Rapid derivatisation of novichok precursor amidines for improved detection by GC-MS.

Recently, the Annex on Chemicals of the Chemical Weapons Convention was amended to include four new entries to the Schedule 1 toxic chemical list. These new entries included the novichok agents A-230, A-232 and A-234. In addition to this, 17 N,N-dialkyl(alkan)imidamides precursor chemicals were added to various export control lists. These additions increased the population of chemicals that could require reporting during both the Organisation for the Prohibition of Chemical Weapons (OPCW) Official Proficiency Test (PT) and authentic sample analysis. The network of OPCW Designated Laboratories (DL) therefore needs to be aware of these newly listed chemicals, their precursor chemicals and degradation products and associated chromatographic and mass spectral properties. N,N-Dialkyl(alkan)imidamides often exhibit poor gas chromatography properties and require derivatisation prior to analysis. Complicating this is the difficulty in silylating N,N-dialkyl(alkan)imidamides in aqueous environments, in addition to the inherent instability of the subsequent silyl ester. Therefore, derivatising agents that readily react with N,N-dialkyl(alkan)imidamides to form derivatives with improved GC-MS properties and are stable for extended time periods are of importance to DLs. A possibility to address these twin concerns is derivatising with an alkyl chloroformate using modified Schotten-Baumann conditions to form the corresponding carbamate. Using these conditions, a series of N,N-dialkyl(alkan)imidamides were derivatised with methyl chloroformate and assessed for an improvement to both their GC-MS behaviour and stability. Additionally, samples from the 56th and 57th OPCW Official PT, spiked with N,N-diisopropylethanimidamide and N-methyl-N-propylethanimidamide respectively, were treated with methyl chloroformate. Significant improvements in stability and chromatographic properties were observed in all instances.