Method for obtaining unique selectivities in ion-exchange chromatography by addition of organic polymers to the mobile phase

We have observed that the addition of poly(ethylene glycol) (PEG) to the mobile phase systematically and significantly alters the retention behaviour of proteins in ion-exchange chromatography. The magnitude of the effect is proportional to the molecular mass and concentration of the added PEG. Retention of most proteins is increased, with fair correlation between protein size and degree of enhancement, but with significant influence by variations in protein surface chemistry. The charge on the exchanger and the native (nonenhanced) retention characteristics of the proteins appear to have no effect. Because of its independence from the native selectivity of the ion-exchanger, mobile phase polymer addition creates unique compound selectivites. Addition of PEG also increases viscosity, with the attendant affects of reducing flow-rate and dynamic binding capacity, while increasing eluted peak width.