Extraction of alkyl methylphosphonic acids from aqueous samples using a conventional polymeric solid-phase extraction sorbent and a molecularly imprinted polymer.

The analysis of alkyl methylphosphonic acids (AMPAs) constitutes an important subject for verifying the compliance to the Chemical Weapons Convention (CWC). Indeed, alkyl methylphosphonic acids are the degradation products of V and G nerve agents such as VX, sarin or soman. Lowering the limits of detection of analytical methods for complex aqueous matrices implies the introduction of concentration and clean-up steps in the whole analytical process. Therefore a molecular imprinted polymer (MIP) has been previously developed for the selective extraction and the concentration of the alkyl methylphosphonic acids. Unfortunately, the selective retention process on this MIP has involved the development of hydrogen bonds and so does not allow the direct percolation of aqueous samples. A change of solvent is then necessary and can be performed using solid-phase extraction (SPE) with conventional non selective hydrophobic sorbents. Two polymeric sorbents, Oasis HLB and HR-P resins, were selected for their high specific surface area. The extraction recoveries obtained on both sorbents were compared and the Oasis HLB sorbent was further selected and used for the percolation of acidified aqueous samples. An optimised SPE procedure was then applied to concentrate an aqueous soil extract spiked with isobutyl methylphosphonic acid (iBMPA) and cyclopentyl methylphosphonic acid (cPMPA) that was further cleaned-up by passing through the MIP. The resulting LC-MS full scan chromatograms highlight the clean-up effect of the SPE-MIP association by the removal of the matrix substances and the preservation of 95% of the compounds of interest.

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.