Voltammetric behavior and determination of tocopherol in vegetable oils at a polypyrrole modified electrode

The voltammetric behavior of alpha-tocopherol in the presence of vegetable oil is studied at a polypyrrole modified Pt electrode in a 1,2-dichloroethane-ethanol medium with cyclic voltammetry. Cyclic voltammogram of alpha-tocopherol showed a well-defined oxidation peak; the peak potential shifting toward less positive and a much higher peak current obtained at a polypyrrole modified electrode than that obtained at the unmodified Pt electrode. An electroanalytical method for the determination of alpha-tocopherol based on its electrochemical oxidation at the polypyrrole modified Pt electrode is developed. Using differential pulse voltammetry, the peak currents were found to increase linearly with the alpha-tocopherol concentration over the range of 5.0 to 300 mu M, with a sensitivity of 5.38 x 10(-2) A L mol(-1) and the limit of detection of 1.5 mu M (S/N = 3), the detection time being about 90 s for each assay. The interference of other synthetic antioxidants such as TBHQ, BHA and BHT to the analysis of cc-tocopherol was investigated. The developed method is applied to the quantification of tocopherols in six vegetable oils, showing that the results are in good agreement with those by HPLC method.