Trace determination of alkyl methylphosphonic acids in environmental and biological samples using gas chromatography/negative-ion chemical ionization mass spectrometry and tandem mass spectrometry

Alkyl methylphosphonic acids (AMPA) are metabolites and primary hydrolysis products of the organophosphorus nerve agents listed in the Chemical Weapons Convention (CWC). Gas chromatography/negative‐ion chemical ionization mass spectrometry and tandem mass spectrometry (GC/NICI‐MS and GC/NICI‐MS/MS) were used for the determination of AMPA as their pentafluorobenzyl esters. Extremely high sensitivity was obtained and low attogram amounts could be detected by GC/NICI‐MS. Ion‐exchange chromatography was employed for selective isolation and enrichment of AMPA in serum, urine, water and soil samples. Collision‐induced dissociation (CID) of the single methylphosphonate anion peak from NICI of the pentafluorobenzyl ester produced fragment ions specific for the methylphosphonate structure, allowing positive identification of AMPA. CID conditions optimized for structure information and for sensitivity were investigated. The improved selectivity of GC/MS/MS allows the detection of femtogram amounts of AMPA in samples where chemical background inhibits detection by GC/MS.