Determination of Methylphosphonofluoridic Acid in the Environment by Derivatization and LC/MS/MS Analysis

Rapid and specific detection of toxic Novichok agents (A230, A232, A234) is crucial for forensic investigations and the prevention of chemical weapon misuse. While A232 and A234 are relatively stable, A230 is less stable and primarily undergoes hydrolysis via P–F bond cleavage. This product indicates the presence of the Novichok core but does not indicate the agent’s prior existence. In this study, a method with high sensitivity for determining the presence of the minor A230 hydrolysis product—namely methylphosphonofluoridic acid (MPFA), which is generated via P-N bond cleavage—in environmental matrices was established. 2-[(Dimethylamino)methyl]phenol (2-DMAMP) was found to be effective for the derivatization of MPFA in water. The derivatization protocol after optimization involved adding 2-DMAMP followed by agitating for 72 h at 50 °C before LC–MS/MS analysis. The derivatized MPFA, analyzed by ESI–MS/MS, showed two main fragment ions with m/z values of 185.0 and m/z 107.0. The approach was applied to tap water, aqueous soil extract, and saline samples. While intact MPFA exhibited reduced detectability due to strong matrix effects, derivatization enhanced its stability and minimized interferences, resulting in its significantly higher detection sensitivity. The detection of MPFA provides a clear indication that the toxic Novichok compound was present prior to hydrolysis.