Use of fluorine-doped tin oxide electrodes for lipoic acid determination in dietary supplements

This paper reports a novel application of fluorine-doped tin oxide electrodes (FTO). To this purpose, electrochemical oxidation mechanism of lipoic acid (LA) at different pHs in the presence of interferents was investigated. FTO displayed electroactivity toward LA oxidation at pH 2. The results indicated that interference from water soluble interferents, derived from excipients or other components coming from dietary supplements, is completely removed with the use of FTO. Square-wave voltammetry, SWV, studies have been shown that at pH 2 an anodic peak at about 0.95 V vs. Ag/AgCl, KCl(sat’d) appears. It was also demonstrated that LA oxidation is diffusion-controlled, involving two electrons in the overall process. From these results, a FTO-based electrode was proposed as LA sensor. SWV was the technique of choice for LA quantitation. A linear range between 5 and 500 μmol L−1 was found. These results allowed postulating FTO as a potential candidate for the electrochemical determination of LA in the presence of interferents contained in pharmaceutical samples of supplementary diet.