Electrochemical Behavior of Graphite Electrodes Modified by Spin-Coating with Sol−Gel-Entrapped Ionomers

Abstract

Tetraethoxysilane sol−gel doped with poly(dimethyldiallylammonium chloride) (PDMDAAC) and poly(vinylsulfonic acid, sodium salt) (PVSA) has been prepared to provide a simple method to produce electrodes coated with new ion-exchange glasses. Electrochemical sensors prepared by spin-coating spectroscopic grade graphite rods with these sol−gel ionomers have been developed. Sol−gel-modified electrodes were evaluated with Ru(bipy)32+ and Fe(CN)64- as analytes using square wave voltammetry. The results indicate a porous coating where diffusion of the analyte through the sol−gel film to the electrode surface occurred. Analyte preconcentration within the polymer-modified sol−gel network resulted in an improvement in detection limits of 1−2 orders of magnitude compared to bare electrodes. The sol−gel−PDMDAAC-modified electrodes give a linear calibration curve for Fe(CN)64- from 1 × 10-6 to 1 × 10-4 M and a detection limit of 7 × 10-7 M. The response could be reproduced at different electrodes with an 18% relative standard deviation at a concentration level of 1 × 10-6 M. At the sol−gel−PVSA-modified electrodes, the calibration curve for Ru(bipy)32+ was linear from 2.8 × 10-7 to 2.8 × 10-4 M, the detection limit was 2 × 10-7 M, and the relative standard deviation was 10% for different electrodes at a concentration level of 2.8 × 10-7 M. Organic ion-exchangers incorporated into a silicate matrix combine the physical properties of the glass, such as thermal stability, negligible swelling effects, tunable porosity, and polar microenvironment, with the ion-exchanging properties of the organic functional group.