Determination of 2,4,6-triiodoresorcinol and other side reaction products and intermediates in the colour additive FD&C Red No. 3 (erythrosine) using high-performance liquid chromatography.

An HPLC method was developed for the quantitative determination of 2,4,6-triiodoresorcinol (I3R), 2-(2',4'-dihydroxy-3',5'-diiodobenzoyl)benzoic acid, resorcinol, phthalic acid, and sodium iodide in the colour additive FD&C Red No. 3 (erythrosine) (R3). Due to the fast decomposition of I3R in aqueous solutions, the dye portions analysed were dissolved in methanol and the determinations were performed in the freshly-made solutions. The HPLC method is rapid (50 min total analysis cycle, approximately 16 min to detect I3R and the other intermediates), simple to implement, and generates only small amounts of solvent waste. It was found to be applicable for use in routine batch-certification as shown by the analysis of test portions from 24 lots of R3 submitted for US-certification by domestic and foreign manufacturers during the past three years.