From clay- to organoclay-film modified electrodes: tuning charge selectivity in ion exchange voltammetry

The surface of two natural smectite-type clay samples was chemically modified by covalent grafting of amine groups, by reaction with γ-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.