J. Electroanal. Chem., 188 (1985) 85-94 85 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands ION EXCHANGE AND TRANSPORT OF NEUROTRANSMI'VFERS IN NAFION FILMS ON CONVENTIONAL AND MICROELECTRODE SURFACES G. NAGY *, G.A. GERHARDT, A.F. OKE, M.E. RICE and R.N. ADAMS ** Department of Chemistry, University of Kansas, Lawrence, KS 66045 (U.S.A.) R.B. MOORE, III, M.N. SZENTIRMAY and C.R. MARTIN ** Department of Chemistry, Texas A&M University, College Station, TX 77843 (U.S.A.) (Received 27th September 1984) ABSTRACT Very small Nation-coated vohammetric electrodes are very advantageous for in vivo detection of catecholamine neurotransmitters. In this study their quantitative characteristics with regard to partition- ing of the catecholamines into the Nation film have been studied. The properties of these electrodes have been compared with larger graphite electrodes covered with Nation film. INTRODUCTION In the last decade surface-moditied solid electrodes have become a major focus of electrochemical studies [1] and polymer film-modified electrodes have been of particular interest [2-9]. The Nation polymers have proved to be well suited for preparation of modified electrodes and results of fundamental studies of both the dynamics of charge transport [3-8] and the thermodynamics of ion exchange reactions [4,9] in Nation films at solid electrode surfaces have been reported. We have been examining Nation films deposited on miniature graphite electrodes which can be used to detect neurotransmitter-related species in rat brain [10]. The neuro- transmitters are dopamine (DA), norepinephrine (NE) and 5-hydroxytryptamine (5-HT). All are cations at physiological pH and a Nation-coated voltammetric electrode, with its cation exchange properties, has excellent response to them. On the other hand, biogenic amine metabolites and the important brain substance ascorbic acid are anions or neutral at pH 7.4, so a Nation-coated electrode is practically insensitive to them. This differentiation of the primary amine neurotransmitters * Present address: Institute for General and Analytical Chemistry, Technical University of Budapest, Budapest, Hungary. **To whom correspondence should be addressed.