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Selectivity coefficients of a quaternary base ammonium anion-exchange resin toward a number of univalent anions have been measured. In some systems the selectivity coefficients varied little with composition, while in others a marked dependence was observed. Examples of the former included systems made up of various pairs of ions from Group A-halide, acetate, iodate and nitrate, or of pairs of ions from Group B-thiocyanate, perchlorate, di- and trichlolroacetate, trifluoroacetate, toluenesulfonate and naphthalenesulfonate. Examples of systems where the selectivity coefficient changed markedly were made up of an anion from Group A with one from Group B. These data were interpreted in terms of two postulated types of specific interactions (ion-pair formation) of these ions with those of the resin matrix. The ion-pairs of Group A were assumed to be randomly distributed in the resin phase, while those of Group B were assumed to occur in the form of “patches,” i.e., form clusters. The effect of temperature on the distribution coefficient was small; the concentration of the solution (when dilute) had a negligible effect upon the selectivity.
Gregor et al. (Sun,) studied this question.