Factors affecting the analytical applications of zeolite modified electrodes: indirect detection of nonelectroactive cations

Carbon paste electrodes modified with several types of copper-doped zeolites were evaluated as sensors for nonelectroactive cations in a Bow injection system. After having described the amperometric detection mechanism and proposed an efficient procedure to achieve good reproducibility in successive measurements, it was shown how various experimental parameters influenced the quantitative determination of potassium ions (chosen as reference cationic species), such as the applied potential, mobile phase composition and flow rate, the ionic strength of the sample solution, or the injection volume. The analysis was then extended to other mono- and divalent cations and selectivity series were established in relation to wherever zeolites A, X, Y, or clinoptilolite was used. It was concluded that the sensor's response was mainly governed by the diffusion of both the electron transfer co-factor (Cu2+ species) and the cationic analytes, rather than by the thermodynamic predictions related to ion exchange equilibrium despite the fact that the amperometric detection was allowed to occur only after the exchange of Cu2+ species for the cationic analyte. Detection limits around 10(-6) M were obtained for the analysis of alkali metal, ammonium, calcium and magnesium ions using the copper-doped zeolite Y modified electrode in a 0.01 M tetrabutylammonium bromide mobile phase. (C) 1999 Elsevier Science B.V. All rights reserved.