Polyaniline-modified electrode as an amperometric ascorbate sensor

Electrochemical oxidation of ascorbate at polyaniline-modified electrode has been studied. The autocatalytic reaction mechanism has been proposed for anodic oxidation of ascorbate in nearly pH-neutral buffered solutions: protons liberated during ascorbate oxidation cause a local pH drop within a thin polyaniline layer, turning it into a proton-doped conducting form that shows electrocatalytic activity towards oxidation of ascorbate. The proposed mechanism explains the ability of polyaniline to electrocatalyze the anodic oxidation of ascorbate even in pH-neutral solutions, where polyaniline presents in its undoped and non-conducting form. It has been shown that polyaniline-modi tied electrodes can be used for ascorbate assay within a pH range of 5.5-7.2, operating potential window of 0.1-40 V versus Ag/AgCl, showing a linear range of response up to 0.6 mM, and a lower detection limit of 0.05 mM. (c) 2004 Elsevier B.V. All rights reserved.