A selective voltammetric method for uric acid detection at Nafion(R)-coated carbon paste electrodes.

A square-wave voltammetric method together with Nafion(R)-coated carbon paste electrodes were used for the selective determination of uric acid in the presence of a high concentration of ascorbic acid. Since the oxidation potential of uric acid is about 200 mV more positive than that of ascorbic acid at the Nafion(R)-coated carbon paste electrode, the selectivity can be greatly improved simply by applying an electrolysis potential of +0.4 V vs. Ag/AgCl where only ascorbic acid is oxidised. The acceptable tolerance of ascorbic acid concentration for the determination of uric acid is as high as 1.5 mM. With 30 s of electrolysis time, a linear calibration curve is obtained over the 0-50 muM range in 0.05 M citrate buffer solution, pH 4.0, with slope (muA/muM) and correlation coefficient of 0.34 and 0.9984, respectively. The detection limit (3sigma) is 0.25 muM. The practical analytical utility is illustrated by selective measurements of uric acid in human urine without any preliminary treatment.