Electrochemical properties of a tetrabromo-p-benzoquinone modified carbon paste electrode.: Application to the simultaneous determination of ascorbic acid, dopamine and uric acid

The electrochemical study of a tetra bromo-p-benzoquinone modified carbon paste electrode (TBQ-MCPE), as well as its efficiency for electrocatalytic oxidation of ascorbic acid, dopamine and uric acid, is described. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various solution pH values and at various scan rates. Three linear segments were found with slope values of -58.4 mV/pH, -28.1 mV/pH and 0.0 mV/pH in the pH range 2.0-7.1, pH 7.1-9.0 and pH 9.0-11.0, respectively. The apparent charge transfer rate constant, k(s), and transfer coefficient, a, for electron transfer between TBQ and CPE were calculated as 3.79 +/- 0.10 s(-1) and 0.55, respectively. The electrode was also employed to study the electrocatalytic oxidation of AA, using cyclic voltammetry, chronoamperometry and differential pulse voltammetry as diagnostic techniques. It has been found that the oxidation of AA at the surface of TBQ-MCPE occurs at a potential of about 430 mV less positive than that of an unmodified CPE. The diffusion coefficient of AA was also estimated using chronoamperometry. The kinetic parameters such as the electron transfer coefficient, alpha, and heterogeneous rate constant, k(h)', for oxidation of AA at the TBQ-MCPE surface was determined using cyclic voltammetry. Differential pulse voltammetry (DPV) exhibits two linear dynamic ranges and a detection limit of 0.62 mu M for AA. In DPV, the TBQ-MCPE could separate the oxidation peak potentials of AA, DA and UA present in the same solution, though at the unmodified CPE the peak potentials were indistinguishable. This modified electrode was quite effective not only to detect AA, DA and UA, but also in simultaneous determination of each component concentration in the mixture. (c) 2004 Elsevier B.V. All rights reserved.