Electron ionization mass spectral studies of a series of <i>N'</i> -trimethylsilyl derivatives of <i>N</i> , <i>N</i> -dialkylacetimidamides

A series of N'- trimethylsilyl (TMS) derivatives of N,N -dialkylacetimidamides (amidines) ( 1 - 10 ) was investigated using gas chromatography-mass spectrometry (GC-MS) under electron ionization (EI) conditions. These amidines are of particular interest as precursors and degradation products of highly toxic Novichok nerve agents and are classified as non-scheduled reportable chemicals under the Chemical Weapons Convention (CWC) by the Organisation for the Prohibition of Chemical Weapons (OPCW). Structural elucidation and identification of the N'- TMS derivatives were achieved through comprehensive analysis of their EI fragmentation patterns. Three sets of isomeric compounds ( 3 – 5 , 6 – 7 , and 8 – 10 ) were successfully distinguished based on characteristic fragmentation pathways and the relative abundances of diagnostic ions. To further support the mass spectral interpretation, retention indices were determined for all analytes in accordance with standardized OPCW protocols. The combined use of EI-MS fragmentation data and retention indices establishes a reliable and robust analytical approach, enabling sensitive and unambiguous identification of these amidines at trace levels in complex environmental matrices following derivatization.