Analytical Sciences

Abstract − Analytical Sciences, 24(9), 1123 (2008).

Ion Exchange and Protonation Equilibria of an Amphoteric Ion-exchange Resin in the Presence of Simple Salt
Yoshinobu MIYAZAKI, Hui QU, and Junko KONAKA
Department of Chemistry, Fukuoka University of Education, Akamabunkyo-machi, Munakata, Fukuoka 811-4192, Japan
The influence of simple salts on the ion exchange and protonation equilibria of an amphoteric ion-exchange resin, which has strong base and weak acid moieties in a single functional group fixed onto the styrene-DVB matrix, has been investigated. Concentrations of ionic species in the amphoteric ion-exchange resin in equilibrium with various sodium salt solutions were estimated by 23Na NMR spectroscopy. For the NaClO4 system, the ratio of sodium ion concentration in the resin phase to that in the equilibrium solution was greater than 1 and increased with a decrease in the salt concentration. In contrast to an ordinary cation-exchange resin, the ion exchange behavior of Mg2+ and Ca2+ on the amphoteric ion-exchange resin showed a marked dependence on the kinds of salts: the distribution coefficients for the NaCl system were independent of the salt concentration, while the log D vs. log[Na+] plots for the NaClO4 system showed linear relationships with slopes being neither -2 nor 0. Apparent protonation constants of the carboxylate in the functional group of the resin in equilibrium with NaClO4 solutions were greater than those with NaCl solutions. The ion exchange and protonation properties of the amphoteric ion-exchange resin were elucidated on the basis of the information about the salt concentrations in the resin phase estimated by the NMR method.