Examining the effect of protein size on transport and adsorption in polymer-modified ion- exchange media

Ion-exchange particles in which functionalized secondary polymers have been grafted onto the base matrix have been shown to offer significant performance advantages over traditional particles, especially with respect to increases in dynamic binding capacity (DBC). However, the mechanistic origins of these advantages are not clearly understood. A number of studies have found that, depending on pH and flow rate, a maximum in the DBC can exist as a function of ionic strength, suggesting that the key lies in the balance between improved transport at higher ionic strengths and improved static capacity at lower ionic strengths. The broad goal of this work is to gain a better understanding of this interplay between protein transport and adsorption that accounts for observed column breakthrough performance in both traditional and polymermodified particles. To this end, the model proteins lysozyme, lactoferrin, and a monoclonal antibody (mAb) are used to examine the role of protein size in column breakthrough performance on the traditional resin SP Sepharose FF and on the dextran-modified resins SP Sepharose XL and Capto S, each having an agarose base matrix. The base matrices for FF and XL are similar, providing an especially good basis for examining the role of the dextran.