Crown Ether Complexation in Electrical Double Layer of Anion-Exchange Resin

The complex formation of crown ethers with ammonium ions chemically bonded on the silica gel surface is affected by the nature of a counteranion and by the concentration of an anion in solution. Equations based on the Gouy−Chapman−Stern model for electrical double layers are derived to describe the adsorption isotherms of crown ethers and to elucidate effects of anion concentration on their chromatographic behaviors. Although the derived equations are not analytically solved, numerical solutions well describe experimental results. In the present case, the various types of interaction between the ammonium ion and counterions, i.e., the ion-pair (and triple ion) formation between the ammonium ion and a counteranion and the ion-pair formation between the ammonium ion complexed by a crown ether and a counteranion, are important and essential factors governing the overall adsorption of crown ethers. These constants are evaluated on the basis of the derived equation.