Electrochemical studies on a pharmaceutical azo dye: Tartrazine

Tartrazine (trisodium salt of 3-carboxy-5-hydroxy-1-p-sulfophenyl-4-p-sulfophenylazopyrazole) was selected as the model compound for this study because of its wide application in various pharmaceutical formulations either as such or in combination with some other dyes as color additives. A well-defined single cathodic peak was obtained at -0.535 V. In the acidic pH region, two cathodic peaks were obtained that merged into a single peak at higher pH. Controlled-potential electrolysis (CPE) at -1.20 V reduced peak current from -90.00 to -2.00 muA with a considerable decrease in color and absorbance. The rate of decrease of the current and absorbance was found to exhibit a first-order dependence. The COD of the solution showed a decrease from 1080 to 560 mg/L. No peak could be observed in the voltammograms after CPE, indicating the absence of any electroactive substance left in the solution. Electrochemical reduction of tartrazine results in the formation of the hydrazono derivative in a two-electron reduction pathway.