Simultaneous Scanning Electrochemical Microscopy and UV-Vis Absorption Spectroelectrochemistry.

The combination of instrumental techniques allows obtaining precise and reliable information about the reactions taking place at the electrode/solution interface. Although UV-Vis absorption spectroelectrochemistry (UV-Vis SEC) provides a molecular insight about the species involved in the electrode process, obtaining information about the redox state of the products generated in this process is not always accessible by this technique. In this sense, scanning electrochemical microscopy (SECM) has a clear advantage, since it provides additional information on the oxidation state of the intermediates/products. Therefore, the combination of these two techniques facilitates obtaining a more complete picture of the electrochemical reaction studied from two different points of view, but under exactly the same experimental conditions. In this work, the combination of UV-Vis SEC in parallel configuration and SECM is carried out for the first time. This new technique allows distinguishing between those species that are electrochemically active and, at the same time, exhibit changes in the UV-Vis absorption spectra during the electrochemical reaction. The new experimental setup is first validated using ferrocenemethanol as a standard probe, concomitantly obtaining spectroscopic and electrochemical information that accurately describes the oxidation process. Finally, the strength of this combined technique is demonstrated by studying the antioxidant activity of -vanillin (-HVa) in the presence of electrogenerated superoxide. The information extracted from the new UV-Vis SEC/SECM technique makes it possible to identify, beyond any doubt, not only the origin of the electrochemical signals recorded in the SECM tip but also to evaluate the antioxidant effect of -HVa at different concentrations.