Identification and simultaneous determination of Azorubin, Allura red and Ponceau 4R by differential pulse polarography: application to soft drinks

Azorubin (E 122), Ponceau 4R (E 124) and Allura red (E 129), are the most used red dyes in soft drinks manufacturing, and in some cases two dyes are present. The aim of this work is to show that using differential pulse polarography, it was possible to distinguish these synthetic dyes from the natural dyes providing from fruits. In addition, in an appropriate supporting electrolyte, identification and quantitative analysis of these three red dyes were possible, even when they were mixed. Various electrolytes were tested such as potassium chloride, which is a classical supporting electrolyte, citric acid which is one of the components of the soft beverages, sodium citrate and a phosphate buffer. It was shown that the peak intensities and potentials, and consequently their resolution, depend greatly on the pH values. In potassium chloride and sodium citrate the peaks of Azorubin, Allura red and Ponceau 4R were well separated and dyes were identified without ambiguity. Buffer solutions with pH close to 8 and 9 appeared to be appropriate, as the potentials and the intensities of the peaks were slightly changed when small amounts of soft drinks, usually at pH close to 3, were introduced in the cell. A procedure using the standard addition technique was developed, tested with model syrups and then applied to commercial syrups, soda and non-alcoholic bitters. (C) 2002 Elsevier Science B.V. All rights reserved.