Gold leaf electrodes for UV/Vis spectroelectrochemical determination of ortho-diphenols in extra virgin olive oil

A simple and easily replicable technique is here presented for assembling planar electrochemical cells based on gold-leaf electrodes using ordinary tools and a do-it-yourself approach. These devices have been profitably used to perform spectroelectrochemical measurements in the reflectance mode demonstrating for the first time how the use of gold-leaf electrodes can offer a viable and low cost alternative to traditionally used electrochemical platforms assembled by gold vapor deposition or screen printing. After optimization of fabrication parameters, the electrochemical and spectroelectrochemical characterization of these cells was performed by using potassium hexacyanoferrate(II) as redox probe. Then, hydroxytyrosol has been selected as model to develop an innovative and so far never presented spectroelectrochemical method for the determination and quantification of ortho-diphenol antioxidants in extra virgin olive oil. The results achieved allowed us to preliminary evaluate the electrochemical oxidation mechanism of hydroxytyrosol at gold leaf electrodes and then to select the best wavelength for its spectroelectrochemical determination. The approach developed enabled to evaluate hydroxytyrosol concentrations from both the electrochemical and spectroscopic signals with repeatable and comparable results. Comparison between electrochemical and optical determinations performed on real sample demonstrates that the two methods can be used indistinctively, proving that spectroelectrochemistry represents an autovalidated technique able to provide reliable results thanks to complementary information that are simultaneously obtained from electrochemistry and spectroscopy.