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

Carbon paste electrodes modified with several types of copper-doped zeolite s were evaluated as sensors for nonelectroactive cations in a Bow injection system. After having described the amperometric detection mechanism and pr oposed 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 catio nic species), such as the applied potential, mobile phase composition and f low rate, the ionic strength of the sample solution, or the injection volum e. The analysis was then extended to other mono- and divalent cations and s electivity series were established in relation to wherever zeolites A, X, Y , or clinoptilolite was used. It was concluded that the sensor's response w as 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 ob tained for the analysis of alkali metal, ammonium, calcium and magnesium io ns using the copper-doped zeolite Y modified electrode in a 0.01 M tetrabut ylammonium bromide mobile phase. (C) 1999 Elsevier Science B.V. All rights reserved.