With different mediator solvents, such as di(n-octyl) phenylphosphonate, tri-Bu phosphate, nitrobenzene, o-nitrophenyl n-octyl ether, dioctyl phthalate, and di-Bu sebacate, selectivities of PVC membranes for alkali metal ions were measured. The factors affecting selectivities of sensitive membranes were investigated by measuring equilibrium conductances of tetraphenylborates in different mediator solvents. The conclusions obtained agreed with experimental results. As a mediator solvent nitroaroms. are suitable for alkali metal ions with larger radii, and phosphonates are favorable for alkali metal ions with smaller radii.

Key words: TETRAPHENYLBORON-SODIUM, PHENOL P, PHENOL ETHER, ALKALI METAL, PHOSPHORIC ACID TRIBUTYL ESTER, ION SELECTIVE ELECTRODE, POLYVINYL CHLORIDE, PHOSPHONIC ACID ESTER, SELECTIVITY, MEMBRANE ELECTRODES