A selective voltammetric method for uric acid and dopamine detection using clay modified electrodes

Electrochemically preanodized clay-modified electrodes were used for the detection of uric acid or dopamine in the presence of a high concentration of ascorbic acid by square wave voltammetry. The major obstacle of the overlapped oxidation potential of ascorbic acid could be overcome through the distinct ability of uric acid and dopamine to coordinate with the electrochemically preanodized clay-modified electrodes. The selective sensing of dopamine is further improved by the charge-exclusion and preconcentration features of Nafion. Linear calibration curves are obtained for 0.5-10 and 10-100 mu M uric acid with 30 s preconcentration time in 0.1 M, pH 1.0 citrate buffer and for 0-6 mu M dopamine in 0.1 M, pH 7.4 phosphate buffer with 20 s preconcentration time. The detection limits (3 sigma) are 0.2 mu M and 2.7 nM for uric acid and dopamine, respectively. The practical analytical utility is illustrated by selective measurements of uric acid in human urine without any preliminary treatment.