Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quantitatively related to equilibria at the interface between the sample and the electrode membrane. However, only correctly determined selectivity coefficients allow accurate predictions of ISE responses to real-world samples. Moreover, they are also required for the optimization of ionophore structures and membrane compositions. Best suited for such purposes are potentiometric selectivity coefficients as defined already in the 1960s. This paper briefly reviews the basic relationships and focuses on possible biases in the determination of selectivity coefficients. The traditional methods to determine selectivity coefficients (separate solution method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For example, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coefficients may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to determine correct potentiometric selectivity coefficients unaffected by such biases is presented.

Selectivity of potentiometric ion sensors.

Neutral Carrier Based Ion-Selective Electrodes

This review focuses on the more significant contributions to the understanding and use of ion-selective electrodes (ISE's). There is a strong interest in this field as over 1400 articles and abstracts were found during the writing of this review which covers the period from January 1986 through December 1987. The major analytical and electrochemical journals were read and a hand search of Chemical Abstracts uncovered the remaining articles. Unlike previous fundamental reviews, this paper will not attempt to list all the pertinent papers on ISE's. Rather, the more interesting works and applications are covered to illustrate examples of the general trends and directions of ISE interests.

Ion-Selective Electrodes.

Speciation of Lead in Contaminated Soils

Potentiometric pH selective tips for scanning electrochemical microscopy (SECM) have been developed and used to image local pH changes in a variety of model chemical systems. Images of pH profiles around a platinum microelectrode during water reduction, a corroding disk of silver iodide in aqueous potassium cyanide, a disk of immobilized urease hydrolyzing urea, and a disk of immobilized yeast cells in glucose solution were obtained. A simple method for fabricating antimony microdisk electrodes suitable for use in SECM is described. The general theory for SECM with potentiometric ion selective tips is also present, assuming that the tip is a purely passive sensor

G. Horvai

Papers

Injection techniques in dynamic flow-through analysis with electroanalytical sensors

A simple continuous method for calibration and measurement with ion-selective electrodes

An evaluation of some commercial lead(II)-selective electrodes

Theoretical models of ion-selective electrode membranes

Effect of pH on the response of a cyanide ion-selective electrode