Other Ion-Exchange Interactions

In addition to true ion exchange, other interactions can take place between the sample solutes and the resin. Adsorption is one of the commonest of these interactions. For example, the benzoate anion appears to be adsorbed somewhat by the poly-styrene-divinylbenzene polymeric matrix of organic ion exchangers. This may be due to an attraction of the k electrons of the aromatic polymer for the benzoate. Benzoic acid, which exists mostly in the molecular form, is absorbed to a much greater degree than benzoate salts. 

Much of the selectivity in separating mixtures of organic cations and anions has been shown to come from differences in adsorption rather than from differences in ion exchange selectivity [1,2]. However, adsorption and subsequent desorption is apt to be a slower process than ion exchange and is therefore to be avoided as much as possible in ion chromatography. 

Selectivity of Sulfonated Cation-exchange Resin for Metal Cations 

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