On the Electrochemical Oxidation of Dopamine, Ascorbic Acid and Uric Acid onto a Bare Carbon Paste Electrode from a 0.1 M NaCl Aqueous Solution at pH 7

From cyclic voltammetry, CV, and differential pulse voltammetry, DPV, the dopamine, DA, ascorbic acid, AA, and uric acid, UA, electrochemical behavior were studied using a bare carbon paste electrode, CPE, immersed in a 0.1 M NaCl aqueous solution (pH 7). The results proved that DA, AA and UA oxidation were all diffusion-controlled processes. For DA, from CV experiments, the heterogeneous standard rate constant, k0, and energy transfer coefficient, a, were evaluated as 0.008 cm2s-1 and 0.45 respectively however, for AA and UA these parameters could not be measured because in both cases, during the cathodic potential scan no significant currents were detected, thus both oxidation processes are irreversible. From the DPV recorded in the system CPE / 0.1 M NaCl at pH 7 at different DA, AA or UA concentrations, it was possible to note that for all the cases that the peak current varied linearly with the DA, AA or UA concentration, thus all these substances can be electrochemically quantified when they are not mixed. In agreement with the results obtained, it could be observed that the bare CPE is more sensitive (23.79 ± 0.04 μAmM-1) toward the UA, as compared with the DA and AA, and that the lower detection limit (5.63 ± 0.01 μM) was also reached for UA.