Electrocatalytic characteristics of uric acid oxidation at graphite–zeolite-modified electrode doped with iron (III) M. Mazloum Ardakani a, * , Z. Akrami a , H. Kazemian b , H.R. Zare a a Department of Chemistry, Faculty of Sciences, Yazd University, Safa-ieh, Pejoohesh Street, Yazd, Iran b Jaber Ibn Hayan Research Labs, Atomic Energy Organization of Iran, Tehran, Iran Received 28 February 2005; received in revised form 16 September 2005; accepted 20 September 2005 Available online 25 October 2005 Abstract A new method is developed for the catalytic oxidation of uric acid at graphite–zeolite-modified electrode doped with iron (III) (Fe 3+ Y/ZCME). Iron (III) exchanged in zeolite Y act as catalyst to oxidize uric acid. First, the electrochemical behavior of iron (III) incorporated in the zeolite Y-modified electrode was studied. The results illustrate that diffusion controls the ferric/ferrous redox process at the Fe 3+ Y/ZCME. Then, the behavior of electrocatalytic oxidation reaction for uric acid has researched. The charge transfer coeffi- cient (a) for uric acid was calculated as 0.51. The electrode was employed to study electrocatalytic oxidation of uric acid, using cyclic voltammetry, rotating disk electrode and chronoamperometry as diagnostic techniques. The rate constant for the catalytic reaction (k) was also determined by above methods. The diffusion coefficient of uric acid was 1.54 · 10 6 cm 2 s 1 . A linear calibration graph is obtained over the uric acid concentration range of 0.1–10.0 mM. Finally, it has been shown that using the Fe 3+ Y/ZCME, UA can be estimated by amperometry with high sensitivity and good limit of detection by high level of stability of electrode. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Electrocatalytic oxidation; Modified electrode; Fe 3+ Y/ZCME; Uric acid 1. Introduction Chemically modified electrodes (CMEs) have recently attracted much attention [1–6]. They are characterized by a chemically altered surface displaying new qualities that can be exploited for electrochemical purposes. Zeolite- modified electrode (ZMEs) form a subcategory of the chemically modified electrodes, which were largely studied [7,8]. There are three major reasons why ZMEs are interest- ing. The first is that they combine the advantages of ion ex- change voltammetry with unique molecular sieving properties of the zeolite. One can therefore distinguish be- tween the reactants small enough to diffuse freely within the zeolite framework, and excluded from (or occluded in) the structure, and thus, not directly involved in the mass transport reactions. The second reason is linked to the development of new electro analytical devices (sensors). By combining the attractive properties of zeolites (size selectivity, ion exchange capacity, high thermal and chem- ical stability) with the high sensitivity of modern electro- chemical techniques, improvements should be observed as compared to the other sensors based on chemically modi- fied electrodes. The third reason for investigating ZMEs is related to their possible use in electrocatalysis. Zeolites attract interest for this application because they offer a selectivity based on the size (and shape) of the reactants, together with a three-dimensional lattice made of intercon- nected cages of molecular dimension coming in a variety of support sites for various catalysts. Although studies of ZMEs focus mainly on preparation methods of the modi- fied electrode, electrochemical characterization of ion ex- change and the electrode process, as well as discussion of electron transfer mechanism [9,10], a few articles have 0022-0728/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2005.09.015 * Corresponding author. Tel.: +98351821064; fax: +983518211670. E-mail address: mazloum@yazduni.ac.ir (M.M. Ardakani). www.elsevier.com/locate/jelechem Journal of Electroanalytical Chemistry 586 (2006) 31–38 Journal of Electroanalytical Chemistry