Differentiation of isomeric methylanilines by imidization and gas chromatography/mass spectrometry analysis

Rationale Carcinogenic o -methylaniline is one of the banned aromatic amines in azo dyes, but it is very difficult to distinguish it from its noncarcinogenic isomers due to their identical retention time on chromatography and similar mass spectra. Methods Imidization of the isomeric methylanilines was carried out by treatment with benzaldehyde under mild conditions. The formed derivatives were analyzed by gas chromatography/mass spectrometry (GC/MS). Theoretical calculations were carried out on the Gaussian 03 program by using the density functional theory method at the B3LYP/6-311+G(d,p) level. Results Imidization of methylanilines occurred easily and gave rise to the corresponding N -methylbenzylidene benzenamines. The isomeric derivatives were completely separated by GC, and thus the three isomeric methylanilines could be determined simultaneously. Due to the ortho effect, the derivative from o -methylaniline has a characteristic fragment ion at m/z 118 with a stable bicyclic structure, and it could be easily differentiated from the meta - and para -isomers in electron ionization mass spectrometry. Conclusions These results provided a promising solution for simultaneous determination of isomeric methylanilines.