Free radicals have become very important in recent years due to the damage they cause to biological molecules. The superoxide radical (O₂•-) is the primary species of reactive oxygen species (ROS) that plays a major role in physiological processes. This radical normally is produced physiologically at such a rate that the human body is able to catabolize it. However, when the production of O₂•- radicals exceeds the capacity of the human body, physiological imbalances become harmful.

In this work the xanthine oxidase enzyme is proposed to catalyze the oxidation of xanthine and take advantage of the production of O₂•- radicals. The O₂•- formed in the enzymatic reaction are reacted with different antioxidant compounds (caffeic acid, gallic acid, ascorbic acid) and the oxidized species are quantified by cyclic voltammetry in an electrochemical cell thermostatted at 30 °C in a medium buffered with phosphate buffer 0.1 mol L⁻¹ pH 7.0. A carbon paste electrode was the working electrode, Ag/AgCl the reference and platinum the counter electrode. All antioxidants have an oxidation process between 200 and 600 mV, as well as a reduction process between −200 and 200 mV. The enzyme and the substrate do not present redox processes in the work potentials. However, uric acid has an oxidation process around 400 mV, but does not present reduction processes.