Characterization of amines by Fast Black K salt in thin-layer chromatography

Abstract

Amines were characterized on a silica gel thin-layer chromatographic (TLC) plate with the diazonium reagent Fast Black K salt (FBK) and with subsequent novel procedures: acid treatment or treatment with N-(1-naphthyl)ethylenediamine in acid solution. The differentiation of primary, secondary and tertiary aliphatic and aromatic amines was demonstrated, with special attention to drug substances. By using the N-(1-naphthyl)ethylenediamine treatment a 5-fold improvement in the detection limits for aliphatic secondary amines was achieved compared with FBK alone, allowing detection of 0.01 µg of methamphetamine and 0.04 µg of methyl phenidate. The structures of the coloured reaction products were elucidated by spectroscopic and TLC methods. An unexpected reaction was observed with dialkylanilines, which reacted by N-coupling with various diazonium salts with cleavage of an alkyl group.