Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)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 mu mol l(-1) for ascorbic acid, 6-100 mu mol l(-1) for dopamine and 22-350 mu mol l(-1) for uric acid with detection limits of 8.3 +/- 0.1, 1.7 +/- 0.1 and 3.7 +/- 0.2 mu mol l(-1), respectively. DA and UA concentrations could also be determined under conditions of excess AA (1 mmol l(-1)). (c) 2008 Elsevier Ltd. All rights reserved.542560565Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [00/11103-5]