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 1000 ng/ml DMMP in acetonitrile were employed. Through 15 calibration curves using the 5 lowest concentrations, coefficient of determination (r2) 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 1000 ng/ml) yielded a mean r2 of 0.997 (0.991–1.000). Sixty-five nitrogen diluted gaseous samples varying from 1.0 to 10.0 μl in volume were analyzed and concentrations of DMMP ranging from 1 to 1000 ng/ml were confirmed. An additional 35 vapor samples in UHP N2 ranging in DMMP concentration from 5.8 μg/m3 to 1.0 mg/m3 were analyzed by increasing sample volume range to between 10.0 and 100 μl. For gaseous samples with volumes > 1.0 μl, the lowest concentration observed was 5.8 μg/m3. The method detection limit (Appendix B of Title 40 CFR, United States) for 1.0 μl autoinjected standards in acetonitrile was determined to be 0.331 ng/ml. Method precision for 15 independently analyzed standards of 25 ng/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.