Principle involved in ion-exclusion method:

For understanding the principle of ion exclusion, we will have to visualize that a column of ion exchange contains three phases; the solid network of resin beads, the liquid inside the bead ( resin liquid) and the liquid surrounding the bead (interstitial liquid). Most low molecular weight solutes diffuse in and out of the liquid phase inside the bead (resin liquid). However, the organic nonionic solutes tend to exist at the same concentration in both the resin liquid and interstitial liquid phases. The ionic materials, because of Donnan membrane effect, exist at a considerably lower concentration in the resin liquid than in the interstitial liquid phase. Therefore a solution containing an ionic and nonionic component is placed on the top of column and washed with water the ionic material will reach the bottom first followed by elution of nonionic component.