The electrochemical properties of the membranes were studied in sodium acetate solutions as functions of qualitative and quantitative membrane composition. Compositions were revealed which will guarantee the widest range of functioning. The selectivity of the membranes for acetate ions was studied in the presence of a number of foreign anions as a function of membrane composition. A model is discussed which can be used to establish the connection between membrane selectivity and solvation of the ions in the membrane phase. The possible stoichiometry of the compounds formed between anions and ligands is inferred from this model and from the results obtained.