Voltammetric determination of dopamine in the presence of ascorbic acid at over-oxidized polypyrrole-indigo carmine film-coated electrodes.

Over-oxidized polypyrrole films doped with indigo carmine (PPy-IC) offer substantial improvements in voltammetric sensitivity and selectivity towards dopamine. This polymer coating attenuates the voltammetric response of ascorbic acid while the oxidation peak current of dopamine is enhanced by over one order of magnitude compared with that at the bare electrode. The high sensitivity and selectivity for dopamine appears to be mainly due to the charge discrimination and the analyte accumulation. The detection limit is dependent on both film thickness and preconcentration time. At a 0.25 micron thick PPy-IC film-coated electrode, for a 2 min preconcentration time, the detection limit is 10(-8) mol l-1, over two orders of magnitude lower than at a bare glassy carbon electrode. The concomitant ascorbic acid shows no interference although its concentration is as high as 0.1 mmol l-1. The effects of various experimental parameters on the voltammetric response of dopamine were also investigated. The attractive permselective and preconcentrating properties of the PPy-IC films make them valuable for in vivo electrochemistry.