Analysis of nerve agent degradation products in high-conductivity matrices by transient ITP preconcentration and CZE separation coupled to ESI-MS

Preconcentration of nerve agent degradation products (alkyl methylphosphonic acids) contained in high-conductivity matrices was performed using transient ITP to enhance sensitivity of CE-ESI-MS. The separation conditions of the five studied alkyl methylphosphonic acids in CE-MS were first optimized. The presence of methanol in the separation medium was required to obtain a good separation of the analytes under counter-EOF conditions. Preconcentration by ITP was induced by the BGE acting as leading electrolyte (LE) while the terminating electrolyte (TE) was loaded before the sample because of the counter-EOF conditions. Different leading ions (formate or acetate) and LE concentrations were tested. The best results for the analysis of soil extracts fortified with the analytes were obtained with an LE composed of 30 mM CH₃COONH₄ adjusted to pH 8.8 with ammonium hydroxide in (35:65 v/v) MeOH/H₂O mixture. The TE consisted of 200 mM glycine adjusted to pH 10.0 with ammonium hydroxide in the same solvent mixture. The loading length of the TE zone was optimized. The initial pH of the TE, which determined the initial mobility of the terminating ion, appeared to markedly influence the resolution and the sensitivity. This transient ITP-CZE-MS method was then adapted for the analysis of rat urine samples fortified with the analytes, which required the use of a more concentrated LE (50 mM). LODs between 4 and 70 ng/mL in soil extract, and between 5 and 75 ng/mL in rat urine were reached from extracted ion electropherograms.