Principles of Ion-Exchange Chromatography

The general problem in all chromatographic separations is the selection of conditions such that the distribution ratios of the solutes to be separated differ as widely as possible. With chromatographic columns of practical dimensions, having up to 500 equivalent theoretical plates, differences in distribution ratio of at least 10% are desirable for adequate separations (12). In addition, the maximum amount of solute retained by the resin stationary phase should not exceed about 2% of the maximum exchange capacity, in order to obtain linear exchange isotherms. This precaution also ensures the maximum rate of solute exchange for a particular solute-resin system. 

The first method is most widely used. In cases where solubility data exist for the relative affinities of the displacing ion and the solute in question, it is possible to formulate exact relationships between the solute distribution ratio and the concentration of the eluting ion in the mobile phase. 

The second method of varying the distribution ratios by changing the degree of ionization of the fixed groups in the resin is a special case of the first method. The method is not very suitable for strongly basic anion-exchange resins, such as those customarily employed in the work with bile acids. 

The pH value, however, is that of the surface of the resin. This will differ from that in the bulk of the external solution on account of the surface charge on the resin (26). In case of the bile acids, the pK values should also be those of the surface of these molecules. 

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Ion Exchange Chromatography - Basic principles of ion exchange chromatography and studies conducted from Texas A M University. http //ntri.tamuk.edu/fplc/ion.html. 

Figure 6.11 Principle of ion-exchange chromatography, in this case anion exchange chromatography. The chromatographic beads exhibit an overall positive charge. Proteins displaying a nett negative charge at the pH selected for the chromatography will bind to the beads due to electrostatic interactions...

FIGURE 6.4 Schematic illustration of the principle of ion exchange chromatography. 

Illustration of the principles of ion-exchange chromatography. See text for explanation. 

A rigorous mathematical treatment of ion-exchange chromatography would be rather complex and well beyond the scope of this text. A brief description of the principles of ion-exchange chromatography is given below. 

The principles of ion-exchange chromatography are discussed in ch. 3. Here, some useful elution systems for nucleotides are described. The descriptions are based on published work and the author s experience but it must be emphasised that variations between batches of Dowex resins may make the methods difficult to repeat and any method should be rigorously tested before use (e.g. Matthews 1968a). 

The principle of ion-exchange chromatography is not unlike that of adsorption chromatography. In the latter case, the adsorbent bears active sites which interact with molecules in their vicinity to a more or less specifically defined extent. Sample and solvent molecules compete with each other for adsorption. 

The principles of ion-exchange chromatography are well described and may be represented by the equation... 

Fig. 2.7. Principle of ion exchange chromatography. Negatively charged sample components are adsorbed on the stationary phase and thus separated from positively charged and uncharged sample components. The adsorbed components are then eluted by increasing the ionic strength of the mobile phase.

The principle of ion-exchange chromatography is as follows Ions differing in their charges interact with the functional groups of the exchanger with different intensities, and can be selectively eluted from the matrix by changing the elution... 

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