Ion Exclusion Chromatography: Model Development and Experimental Evaluation

Ion exclusion chromatography (IEC) is a separation technique used both at analytical scale for the simultaneous determination of ionic species and at preparative scale for the separation of strong electrolytes from weak electrolytes and nonelectrolytes. In this work, a column model for IEC is developed and evaluated by comparison with experimental data. The model explicitly takes into account the Donnan equilibria responsible for the exclusion of electrolytes from the resin pores. At the high electrolytes concentrations typical of preparative scale separations, resin shrinking becomes an important factor, affecting the variation of inter- and intraparticle void fractions. The effect of the electrolytes concentration on resin shrinking has been experimentally studied, and the volumes variation was included in the model equations. At the analytical scale, the proposed model is able to predict the effect of electrolytes concentration on the extent of exclusion from the resin pores and the influence of the degree of dissociation of weak electrolytes on their retention time. At preparative conditions, discrepancies between the experimental data and simulations results are observed for divalent salts. Since such discrepancies arise at the largest concentrations, they have been imputed to the main model assumption of ideal thermodynamics.