Determination of alkylmethylphosphonic acids, the main metabolites of organophosphorus nerve agents, in biofluids by gas chromatography mass spectrometry and liquid-liquid-solid-phase-transfer-catalyzed pentafluorobenzylation

A simple gas chromatography-mass spectrometry (GC-MS) procedure has been developed for the main metabolites of organophosphorus nerve agents, alkylmethylphosphonic acids (AMPAs; alkyl = Et, i-Pr, and pinacolyl) in biofluids via extractive pentafluorobenzylation. The derivatization was carried out under liquid-liquid-solid-phase-transfer conditions using a polymer-bound tri-n-butylmethylphosphonium bromide as a catalyst. AMPAs in aqueous samples were semiquantitatively extracted into a small-volume organic layer as their pentafluorobenzyl derivatives at pH 4.5 (85°C). Sample pretreatments for urine, serum, and saliva were each examined to minimize matrix interference. The detection limits of APMAs by electron-impact ionization GC-MS were around 50 ng/mL and 2.5-10 ng/mL in the full-scan and selected-ion monitoring modes, respectively. In order to detect trace-level AMPAs, negative-ion chemical ionization (NICI) was also employed to enhance sensitivity. The detection limits of AMPAs in biofluids were typically 60 pg/mL by GC-NICI-MS.