Extraction of nerve agent VX from soils.

The development and optimization of a method allowing the extraction of intact organophosphorus chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) from several types of soils are presented here. This involved the selection of an appropriate buffer to bring the sample to a pH close to the pK(a) of VX but sufficiently low to avoid its basic hydrolysis. Buffering with Tris (pH 9) and subsequent extraction of the aqueous layer by a 85:15 (v/v) hexane/dichloromethane mixture allows rapid and sensitive flame photometric detection of VX at spiking levels lower than 10 microg x g(-1), even after 3 months of aging. Extraction yields were close to 60% in complex matrixes. This method also allows recovery and identification of a characteristic degradation product of VX, bis(2-diisopropylaminoethyl) disulfide, which appears to be formed during the aging process. The performance of this method is far better than that of OPCW reference operating procedure, which does not allow extraction of detectable amounts of VX (spiked at 10 microg x g(-1)) in one of the soils used for this study.