Reversed phase ion-pairing HPLC-ICP-MS for analysis of organophosphorus chemical warfare agent degradation products

Abstract

The separation and analysis of three organophosphorus chemical warfare degradation products is described. Ethyl methylphosphonic acid (EMPA, the major hydrolysis product of VX), isopropyl methylphosphonic acid (IMPA, the major hydrolysis product of Sarin (GB)), and methylphosphonic acid (MPA, the final hydrolysis product of both) were the analytes and were separated by reversed phase ion-pairing high-performance liquid chromatography (RP-IP-HPLC) with the use of myristyl trimethylammonium bromide as ion-pairing reagent and an ammonium acetate–acetic acid buffer system (pH 4.85). An Agilent 7500ce inductively coupled plasma mass spectrometer (ICP-MS) equipped with collision/reaction cell technology was coupled to the chromatographic system for detection of ³¹P and ⁴⁷PO⁺. Historically, ICP-MS detection of phosphorus has been limited due to its high first ionization potential (10.5 eV) and the presence of severe nitrogen polyatomic interferences (such as ¹⁴N¹⁶O¹H⁺ and ¹⁵N¹⁶O⁺) overlapping its only isotope at m/z = 31. Implementation of an octopole reaction cell with helium as the cell gas allowed for removal of the nitrogen polyatomic interferences and reduction of background signal. Detection limits for EMPA, IMPA, and MPA were found to be 263, 183 and 139 pg mL⁻¹, respectively, with separation in less than 15 min. The developed method was successfully applied to the analysis of spiked environmental water and soil samples.