A theoretical model has been developed to simulate the formation of a membrane potential as a function of physically accessible parameters. The description is an extension of the well-known Teorell-Meyer-Sievers (TMS) model, now including free and fixed ionic sites and free and fixed neutral ligands. The model shows that selectivity loss appears as the molar ratio of [ligand]/[ionic site] < 1 in the case of fixed ionic sites. The effect of complete immobilization of the neutral ligand has been simulated by gradually decreasing the mobility ratio α of the cation-ligand complex and free cation in the membrane phase. At lower α, the membrane potential is reduced by a counteracting diffusion potential. This effect is not present if the product of the association constant β1, the total ligand concentration L and α is larger than 104. Furthermore, it is shown that cation permselectivity of ion-selective membranes that contain fixed anionic sites cannot be eliminated by the incorporation of an equal amount of fixed cationic sites.
|Number of pages||21|
|Journal||Journal of electroanalytical chemistry and interfacial electrochemistry|
|Publication status||Published - 1990|