Electrochimica Acta 49 (2004) 573–580 Electrochemical behavior of an anion-exchanger modified electrode prepared by sol–gel processing of an organofunctional silicon alkoxide Cheng-Li Lin, Pei Tien, Lai-Kwan Chau ∗ Department of Chemistry and Biochemistry, National Chung Cheng University, Ming-Hsiung, Chia-Yi 621, Taiwan, ROC Received 28 May 2003; received in revised form 19 August 2003; accepted 3 September 2003 Abstract Sol–gel films prepared from quaternary amine functionalized silicon alkoxide precursor on electrode surfaces have been investigated as anion-exchange and permselective coatings for electroanalytical investigations. These modified electrodes were evaluated with Fe(CN) 6 3- and Ru(bpy) 3 2+ as the analytes using cyclic voltammetry. At low solution pH, the anionic analyte preconcentrated within the functionalized sol–gel coating and resulted in an improvement in detection limit of about 2 orders of magnitude compared to bare electrodes, but the response for the cationic analyte was suppressed. The modified electrodes are rugged and reproducible and can be regenerated. We have also shown that the anion-exchange and permselective properties of the modified electrodes can be affected by the composition, concentration, and pH of the support electrolyte. © 2003 Elsevier Ltd. All rights reserved. Keywords: Sol–gel; Anion-exchange; Ion-exchange voltammetry; Chemically modified electrode; Permselective coating 1. Introduction Electrodes modified with thin films of ion-exchange ma- terials has given rise to a new analytical technique named ion-exchange voltammetry [1,2], which takes advantage of the preconcentration capabilities of the coating for elec- troactive ionic species. Today, most anion-exchangers are organically based, which typically have high exchange ca- pabilities but limited permeability and poor film adhesion. On the other hand, silica presents attractive properties such as thermal stability, durability with organic solvents and oxi- dizing agents, rigidity, and ease of surface modification with a variety of functional groups. As such, organically modified anion-exchangers based on silica matrix combine the phys- ical properties of the glass, with the exchanging properties of the organic functional groups [3–9]. Recently, the field of silica-modified electrodes has been reviewed [10–13]. The sol–gel process is very well adapted for coating of thin films on complex shapes [7,14,15]. The porosity and pore size of these films can be controlled [16–18]to maxi- mize the specific surface area and to ensure that permeability ∗ Corresponding author. Tel.: +886-5-2720411x66411; fax: +886-5-2721040. E-mail address: chelkc@ccu.edu.tw (L.-K. Chau). of the film remain high. Furthermore, the sol–gel process in- volves low-temperature hydrolysis and condensation of ap- propriate monomeric precursors and is suitable for inclusion of organic moieties that cannot withstand high temperatures. Recently, anion-exchange glasses have been produced by en- trapment of organic anion-exchange compounds [3] or poly- meric anion-exchangers [4] in sol–gel glasses or by sol–gel processing of an organofunctional silicon alkoxide precur- sor [5–9]. Some of these sol–gel materials have been used to modify electrode surfaces [4–7,9]. Collinson and coworkers exploited the anion-exchange and permselective properties of a modified electrode based on a coating prepared from sol–gel processing of a primary amine alkoxysilane [5,6]. However, primary amine is a weak base anion-exchanger and is only usefully functional at low pH since hydroxide ion has a very high affinity on such weak base anion-exchangers and hence it dominates the ion-exchange process at high pH by its high concentration and high affinity [19]. In this paper, we report on the fabrication and use of an organically modified sol–gel material as both anion- exchange and permselective coatings for electroanalytical investigations. The material, named propyl-N,N,N-trimethyl- ammonium functionalized silica (PTMAFS), incorporates a quaternary ammonium functional group, propyl-N,N,N- trimethyl-ammonium (PTMA), which is linked to the silica 0013-4686/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2003.09.011