Retention model for high-performance ion-exchange chromatography

Protein retention on an ionic surface is the result of protein charge, surface charge and the charge characteristics of the surrounding medium. To date, a “net charge” model has been used to explain this phenomenon; however, retention mapping studies on strong ion-exchange columns showed it to be inadequate. Deviations may result from charge asymmetry, since it appears that only a fraction of the protein surface interacts with the stationary phase. Retention is also altered by the type of displacing salt. A non-mechanistic model has been developed which shows a positive correlation between protein retention and the number of charges associated with the adsorption-desorption process. Integration of these observations and concepts provides a deeper understanding of protein retention on ion-exchange surfaces.