Tandem capillary column gas chromatography-mass spectrometric determination of the organophosphonate nerve agent surrogate dimethyl methylphosphonate in gaseous phase.

A procedure based on capillary column gas chromatographic-mass spectrometric (GC-MS) confirmation was developed for the verification of the ubiquitous and versatile chemical and nerve agent simulant, dimethyl methyl phosphonate (DMMP; CAS# 756-79-6), from gaseous samples. This method was developed to verify low nanogram DMMP concentrations during testing of a nerve agent detection system. Standard solutions of 1, 5, 10, 50, 100, 500, and 1000ng/ml DMMP in acetonitrile were employed. Through 15 calibration curves using the 5 lowest concentrations, coefficient of determination (r(2)) values showed a mean of 0.998 (0.992-1.000). An additional 15 calibration curves likewise containing 5 concentrations of DMMP spanning 3 orders of magnitude (1, 50, 100, 500, and 1000ng/ml) yielded a mean r(2) of 0.997 (0.991-1.000). Sixty-five nitrogen diluted gaseous samples varying from 1.0 to 10.0microl in volume were analyzed and concentrations of DMMP ranging from 1 to 1000ng/ml were confirmed. An additional 35 vapor samples in UHP N(2) ranging in DMMP concentration from 5.8microg/m(3) to 1.0mg/m(3) were analyzed by increasing sample volume range to between 10.0 and 100microl. For gaseous samples with volumes>1.0microl, the lowest concentration observed was 5.8microg/m(3). The method detection limit (Appendix B of Title 40 CFR, United States) for 1.0microl autoinjected standards in acetonitrile was determined to be 0.331ng/ml. Method precision for 15 independently analyzed standards of 25ng/ml had a relative standard deviation of 1.168. This method demonstrated high linearity across a wide range of concentrations, as well as excellent sensitivity and repeatability, and proved applicable to other lower alkyl-phosphonates.