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 hydrol ysis products of the organophosphorus nerve agents listed in the Chemi cal 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 p entafluorobenzyl esters. Extremely high sensitivity was obtained and l ow attogram amounts could be detected by GC/NICI-MS. ion-exchange chro matography was employed for selective isolation and enrichment of AMPA in serum, urine, water and soil samples. Collision-induced dissociati on (CID) of the single methylphosphonate anion peak from NICI of the p entafluorobenzyl ester produced fragment ions specific for the methylp hosphonate structure, allowing positive identification of AMPA. CID co nditions optimized far structure information and for sensitivity were investigated. The improved selectivity of GC/MS/MS. allows the detecti on of femtogram amounts of AMPA in samples where chemical background i nhibits detection by GC/MS.