Stationary phase in ion-exchange chromatography

In ion-exchange chromatography (lEC), the mobile phase modulator is typically a salt in aqueous solution, and the stationary phase is an ion-exchanger. For ddnte conditions, the solute retention faclor is commonly found to be a power-law function of the salt uormahty [cf. Eq. (16-27) for ion-exchange equilibrium]. 

Note 3 Macroporous polymers are used, for example, as precursors for ion-exchange polymers, as adsorbents, as supports for catalysts or reagents, and as stationary phases in size-exclusion chromatography columns. 

Figure 4.2—Stationary phases in ion chromatography. Schematic of a polystyrene sphere used as a cation exchanger. The polystyrene matrix is transformed into a resin that can exchange cations (e.g. DOWEX 4) or into an anion exchange resin (e.g. DOWEX - MSA-l, or Permutite" if R = CH,).

Ion Exchange Chromatography. In ion exchange chromatography (IEC), the solid stationary phase is comprised of ionic material. This serves as an ion exchanger and separation is achieved primarily on the basis of the relative affinities of... 

A strategy for the selection of the stationary phase is developed based on a discussion of the mechanism underlying the separation involved in gel filtration, reverse-phased, and ion-exchange chromatography. 

Ion-interaction chromatography is an intermediate between reversed-phase and ion-exchange chromatography. Introduction of amphiphilic and Uo-philic ions into the mobile phase causes their adsorption on the hydrophobic surface of packing material with subsequent transformation into a pseudo ion-exchange surface. Ionic interactions with charged analytes can occur in the mobile phase and with counterions that may be adsorbed on the stationary-phase surface. 

Retention volume Change in temperature can affect the distribution of a sample between the mobile and stationary phases and thereby affect retention behavior. In ion-exchange chromatography the effect of temperature is slight, but when the value of the partition ratio depends on adsorption, temperature variation is more significant. In gas-liquid chromatography the effects of temperature have been thoroughly studied, and the fundamental retention relation is... 

Since electrical neutrality must be maintained in ion-exchange chromatography, the distribution of ions between the mobile and stationary phases is complicated by the need for counterions. The use of partition or distribution ratios in the usual way is therefore not entirely appropriate instead, a selectivity coefficient is used to denote the equilibrium distribution of ions. Thus for (25-1) and (25-2) the law of mass action... 

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