Time-Dependent Phenomena in the Potential Response of Ion-selective Electrodes Treated by the Nernst−Planck−Poisson Model. 1. Intramembrane Processes and Selectivity

Abstract

The variability of selectivity coefficients, resulting from potential changes over time and the concentration ratio of primary to interfering ions, impedes many practical applications of ion-selective electrodes (ISEs). Existing theoretical interpretations of ISE selectivity are restricted by severe assumptions, such as steady state and electroneutrality, which hinder theorizing on this problem. For this reason, for the first time, the Nernst-Planck-Poisson equations are used to predict and visualize the selectivity variability over time and the concentration ratio. Special emphasis is placed on the non-Nernstian response in the measurements with liquid-ion-exchanger- and neutral-carrier-based ISEs. The conditions under which measured selectivity coefficients are true (unbiased) are demonstrated.

Theory and computer simulation of the time-dependent selectivity behavior of polymeric membrane ion-selective electrodes

“…Virtual experiments of this kind were reported earlier and were found to yield hysteresis phenomena depending on the direction of activity changes [23]. It has to be pointed out that the time-dependent effects shown in Figure 4 are in good agreement with results obtained in real experiments [22].…”

“…Hence, the results of these approaches may be less suited for treating time-dependent response phenomena. A recent extended theory based on a combined Nernst-Planck-Poisson model for the ion fluxes is indeed capable of describing the time-dependent behavior of ISEs [22]. On the other hand, it requires a very complex numerical procedure to calculate the respective response data.…”

A solid-contact Pb2+-selective polymeric membrane electrode with Nafion-doped poly(pyrrole) as ion-to-electron transducer

“…However, the conventional polymeric membrane electrodes with the inner filling solutions suffer from ion fluxes of primary ions between the inner aqueous solution and the sample solution, which may deteriorate the lower detection limits [3] and the selectivity coefficients of the ISEs [4]. Many empirical approaches have been used to decrease these ion fluxes including adjusting the composition of the inner solution [5,6], lowering the concentration of ionic sites, and increasing the thickness and polymer content of the membrane [7].…”

Comparison of different approaches to the description of the detection limit of ion-selective electrodes

“…An approach, based upon this idea and dedicated to the general description of ISE behaviour, was later developed [6][7][8][9].…”