Reversed-phase LC determination of two manufacturing intermediates, the unsulfonated subsidiary color, and 4-methyl-Sudan I in D&C Red No. 6, D&C Red No. 7, and their lakes.

A reversed-phase liquid chromatographic (LC) method was developed to determine 4 impurities in the monosulfo monoazo color additives D&C Red No. 6, D&C Red No. 7, and their lakes. Manufacturing intermediates determined are 2-amino-5-methylbenzenesulfonic acid (PTMS) and 3-hydroxy-2-naphthalenecarboxylic acid (3-hydroxy-2-naphthoic acid). Subsidiary colors determined are the unsulfonated and uncarboxylated, unsulfonated homologs of the dye (the unsulfonated subsidiary color and 4-methyl-Sudan I). The new method uses lithium oxalate as part of a novel system to dissolve the water-insoluble color additives. The 4 impurities were identified by LC and UV-visible spectrophotometry; the 4-methyl-Sudan I was confirmed by LC/mass spectrometry. LC peak area calibrations were generally linear (R > 0.999), and recoveries ranged from 90 to 105%. The limits of determination used were 0.02% each for PTMS and 3-hydroxy-2-naphthoic acid, 0.1% for the unsulfonated subsidiary color, and 0.002% for 4-methyl-Sudan I. The relative standard deviations at the specification levels ranged from 0.7 to 22.7%. Survey analyses of 26 samples of certified D&C Red Nos. 6 and 7 straight colors and lakes from 11 domestic and foreign manufacturers yielded results that agree with those previously obtained using 3 other methods.

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.