New Insights Into Electron Impact Mass Spectral Fragmentation of Restricted Aromatic Amines

Many primary aromatic amines are powerful human carcinogens, which are occasionally found in adulterated food, textile and leather products and dyes. Gas chromatography (GC) coupled with electron impact (EI) mass spectrometry is a commonly used technique for their analysis. Although EI mass spectrometry is widely used for the analysis of primary aromatic amines, information on their fragmentation patterns remains limited, and no comprehensive review has systematically compiled and discussed the available literature. In this work, a comprehensive survey of mass spectral fragmentation of restricted primary aromatic amines through EI ionization is presented with previously reported fragment ions. Mass spectral fragmentation patterns of listed banned aromatic amines are presented, with the most prominent and representative ions addressed and discussed with structures. Variation in fragmentation is explained by examples of structurally similar compounds. The fragmentation of similar aromatic amines has also been discussed comparatively using electrostatic potential mapping. Special consideration has been given to isomer discrimination, taking the example of xylidine isomers, employing statistical algorithms such as independent t-test, k-nearest neighbours and peak intensity ratio analysis of significant peaks. The stabilities of the product fragments have also been accounted for and explained. The aromatic amines mostly fragment predominantly via pathways leading to the formation of cyclopenta-1,3-diene ion, tropylium ions, phenyl cations or their derivatives. Nitrogen is predominantly eliminated from precursor ions as hydrogen cyanide. Most aromatic amines exhibit prominent molecular ion peaks in their mass spectra. The fragmentation patterns of compounds with additional functional groups such as chloro, methoxy, azo and nitro groups have also been discussed.