Complexation of Polyethers in Cation Exchange Resin and Application to Chromatographic Determination of Complexation Constants in Solution

Abstract

The complex formation of crown ethers with counterions in cation-exchange resin is chromatographically evaluated with a model based on the Poisson−Boltzmann−Gouy−Chapman−Stern theory. In the model, two contributions are taken into account to explain distribution ratios (or chromatographic capacity factors) of crown ethers; one is the ion-pair formation of a cation−crown ether complex with a sulfonate group chemically bonded on silica gel, and the other is the accumulation of cationic complexes in the diffuse layer. To describe this system, at least three equilibrium constants are necessary; a complex formation constant and two ion-pair formation constants between a cation-exchange site and a countercation and between a cation-exchange site and a cation complexed by a crown ether. The combination of two chromatographic methods, i.e. the crown ether retention and the retention of a probe cation under effects of the crown ether complexation with eluent cations, allows quantitative evaluation of equilibrium constants necessary for numerical calculation. Thus, crown ethers can probe the equilibria not evaluated by other approaches. The results of the calculation are used for the evaluation of the validity of a simple equation previously reported for the chromatographic determination of the complex formation constants of polyethers in solution.