Simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid by methylene blue adsorbed on a phosphorylated zirconia–silica composite electrode

This paper describes the preparation, characterization and application of a composite electrode based on methylene blue adsorption to phosphorylated zirconia–silica mixed oxide particles prepared by a sol–gel process. This electrode electrocatalytically oxidizes ascorbic acid (AA), dopamine (DA) and uric acid (UA), allowing their simultaneous voltammetric detection. Well-defined and -separated oxidation peaks were observed by differential pulse voltammetry in a 0.35 mol l−1 Tris–HCl buffer solution (pH 7.4) containing 0.5 mol l−1 KCl. The anodic peak currents observed at −74, 94 and 181 mV increased with increasing concentrations of AA, DA and UA, respectively. Linear calibration plots were obtained over the range of 100–1600 μmol l−1 for ascorbic acid, 6–100 μmol l−1 for dopamine and 22–350 μmol l−1 for uric acid with detection limits of 8.3 ± 0.1, 1.7 ± 0.1 and 3.7 ± 0.2 μmol l−1, respectively. DA and UA concentrations could also be determined under conditions of excess AA (1 mmol l−1).