Influence of the dielectric constant of the medium on the selectivities of neutral carrier ligands in electrode membranes

The selectivities of potassium and calcium ion-selective liquid membrane electrodes, based on neutral carrier ligands, have been studied in relation to the dielectric constant of the membrane solvent. Potentiometric measurements have shown that the selectivity for monovalent cations is favoured by a low dielectric constant, and that for divalent cations by a high dielectric constant of the solvent. This is in good agreement with theoretical predictions. The size of the calcium-selective ligand has also been estimated.