Negative ion chemical ionization GC/MS-MS analysis of dialkylphosphate metabolites of organophosphate pesticides in urine of non-occupationally exposed subjects

Low level exposure to organophosphate (OP) pesticides can be determined by the measurement of dialkylphosphate (DAP) metabolites in urine. An analytic al method is presented here which can measure the metabolites dimethyl phos phate (DMP), diethyl phosphate (DEP), dimethyl thiophosphate (DMTP), dimeth yl dithiophosphate (DMDTP), diethyl thiophosphate (DETP), and diethyl dithi ophosphate (DEDTP) at low levels. This was achieved by lyophilization of th e urine, derivatization with pentafluorobenzyl bromide (PFBBr) and quantifi cation by negative ion chemical ionization GC/MS-MS. The detection limits f or the metabolites were 0.5 mug L-1 DMP, 0.1 mug L-1 DEP, 0.1 mug L-1 DMTP, 0.04 mug L-1 DMDTP, 0.04 mug L-1 DETP and 0.02 mug L-1 DEDTP. The RSD for the analytical method was 4-14% for the six metabolites. The method was use d to monitor a group of non-occupationally exposed individuals in Sydney, A ustralia. The metabolites DMP, DEP, DMTP, DMDTP, DETP and DEDTP occurred in 73, 77, 96, 48, 100 and 2% of the samples with median values of 13, 3, 12, <1, 1 and 1 mug L-1 respectively. The method is simple to use, sensitive a nd suitable for routine analysis of non-occupational exposure levels. These detection limits are between one and two orders of magnitude lower than th ose previously reported in the literature.