Development of a Highly Sensitive ³¹P{¹H} NMR-Based Method for Trace-Level Detection of Alkylphosphonic Acids as...

Nerve agents with P-C linkage, viz. sarin, soman, cyclosarin, VX, Novichok A-230, and their analogues are highly toxic in nature and produce alkylphosphonic acids (APAs) upon environmental degradation. The Organization for the Prohibition of Chemical Weapons (OPCW) has enlisted APAs with C₁-C₃ P-C linkages under Schedule 2.B.04 of the Annex of the Chemical Weapons Convention (CWC). Detection of APAs at trace levels (<10 ppm or 10 μg/mL), as environmental markers of such deadly nerve agents, is a very perplexing task under CWC verification analysis. During Official Proficiency Tests (OPTs), OPCW mandates the detection of all CWC-related chemicals in test samples at ≥1 μg/mL levels. As of now, there is no method available to detect APAs at such low concentration levels through NMR spectroscopy. Complex environmental matrices and the low sensitivity of NMR in comparison to mass spectrometric techniques (GC-MS and LC-MS) are the major hurdles in the verification of APAs through NMR. Herein, we report a highly sensitive NMR method for the detection of APAs in complex environmental matrices using a room temperature broadband observe probe. The method relies on K₂CO₃-assisted deprotonation of APAs to obtain their ³¹P{¹H} NMR signatures at trace levels in aqueous matrices. The key experimental approach of the developed method is unique and in line with the requirements of OPTs of OPCW, with an achievable detection limit of APAs at ≥1.0 μg/mL levels in complex environmental matrices. The developed method is of great relevance, especially in CWC verification and forensic analysis of APAs at trace levels.