A series of N,N-dialkylacetimidamides (amidines) (1–10) are designated as non-scheduled reportable chemicals under the Chemical Weapons Convention by the Organisation for the Prohibition of Chemical Weapons (OPCW). The amidines are relevant precursors and degradation products of highly toxic Novichok nerve agents. These amidines and their methyl derivatives (11–20) were systematically investigated under electron ionization (EI) mass spectral conditions. These compounds showed molecular ions with considerable abundance in their mass spectra. Each amidine was identified and characterized based on its characteristic fragmentation pattern. Among these, the possible six sets (3–5; 6 & 7; 8–10 and 13–15; 16 & 17; 18–20) of structural isomers were distinguished unambiguously using their fragmentation pattern and ion intensities. Additionally, retention indices were determined for all the analytes by following the OPCW work instructions. The combined EI mass spectral data and retention indices provide reliable identification of these amidines at trace levels in complex environmental matrices.
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