Acta Chimica 87. (1975)
3. szám - ANALYTICAL CHEMISTRY - Marton Aurél–Halmos P.–Inczédy J.: Resin-Phase Concentration Dependence of Anion-Exchange Equilibria
Acta Chimica Academiae Scientiarum Hungaricae, Tomus 87 (3), pp. 205 — 213 (1975) RESIN-PHASE CONCENTRATION DEPENDENCE OF ANION-EXCHANGE EQUILIBRIA A. Marton, P. Halmos and J. Inczédy (Research Group for Analytical Chemistry of the Hungarian Academy of Sciences Veszprém) Received March 6, 1975 An equilibrium-column technique has been applied to evaluate the dependence of anion-exchange equilibrium constants for monovalent and bivalent organic acid anions on the resin-phase composition. Ion-exchange isotherms for monovalent and bivalent anions of maleic and fumaric acids were obtained, at various total normalities. The corrected selectivity coefficients show a remarkable change with the resin-phase concentration in all cases. Selectivity reversal was observed at higher resin loading in all cases, indicating a remarkable difference between the states of the resin hydration in the two different ionic forms. Dowex AG 1X4 (100 — 200 mesh) chloride form anion-exchange resin was used. All data were obtained for systems at 25°C, in aqueous media. Introduction For a quantitative definition of the selectivity of ion-exchange reactions the selectivity coefficient is generally used.* A number of experimental evidences prove, however, that the selectivity coefficient is not a true constant hut for a given system and temperature it is a function of the ionic composition of the exchanger phase [1]. In the field of cation exchange a considerable number of measurements were published on the dependence of selectivity coefficient on the resin-phase concentration. The purpose of these studies was to obtain the thermodynamic equilibrium constant, and a selectivity scale thermodynamically established. Selectivity scales based on the equilibrium constants were presented for the equilibria of a number of monovalent [2] and bivalent [3] cation pairs, of which only a few examples are being mentioned here. Much less information is available for analogous investigations on anionexchange equilibria. Early works of Wheaton and Bauman [4] and Peterson [5] and later Gürtler and Santana [6] present some values for anion-exchange equilibria, however, they are not true thermodynamic data but rather selectivity coefficients which are given together with the degree of transformation of the resin under equilibrium conditions. *Apart from selectivity coefficients distribution coefficients are also widely used for comparing the selectivity of ions for resins. Their use is advantageous in chromatography where the distributing species is only a trace component. Acta Chim. (Budapest) 87, 1975