THE ELECTROCHEMISTRY OF NEUROTRANSMITTERS AT CONDUCTING ORGANIC POLYMER ELECTRODES : ELECTROCATALYSIS AND ANALYTICAL APPLICATIONS

The electrooxidation of catechols, catecholamines and NADH at conventional electrode materials is generally characterized by high degrees of irreversibility as well as strong adsorption and, hence, fouling by reactants and/or products of the reactions. On the contrary, the rates of the electron transfer are highly catalysed by the use of conducting polymer films, such as poly(3-methylthiophene), polyphenylene, polyanaline and polypyrrole, as described here. Furthermore, the usual fouling problems are eliminated. Even interference from electroinactive large proteins, such as haemoglobin, and other surfactants are substantially reduced. Also, electron spectroscopy for chemical analysis, energy-dispersive analysis of X-rays, theoretical diffusion coefficient calculations, metal ion coordination, solution diffusion analyses of cyclic voltammograms etc. show that the electron transfer occurs at the polymer-solution interface and not at the inert electrode substrate surface after diffusion through the polymer matrix or through pores. The analytical application of these polymer electrodes as amperometric detectors for flow injection analysis and high performance liquid chromatography are given. In addition, selective potentiometric electrodes for catecholamines based on conducting polymer films of crown ethers, such as binaphthyl-20-crown-6, dibenzo-18-crown-6, etc., have been developed and characterized. These potentiometric detectors significantly decrease the usual interferences of ascorbic acid, uric acid and acetaminophen found in amperometric detection.