Identification of acidic degradation products of chemical warfare agents by methylation with trimethylsilyldiazomethane and gas chromatography–mass spectrometry

Sensitive and reliable analysis of alkylphosphonic acids (APAs) and 2-( N,N- dialkylamino)ethanesulfonic acids (SAs), the degradation products of chemical warfare agents (CWAs), is one of the most important tasks for verification of the Chemical Weapons Convention (CWC). Unambiguous identification of these chemicals is required in a variety of environmental matrices, including soil and water. These acids with low volatility are very polar, and efficient and reliable methylation methods for their derivatization are needed for analysis with gas chromatography–mass spectrometry (GC–MS). In this study, the derivatization conditions for trimethylsilyldiazomethane (TMSDAM) methylation were optimized for rapid GC–MS screening. Optimized methylation of APAs and SAs with TMSDAM was compared with methylation with diazomethane. The TMSDAM methylation of SAs and benzilic acid was further compared with silylation with N -methyl- N -( tert -butyldimethylsilyl)trifluoroacetamide. The significance and necessity of cation exchange prior to derivatization and analysis were tested on samples with a high inorganic background. A recommendation to use the method for methylation of water samples and aqueous extracts using TMSDAM is given. The robustness of the method was illustrated by the successful identification of APAs and SAs in aqueous samples from proficiency tests organized by the Organisation for the Prohibition of Chemical Weapons.