Comparison of Proposed Response Mechanisms of Precipitate-Based Ion-Selective Electrodes in the Presence of Interfering Ions

New experimental results on nonmonotonic transients are reported here to confirm and extend published results. The new data support the notion that both adsorption/desorption and surface reactions of the crystal membrane are important processes determining transient selectivity coefficients. The former induces local changes in exterior surface concentrations of responsive ions. The latter change the composition of the membrane. Both affect the measured potential. Two proposed models for the response of a precipitate-based Ion-selective electrode (ISE) in the presence of primary and interfering ions are discussed. The mathematical expressions for the models are examined in light of ISE thermodynamics, finite ion-exchange kinetics, and non-steady-state diffusion. The adsorptlon/desorptlon model describes the overshoot/decay portion of the potential-time curves more accurately than the mixed-phase formation model, but a kinetic version of the latter applies at very long times. The combination of the expanded models was shown to describe all features of the experimental curves. © 1989, American Chemical Society. All rights reserved