ELECTROCHEMICAL-BEHAVIOR OF DOPAMINE AND ASCORBIC-ACID AT OVEROXIDIZED POLYPYRROLE(DODECYL SULFATE) FILM-COATED ELECTRODES

The electrochemical behaviour of dopamine and ascorbic acid at overoxidized polypyrrole(dodecyl sulphate) film-coated glassy carbon electrodes was investigated. It was found that dopamine can be efficiently accumulated into the film and the voltammetric detection limit of dopamine is greatly improved by this procedure. The current response was linear in the concentration range 0.1-10 mu M and a detection limit of 40 nM was achieved when a 2-min preconcentration step under open-circuit conditions was used. A high selectivity for dopamine was observed owing to the exclusion of anionic species by the negative charges in the film. Chronoamperometry and chronocoulometry were used to determine the concentration and diffusion characteristics of dopamine within the film as a function of dopamine concentration in the solution and the film thickness. The film was found to protect the substrate electrode surface from poisoning by the oxidation product of dopamine. Good reproducibility was observed for multiple measurements of dopamine in 0.1 M phosphate buffer solution (pH 7.4).