Mobile Phases for Ion-Exchange Chromatography

Mobile phases, or eluents, in IEC are aqueous solutions of a salt or mixture of salts, often with a small percentage of an organic solvent added. The salt mixture may be a buffer, or a buffer may be added if required. The main component of the eluent is the competing ion that causes the solute ions to be eluted. 

In nonsuppressed IC, eluent competing ions of low limiting equivalent ionic conductance,47 such as carboxylate, are required. In suppressed IC, the mechanism of suppression dictates the choice of an eluent. In the case 

Chapter 2 Separations in High-Performance Liquid Chromatography 

Selectivity in the separation of ionic solutes may be varied by changing either the pH of the mobile phase or the nature or concentration of the displacing ions. The pH of the eluent affects not only the ionic form in which the eluent exists but also the form of the solute and the functional group on the ion-exchange resin. The nature and concentration of the displacing ion will determine the ease with which solute ions are displaced the more concentrated the competing ion in the eluent, the more effectively it will displace solute ions from the stationary phase. 

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