Titus Zwickl

Steady-State Model Calculations Predicting the Influence of Key Parameters on the Lower Detection Limit and Ruggedness of Solvent Polymeric Membrane Ion-Selective Electrodes

Using a previously described steady-state model, the influence of various parameters on the response function of ion-selective electrodes is investigated. The parameters studied include activities of interfering ions of the sample and inner solution, selectivity coefficients, lipophilicity of the analyte, concentrations of ionophore and lipophilic ionic sites in the membrane, the thickness of the Nernstian diffusion layer and the membrane as well as the diffusion coefficients in both phases. The results obtained provide indications as to how the lower detection limit of potentiometric sensors and their ruggedness can be improved.

Effects of controlled current on the response behavior of polymeric membrane ion-selective electrodes

The influence of external currents on the potential response of polymeric membrane ion-selective electrodes (ISEs) is analyzed theoretically. The treatment is based on the well-established potential model of ISE membranes, extended by contributions from current flow and corresponding electrodialytic ion fluxes through the membrane. A general implicit solution is derived that describes the potential response in terms of the external current, the selectivity characteristics of the membrane, and the compositions of the membrane, the sample solution, and the inner solution, respectively. Explicit relationships are given for limiting cases, e.g. when only one kind of cation is present in the solution or when the disturbance by interfering cations is small. For the latter case, theoretical curves are compared to experimental ones and are shown to give a good correspondence.