ELECTROCHEMICAL PROPERTIES OF CELLULOSIC ION-EXCHANGE MEMBRANES .3. APPLICATION TO ION-SELECTIVE ELECTRODES

The electromotive force of the galvanic cell SCE/satd KCl/solution (2) /cationic membrane/solution (1)/anionic membrane/solution (2)/satd KCl /SCE has been measured for various electrolytes, using cellulosic cati on- and anion-exchange membranes which behave as ideal or nearly ideal reversible electrodes. This method affords a simple means of determin ing the mean activities of numerous salts, including many for which ot her electrometric methods are not available, without the need to make extra-thermodynamic assumptions. The agreement between the values of t he activities found and those tabulated in the literature is excellent in the range of concentrations studied less than or equal to 0.1 mol/ kg, even for salts containing di- and tri-valent ions. This method is also suitable for measuring the mean activity of salts in solutions of polyelectrolytes as we report for the variation of 0.1 KCI activity w ith different amounts of the protein beta-lactoglobulin. The main reas on for the high performance of this system as a reversible electrode f or a variety of salts, lies in the fortunate mutual compensation of th e water transport effect for the two cellulosic membranes, together wi th a negligible effect on the cell emf of the liquid film adhering to the membranes, circumstances which have been thoroughly discussed. The measurements were carried out at 25 +/- 0.05 degrees C.