Development of ionoselective electrochemical sensors by using the sol–gel process

Electrochemical sensors based on electrodes modified with entrapped ion-exchange polymers using the doping sol–gel method has been developed. Poly (dimethyldiallylammonium chloride) (PDMDAAC) or poly(vinylsulfonic acid, sodium salt) (PVSA) has been used as anionic and cationic ion exchangers respectively. Spectroscopic grade graphite electrodes were modified with the polymer–sol–gel solution obtained, and characterised by square wave voltammetry (SWV) using Fe (CN)64 for the anionic exchange polymer and methyl viologen dichloride (MVDC) for the cationic exchange polymer. The process take place in two independent stages, providing the most adequate medium (pH, ionic strength) in the selective preconcentration and in the measurement steps; increasing in this way selectivity and sensibility of the developed sensors. Modified electrodes give detection limits two and three orders of magnitude (for the cationic and anionic polymer respectively) lower than the analogous graphite electrodes. Furthermore, the polymer–sol–gel electrode surfaces were easily renewed by reversing the ion-exchange reaction. Shrinking/swelling effects of films deposited in the electrode surfaces as well as leaching out of polymers from the sol–gel were not observed. Good reproducibility of the analytical procedures developed were also obtained.