The surface of two natural smectite-type clay samples was chemically modified by covalent grafting of amine groups, by reaction with gamma-aminopropyltriethoxysilane, which were easily protonated in HCl medium. Multisweep cyclic voltammograms of clay-film modified classy carbon electrodes made of either the raw clays or the propylammonium-functionalized samples exposed to Ru(NH3)(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(NH3)(6)(3+). species while rejecting Fe(CN)(6)(3-), whereas the anion-exchanging organoclay coatings acted as a barrier against Ru(NH3)(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 food preconcentration efficiency at low analyte concentration highlighted their interest for electroanalytical applications. (C) 2004 Elsevier Ltd. All rights reserved.