The potentiometry with alkali metal ion-response glass electrode has been used to obtain the standard molar free energies of transfer, DGt? of alkali metal chlorides from water to tri-Bu phosphate (TBP)-methanol mixtures at 25癈. The relationship between ion solvation and selectivity of PVC membranes for alkali metal ions has also been studied. As increase of contents of TBP in mixtures, DGt?of alkali metal ions increases, and DGt?rises also with increase of ion radii. This case is in agreement with sequence of selectivity of TBP-PVC membrane for alkali metal ions, but it is not in accord with sequence of selectivity of TBP-PVC membrane based on tetraphenylborate. The results shows that the selectivity of PVC membrane electrodes based on tetraphenylborate is affected by reaction constant of ion exchange between aqueous solution and membrane as well as other factors, besides ion solvation.

Key words: PHOSPHORIC ACID TRIBUTYL ESTER, ION SELECTIVE ELECTRODE, SELECTIVITY, MEMBRANE ELECTRODES, PHASE TRANSFORMATION, WATER PHASE, POLYMER FILMS, CORELATIONS, METAL ION, ALKALI METAL ION