We developed a method that uses electrochemical impedance spectroscopy (EIS) to choose an electrode to determine photosensitizing dye No. 201 (quaternium-73), a thiazolium derivative, in cosmetics. The method is based on nanoparticle metal oxide (tin, cerium, cobalt, iron, and nickel)-modified carbon paste electrodes. Using differential pulse voltammetry (DPV), we found that the electrocatalytic property of tin oxide was better than that of the other metal oxides tested. When the proposed method was used to determine photosensitizing dye No. 201 in commercial cosmetics, the results were were comparable to those obtained using high-performance liquid chromatography with ultraviolet detection.
