. We previously developed an analytical method to measure urinary DAPs utilizing solid-phase extraction (SPE)-derivatization-gas chromatography-tandem mass spectrometry (GC-MS-MS) with quantification using isotope-dilution technique. We now present a more cost-effective yet highly accurate method that can be easily adaptable to many laboratories for routine OP exposure assessment. This method is simple and fast and involves automated SPE of the metabolites followed by derivatization with pentafluorobenzyl bromide and quantification by GC-MS. Dibutyl phosphate (DBP) serves as the internal standard. The detection limits for the six metabolites ranged from 0.1 to 0.15 ng/mL. Depending on the metabolite the relative standard deviation of the analytical procedure was 2-15% for the metabolites. We compared performance of DBP as an internal standard with that of isotope-labeled compounds and found that DBP gives reliable results for the analytical procedure. We also optimized reaction parameters of pentafluorobenzylation.