CHARACTERIZATION AND APPLICATIONS OF CHELATING RESINS AS CHEMICAL REAGENTS FOR METAL-IONS, BASED ON THE GIBBS-DONNAN MODEL

The Gibbs-Donnan model for ion-exchange resins is used to describe and predict the sorption equilibria of metal ions on chelating resins. Th ese are characterized by their intrinsic complexation constants, which , according to the model, are related to the complexation constants in solution with Ligands having structure similar to that of the active groups in the resin. The intrinsic complexation constants are independ ent of the experimental conditions, for instance the composition of th e solution phase. The model is applied to two different kind of chelat ing resins: a strong anion exchanger loaded with sulfonated azo dyes, and a weak cation exchanger with iminodiacetic groups (Chelex 100) cov alently linked to the mainframe. In most cases the complexation inside the resin exactly corresponds to that in aqueous solution, while some times the formation of 1-to-2 complexes is promoted inside the resin. In any case the intrinsic complexation constants allow us to evaluate the exchange coefficients, holding at the particular conditions, by th e Gibbs-Doman model. Thus the sorption and elution of a metal ion by a batch procedure can be predicted. A particular application is describ ed, which is useful in the field of analytical chemistry. It is the de termination of total and free metal-ion concentration in an aqueous so lution of unknown composition, at very low concentration of metal. Thi s also is made possible by the knowledge of the exchange coefficients at the particular conditions. (C) 1998 Elsevier Science B.V. All right s reserved.