Simultaneous determination of uric acid and ascorbic acid using glassy carbon electrodes in acetate buffer solution

The present work reports the simultaneous determination of uric acid (UA) and ascorbic acid (AA) in 0.2 M, pH 4.0, acetate buffer solution using glassy carbon (GC) electrode by square wave voltammetry. Selective detection of UA in the presence of 200-fold excess of AA is achieved at the GC electrode in acetate buffer solution. The GC electrode separates the voltammetric signal of UA from AA by 310 mV and the signals observed for these two compounds at GC electrode in acetate buffer was highly stable and reproducible. In contrary, the simultaneous determination of AA and UA in 0.1 M, pH 7.2, phosphate buffer solution can not be achieved due to the fouling effect caused by the adsorption of oxidized product of AA on the electrode surface. The stable and reproducible results obtained at GC electrode for the simultaneous determination of AA and UA in acetate buffer solution suggest that the GC electrode does not undergo surface fouling in acetate buffer solution. In contrast, gold and platinum electrodes fail to distinguish the oxidation peaks of AA and UA in phosphate buffer solution whereas these electrodes could separate the oxidation of UA from AA by 260 mV in acetate buffer solution but the results are not reproducible. The GC electrode can detect as low as 1 mu M of UA in the presence of large concentration of AA with excellent reproducibility. The sensitivity of GC electrode towards UA was found to be 18.57 A mu M-1 cm(-2), which is nearly 5 times higher than towards AA (3.57 A mu M-1 cm(-2)). The practical application of the present system is demonstrated by measuring the concentration of UA in human urine samples without any treatment. (c) 2005 Elsevier B.V. All rights reserved.