DETERMINATION OF THE MAIN HYDROLYSIS PRODUCT OF O-ETHYL S-2-DIISOPROPYLAMINOETHYL METHYLPHOSPHONOTHIOLATE, ETHYL METHYLPHOSPHONIC ACID, IN HUMAN SERUM

For the unequivocal proof of the use of a nerve agent O-ethyl S-2-diis opropylaminoethyl methylphosphonothiolate (VX), a rapid, accurate and sensitive method which allows us to identify its main hydrolysis produ ct ethyl methylphosphonic acid (EMPA) in human serum was explored by G C-MS. GC-MS analysis was performed after solvent extraction with aceto nitrile in acidic conditions from the serum sample, which was previous ly deproteinized by micro-ultrafiltration, and subsequent tert.-butyld imethylsilyl derivatization with N-methyl-N-(tert.-butyldimethylsilyl) tri (MTBSTFA) with 1% tert.-butyldimethylsilyl chloride (t-BDMSC). Lin ear calibration curves were obtained in the concentration range from 5 0 to 500 ng/ml for EMPA in the full-scan EI mode and from 5 to 50 ng/m l for EMPA in the SIM EI mode. The relative standard deviation obtaine d at a sample concentration of 50 ng/ml was 8.4% in the full-scan mode and 7.3% in the SIM mode. Upon applying the full-scan EI and CI mode, 40 ng/ml and 80 ng/ml were the detection limits. Using the SIM-EI mod e, in which the ion at m/z 153 was chosen, the limit was 3 ng/ml.