Factors affecting the analytical applications of zeolite-modified electrodes preconcentration of electroactive species

The influence of various experimental parameters on the electrochemical response of zeolite-modified electrodes (ZMEs) have been studied using ion-exchange voltammetry, with regard to their application as amperometric sensors. In order to cover a large range of parameters, the investigations were carried out using three zeolites (A, X and Y), selected for their different cation-exchange capacities and ion-sieving properties; four electroactive species (silver(I), copper(II), dopamine and methylviologen) chosen on the basis of their size, charge and inorganic or organic nature; and two kinds of ZMEs: the zeolite-modified carbon-paste electrode (ZMCPE) and the zeolite monograin layers coated on glassy carbon electrode (ZMGCE). Compared to the corresponding unmodified electrodes, improvements in sensitivity were observed when using ZMEs, due to analyte accumulation at the electrodeʹs surface by ion exchange in zeolite particles. The concentration process, and the subsequent voltammetric response of ZMEs, were found to be strongly affected by the accessibility of the analytes to the ion-exchanging sites and their mobility within the zeolite framework. Good correlation was found between results obtained in ion-exchange voltammetry and conventional ion-exchange characterization. The advantage of these fundamental studies for electroanalytical purposes was exemplified for the determination of copper(II) ions, using both ZMCPE and ZMGCE, zeolites A, X and Y, and the following analytical scheme: “preconcentration/voltammetric detection”.