TO THE PROBLEM ON THE OXIDATION MECHANISM OF AZO DYES ON MODIFIED CARBON-PASTE ELECTRODES

Abstract

In the current study, using a carbon-paste electrode modified with β-cyclodextrin oligosaccharide, the oxidation mechanism of some useful food azo dyes as Sunset Yellow FCF, Tartrazine, Allura Red AC, Carmoisine, Ponceau 4R was established. Cyclic voltammetry was used to investigation redox behaviour of studied food azo dyes (Sunset Yellow FCF, Tartrazine, Allura Red AC, Carmoisine, Ponceau 4R). It was established that such dyes as Sunset Yellow FCF and Ponceau 4R are oxidized quasi-reversibly, and such as Tartrazine, Carmoisine and Allura Red AC are completely irreversibly oxidized. It was noted that for all dyes, except Tartrazine, after oxidation on a cyclic voltammogram, a new reversibly redox pair is formed. This may indicate the formation of new electroactive fragments during the oxidation of azo dyes (Sunset Yellow FCF, Allura Red AC, Carmoisine, Ponceau 4R). Based on the conducted studies of the effect of pH and scanning rate on the oxidation potential of studied azo dyes, it was established that 2 electrons and 1 proton participate in the oxidation process for all dyes, except for Carmoisine, for which oxidation takes place with the participation of 1 proton and 1 electron. Based on the obtained information, as well as using information from our previous studies on the redox behavior of azo dyes (Sunset Yellow FCF, Tartrazine, Allura Red AC, Carmoisine, Ponceau 4R) on carbon-paste electrode modified by silica impregnated with cetylpyridinium chloride cationic surfactant, a scheme for the oxidation of azo dyes was proposed. According to the scheme, oxidation takes place with the participation of an irreversible chemical reaction, which leads to the further rearrangement of bonds with the breaking of the azo group of dyes and the formation of new electroactive fragments.