Atmospheric and electrochemical oxidation of ascorbic acid in anionic, nonionic and cationic surfactant systems

It is well known that the antioxidant activity of some species in homogenous solutions may not be the same as that in heterogeneous media. This environment dependence is the reason for investigating ascorbic acid antioxidant activity in surfactant solutions. In our study we have investigated the kinetics of atmospheric oxidation and electrochemical oxidation of ascorbic acid in aqueous solutions of the four surfactants: SDS, AOT (anionic), TRITON-100 (nonionic), and CTAB (cationic). For each surfactant the concentrations below and above CMC were investigated. As expected, a general trend in the atmospheric oxidation rate changes in the following manner: the micellar solution of nonionic surfactant shows a faster oxidation rate than that of the anionic surfactant, and the cationic surfactant an even higher one. The more subtle effects were observed with each surfactant concentration change. The influence of the surfactants on the electrochemical behavior of ascorbic acid was also studied. A general conclusion emerging from our investigation is that surfactants shift the ascorbic acid oxidation potential and change the peak current value. This phenomenon is due mainly to the surfactant film formed at the electrode/solution interface.