Determination of carmoisine and its unsulphonated product in mixtures by solid-phase spectrophotometry

A new spectrophotometric method for simultaneous determination of Carmoisine and its corresponding unsulphonated product in mixture is proposed. The method is based on the selective fixation of the sulphonated colorant Carmoisine on Sephadex DEAE A-25 gel at pH 1.5 and of its unsulphonated product (1-naphthylazo-1-naphthol) on C-18 silica gel at pH 5.0 and the subsequent measurement of the absorbances in solid-phase. The applicable concentration ranges were 12.0-650.0 mu g L-1 for Carmoisine and 2.0-100.0 mu g L-1 for unsulphonated product, the volumes of sample being 100 mi, and 500 mi, respectively. Detection limits were 3.38 and 0.56 mu g L-1 respectively. The method was applied to the determination of both chemicals in foods and in synthetic colorants used as raw material in the manufacturing of foods, drugs and cosmetics.