The Mechanism of Chromatographic Retention - Chromatographic Interactions > Ionic Interactions > Page 15

With the exception of the ion exchange properties of the stationary phase both columns are identical. The separation was developed on both columns by a linear gradient from pure water to 0.5M NaCl in 0.2M phosphate at pH 7.0 over a period of 60 minutes. The chromatograms shown in figure 6 show some interesting differences. The different order of retention that is obtained does not simply reflect the ion exchange character of the resin. Polar and dispersive forces accompany the ionic interactions and the net effect of changing the ion exchange material is not straightforward. The strong ion exchanger was TSKgelSP-5PW the weak ion exchanger TSKgelCM-5PW. The properties of the phases are included in the diagram

The terms dispersive, polar and ionic are used to describe specific types of interaction and if a substance provides predominantly one type of interaction, then the same terms can be employed. For example, a hydrocarbon molecule that offers exclusively dispersive interactions to other molecules could be described as a dispersive substance. However, complex molecules, particularly in the biotechnology field, have many different dispersive, polar and ionic groups in their total structure and thus the overall interactive character may be largely ionic, dispersive or polar depending on the distribution of the different interactive groups. It follows, that terms are required to describe the overall interactive property of a molecule as opposed to the interactive character of its specific groups.

Virtually, by default, the most common terms that have been established to describe molecular interactive character are hydrophobic and hydrophilic. A hydrophobic substance is predominantly dispersive in character and a hydrophilic substance is predominantly polar in character. Two other terms are less commonly used for the same purpose and they are lyophobic and lyophilic which are synonymous to hydrophobic and hydrophilic. The terms have a rather obscure origin and are not based on physical chemical considerations, but have evolved, somewhat arbitrarily, from the discipline of biology. Nevertheless, they are of great significance to biologistsandbiochemists