Application of a radioactivity detector to the analysis of 14C-Carmoisine metabolites by ion-pair high-pressure liquid chromatography

14C-Carmoisine was incubated under anaerobic conditions with a suspension of human faeces. Analyses of the incubation medium by high-performance liquid chromatography (HPLC) attached to a radioactivity monitor (RAM) showed the same radioactivity profile as the urine and faeces of rats dosed with the same azodye (200 mg kg-1; 25 microCi). The analyses were carried out with a 5 micron RP-C18 chromatographic column, using a linear gradient profile of different concentrations of water, methanol and an ion-pair reagent. Five radioactive peaks were present in the radiochromatogram , in addition to unmodified Carmoisine. The major peak retained half of the specific activity of Carmoisine, and exhibited the retention time and the u.v. spectrum of authentic naphthionic acid. The results demonstrate the value and the advantage of using the in vitro preparation as a model to detect and to identify the metabolites of similar synthetic azodyes used as food additives.