Preparative elution chromatography is generally carried out under mass and/or volume overloaded conditions in order to increase the product throughput. In volume overloading, the sample concentration is maintained in the linear region of the isotherm and the volume is increased until the throughput is optimized. A fundamental problem with this technique is the under-utilization of the column and the corresponding low throughputs. In mass overloading, the sample concentration is increased beyond the linear adsorption region, resulting in asymmetric band profiles, with self-sharpening fronts and tailing rear boundaries for Langmuirian adsorption systems. A combination of volume and mass overloading is commonly used to maximize throughput in preparative elution chromatography.
In recent years displacement chromatography has received considerable
attention as a promising preparative chromatographic technique for protein
separations. The key operational feature which distinguishes displacement
from step elution chromatography is the use of the displacer compound.
The displacer is selected such that it has a higher affinity for the stationary
phase than any of the feed components. A large volume of the feed
mixture is then loaded onto the column, followed by a constant front of
the displacer solution. The displacement process is based on the
competition of solutes for adsorption sites on the stationary phase according
to their relative binding affinities and mobile phase concentrations.
The action of the displacer causes the feed components to migrate through
the column at velocities greater than that dictated solely by their individual
adsorption isotherms. The product components exit from the column
as adjacent "square wave" zones of higher concentrated pure material, in
the order of increasing affinity of adsorption.