Rapid and Sensitive Quantitative Analysis of Alkyl Phosphates in Urine after Organophosphate Poisoning

Abstract

Organophosphate compounds are widely used as pesticides. After ingestion by humans, organophosphates decompose into alkyl phosphates. Decomposition continues postmortem. We developed a rapid ("3 h), quantitative, and sensitive analysis of the human organosphosphate metabolites O,O-dimethylphosphate (DMP), O,O-diethylphosphate (DEP), O,O-dimethylthiophosphate (DMTP), O,O-diethylthiophosphate (DETP), O,O-dimethyldithiophosphate (DMDTP), and O,O-diethyldithiophosphate (DEDTP). Urine is dried under azeotropic conditions with isopropanol and nitrogen. All metabolites are converted into their corresponding benzyl esters reacting with benzyl bromide and diazotoluene. The protocol prevents the isomerization of DMTP and DETP occurring when diazo compounds are used exclusively. The benzyl ester derivatives are purified on solid-phase extraction silica columns. The quantitative analysis is performed by gas chromatography-mass spectrometry. All metabolites can be identified by the parent molecular ions. Urine samples from eight cases of fatal suicidal poisoning dialkyl phosphates were quantitated. The limits of detection ranged from 3 to 6 ng/mL. Hence, this protocol is sufficiently sensitive to detect and quantitate organophosphate metabolites beyond cases of fatal poisoning, in the clinical setting, and even following average environmental exposure.