Determination of Dialkyl Phosphates in Human Urine using Gas Chromatography-Mass Spectrometry

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Abstract
Organophosphates are used as pesticides in agriculture and pest control. They are metabolized to dialkylphosphates, which are excreted in urine. Determination of these metabolites is useful for assessing human exposure to organophosphates. This publication describes a new, reliable, and very sensitive analytical procedure for quantitating dimethylphosphate (DMP), diethylphosphate (DEP), O,O-dimethylthiophosphate (DMTP), O,O-diethylthiophosphate (DFTP), O,O-dimethyldithiophosphate (DMDTP), and O,O-diethyldithiophosphate (DEDTP) in human urine. The analytes are extracted from acidified urine into a mixture of diethylether and acetonitrile. Dibutylphosphate serves as internal standard. Derivatization is performed using pentafluorobenzylbromide at 40°C overnight. After further liquid-liquid extraction, analysis is carried out by gas chromatography-mass spectrometry. The limits of detection are 5 µg/L urine for DMP and 1 µg/L for the other five metabolites. Using the new procedure, 54 spot urine samples from persons in the general population in Germany were analyzed. Nearly every sample contained DMP, DEP, and DMTP, and the median values (95th percentiles) of the concentrations were 30 µg/L (105 µg/L), 4 µg/L (21 µg/L), and 22 µg/L (174 µg/L), respectively. DETP and DMDTP were found in lower concentrations.

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