Influence of EDTA on the electrochemical behavior of phenols Rosangela M. de Carvalho, Lauro T. Kubota, Susanne Rath * Institute of Chemistry, UNICAMP, P.O. Box 6154, 13083-970, Campinas SP, Brazil Received 17 October 2002; received in revised form 12 February 2003; accepted 28 February 2003 Abstract Electrochemical oxidation of phenolic compounds leads to a deposition of polymeric films on the surfaces of Pt, glassy carbon, pyrolytic graphite and carbon fiber electrodes, decreasing the electrode activity (passivation). Addition of EDTA to the medium produces a significant enhancement in the electrochemical behavior of phenolic compounds, avoiding electrode passivation. An improvement in the selectivity and sensitivity for the quantitative voltammetric determination of dopamine, catechol and 4- aminophenol was also verified. The electroactivity of the electrode was maintained even after long periods of use in the presence of EDTA. The effect of the EDTA concentration on the electrochemical behavior of some phenolic compounds is reported. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Phenol; EDTA; Inhibition of electrode passivation; Electrochemical behavior 1. Introduction The loss of the electrode activity during phenol oxidation, as well as with other aromatic organic compounds, is well documented in the literature [1]. Fichter and Ackerman [2], as early as the last century, reported that surface films are formed during anodic oxidation of some aromatic compounds with a subse- quent instability and a loss of precision in further electroanalytical measurements. Although this phenom- enon was described a long time ago, no practical solution for the effective inhibition of film formation has been proposed. The electrochemical oxidation of phenolic com- pounds can induce the inactivation of electrodes, via deposition of electropolymerized films, which are formed when phenoxy radicals attack an unreacted substrate. The accumulation of reaction products, which leads to the loss of electrode activity, is commonly referred as ‘poisoning’ or ‘fouling’ [3 /5]. Babai and Gottesfeld [6] have studied these polymeric films using ellipsometric measurements in order to follow the growth of films formed on the surface of platinum electrodes by the electrooxidation of phenolic compounds in aqueous solutions. These polymeric films, with a thickness between 100 and 1000 A ˚ , are porous and their chemical composition is not regular. Gattrell and Kirk [7] have also studied such films produced on a platinum electrode during phenol oxidation in an aqueous acidic solution. These authors verified that, in the inner Helmholtz layer, phenol is irreversibly ad- sorbed as the oxidation involves ring cleavage. At the outer Helmholtz layer, rapid oxidation with minimal rearrangement of the reactant molecules occurs. The flow of the initial current is due to the reactions taking place in the outer Helmholtz layer and this current continues until the unreactive products block these reactions and the slower inner layer reactions begin to predominate. Some procedures have been described attempting to diminish the problems caused by these films, but they are questionable in practice for routine electroanalysis. Cellophane membranes or Nafion † polymer films are employed to cover the electrode surface for the purpose of retarding the loss of electrode activity [5]. The application of membrane */covered electrodes for am- perometric analysis results in a loss of sensitivity because the transport of the analyte through the membrane is slow in relation to the mass transport in solution. * Corresponding author. Tel.:  /55-19-3788-3084; fax:  /55-19- 3788-3023. E-mail address: raths@iqm.unicamp.br (S. Rath). Journal of Electroanalytical Chemistry 548 (2003) 19  /26 www.elsevier.com/locate/jelechem 0022-0728/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0022-0728(03)00193-1