Theoretical Interpretation of Transient Signals Obtained with Precipitate-Based Ion-Selective Electrodes in the Presence of Interfering Ions

Precipitate-based ion-selective electrodes respond to sudden changes in the interfering ion activity with nonmonotonic, overshoot-type transient signals, when a certain amount of primary ion is also present in the solution and when the respective selectivity factor is much less than one. A simplified and more detailed quantitative description of these signals is presented in terms of diffusion processes in the adherent solution layer and of adsorption/desorption equilibria on the electrode membrane surface. The validity of this description is proved by excellent fittings to experimental signals in cases of (I) increasing and decreasing interfering ion activity steps, (ii) subsequent changes in interfering ion activity, (Hi) interfering ion activity steps at different primary ion activity levels. The selectivity factor, the diffusion layer thickness values, and the amount of ions adsorbed or desorbed providing good fitting were in agreement with the experimental values determined by other methods, within the respective experimental and calculation errors. © 1985, American Chemical Society. All rights reserved