IMPROVEMENT OF POTENTIOMETRIC SELECTIVITY OF ION-EXCHANGER BASED MEMBRANES DOPED WITH CO-EXCHANGER - ORIGIN OF THE EFFECT

A novel equation is derived to describe the electric potential and sel ectivity of membranes which contain ion-exchanger and some co-exchange r. Numeric simulation of the potentials and that of concentrations of species in the membranes allows elucidation of the origin of the co-ex changer effect on potentiometric selectivity. It is shown that the eli mination of the diffusion potential due to addition of co-exchanger is the main source of the beneficial effect of such additives. Another i mportant feature of these membranes is the stabilization of the concen tration of free ion-exchanging sites and their excess relative to ions . As a result, the potentiometric selectivity of membranes doped with co-exchanger becomes proportional to the association selectivity of io n-exchanging sites. (C) 1998 Elsevier Science S.A. All rights reserved .