Electrochimica Acta 49 (2004) 3435–3443 From clay- to organoclay-film modified electrodes: tuning charge selectivity in ion exchange voltammetry Ignas K. Tonle a,b , Emmanuel Ngameni b , Alain Walcarius b,∗ a Laboratoire de Chimie Analytique, Faculté des sciences, Université de Yaoundé I, B.P. 812 Yaoundé, Cameroon b Laboratoire de Chimie Physique et Microbiologie pour l’Environnement, UMR 7564, CNRS, Université Henri Poincaré Nancy I, 405, Rue de Vandoeuvre, F-54600 Villers-les-Nancy, France Received 20 January 2004; received in revised form 15 March 2004; accepted 20 March 2004 Available online 30 April 2004 Abstract The surface of two natural smectite-type clay samples was chemically modified by covalent grafting of amine groups, by reaction with -aminopropyltriethoxysilane, which were easily protonated in HCl medium. Multisweep cyclic voltammograms of clay-film modified glassy carbon electrodes made of either the raw clays or the propylammonium-functionalized samples exposed to Ru(NH 3 ) 6 3+ or Fe(CN) 6 3- electroactive probes were obtained. The results indicated a permselective behavior of these clay and organoclay-films based on either favorable or unfavorable electrostatic interactions. The cation-exchanging raw clay film modified electrodes exhibited accumulation properties for Ru(NH 3 ) 6 3+ species while rejecting Fe(CN) 6 3- , whereas the anion-exchanging organoclay coatings acted as a barrier against Ru(NH 3 ) 6 3+ while increasing dramatically the concentration of Fe(CN) 6 3- species at the electrode surface. Strong binding of the probe to the organoclays resulted in a potential shift of ca. 0.1 V of the voltammetric signals characteristic of the Fe(CN) 6 3-/4- couple in the anodic direction. Their good preconcentration efficiency at low analyte concentration highlighted their interest for electroanalytical applications. © 2004 Elsevier Ltd. All rights reserved. Keywords: Clay modified electrodes; Organically modified clays; Ion exchange voltammetry; Clay film; Surface reactivity 1. Introduction The ion exchange voltammetry technique has been de- veloped some 15 years ago by both the Martin’s and Wang’s groups [1,2]. It is based on the concept of chemi- cally modified electrodes, in which the modifier is an ion exchange material most often coated onto the surface of a solid electrode as a charge selective film. The analytical technique takes advantage of the accumulation capabilities of the ionomer coating to enhance concentrations of elec- troactive ionic species at the electrode surface; it has been reviewed by Ugo and Moretto with respect to applications in electroanalysis [3]. Several ion exchange materials were used for that purpose, including a wide range of organic polymers (both polyanionic ionomers [1,2,4–9], polyca- tionic ionomers [6,10] or charged conducting polymers [11–13]), clays [14–18], zeolites [19,20] or silica-based ∗ Corresponding author. Tel.: +33-3-83-68-52-59; fax: +33-3-83-27-54-44. E-mail address: walcariu@lcpe.cnrs-nancy.fr (A. Walcarius). organic–inorganic hybrids [21–25]. Most applications were devoted to the electroanalytical fields, such as trace anal- ysis [13,26–28], electrocatalysis and biosensors [26,29], or for speciation purposes [30,31]. A theoretical model of mass transfer kinetics at such modified electrodes was also provided [32,33]. On the other hand, clay modified electrodes have attracted considerable attention in the past two decades and this field has been thoroughly reviewed [34–40]. Most investiga- tions fall into two main categories: (1) the exploitation of electrochemistry to characterize transport issues of various substances in clays by means of the voltammetric response of electroactive probes located within the layered structure [38], and (2) the design of electrochemical sensors by ex- ploiting the combination of clay properties with selected redox processes [39]. The first direction might contribute to better understanding of pollutant migration in the environ- ment, to help at optimizing soil remediation processes, or to lead to advanced applications involving selective recog- nition or solid/liquid separations. The second category con- cerns mainly the electrochemical quantification of various 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.03.012