A Comparison of the Electrochemical and Electroanalytical Behavior of Ascorbic Acid, Dopamine and Uric Acid at Bare, Activated and Multi-Wall Carbon Nanotubes Modified Glassy Carbon Electrodes

The electrochemical oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA), as three important biological molecules, have been studied at the bare, activated and multi-wall carbon nanotubes modified glassy carbon electrodes (MWCNT-GCE) using different voltammetric methods. MWCNT-GCE not only exhibited both the roles of mediator and promoter for AA oxidation, but also performed the role of an excellent promoter for electrochemical oxidation of DA and UA when compared with bare GCE (BGCE) or activated GCE (AGCE). The results show that the oxidation of AA at MWCNT-GCE exhibits the characteristic shape typical of an EC catalytic (ErCi') mechanism. In differential pulse voltammetric measurements, MWCNT-GCE and AGCE could separate the oxidation peak potentials of AA, DA and UA present in the same solution, though the MWCNT-GCE remarkably improves the sensitivity of determination of the analytes and also reduces the fouling effects as compared to AGCE. Furthermore, the hydrodynamic amperometry at rotating MWCNT-GCE at constant potential was used for determination of AA, DA and UA individually in the presence of the other two species. It has been shown that using MWCNT-GCE, these three species can be determined by amperometry with high sensitivity and selectivity. Finally, MWCNT-GCE has been applied to simultaneous determination of AA and DA in the related injection solutions and UA in a human urine sample with satisfactory results.