Determination of Carmoisine, Allura red and Ponceau 4R in sweets and soft drinks by Differential Pulse Polarography

Carmoisine (E 122), Ponceau 4R (E 124) and Allura red (E 129), are synthetic azo dyes 7generally used to give red colour to syrups, soda and sweets. They could be easily distinguished from the natural dyes, which are not electroactive, using differential pulse polarography. The influence of the pH on the intensities and the potentials of the peaks was studied between pH 3 and 11, and acidic or strongly basic media appeared not convenient. It was shown that in a pH=9 phosphate buffer, the peaks of Carmoisine, Allura red and Ponceau 4R were well shaped and separated, allowing accurate identification and quantification, even if the three dyes were mixed. No significant changes of the peak potentials were noticed in the commercial samples, and consequently the dyes can be identified without ambiguity. A procedure using the standard addition technique was validated with test syrups. The recovery was in the 96-105% range and the relative standard deviation was close to 1% for the three dyes. The limits of quantification in the polarographic cell, estimated from the polarographic data, were 42, 43 and 34 μg L^-1 for Carmoisine, Allura red and Ponceau 4R, respectively. The method was applied to commercial soft drinks and sweets. The results were compared to those obtained using liquid chromatography, and they appeared to be in good agreement.