Protein Adsorption in Tentacle-Type Anion Exchangers and the Influence of Process Related Fouling

The physical and protein adsorption properties of Fractogel TMAE, a tentacle-type anion exchange resin, were investigated for both virgin and used samples to determine the influence of process related fouling. The resin average particle diameter was found to vary between 70 and 72 μm for different resin lots. Inverse size exclusion chromatography (iSEC) indicated a bimodal distribution of pore sizes, with some large pores, 40 nm in radius. occupying about 9% of the particle volume and much smaller pores, with radius between 4 and 5 nm, occupying 74% of the particle volume. Similar results were obtained by iSEC for resin samples fouled by process use, indicating that the core structure of these particles is unchanged. Transmission electron micrographs (TEM) showed that the resin backbone has a microgranular structure and that the same structure persists. In this case, however, a dense layer, approximately 0.5 μm thick, was also seen at the particle exterior surface of the fouled particles. The equilibrium binding capacity of BSA was determined to be 178±1 mg/mL for both virgin and fouled samples, respectively, while the corresponding values for Thyroglobulin were 95±4 and 25±2 mg/mL. The BSA adsorption kinetics was also 2-3 fold slower for the fouled resin, but much larger differences between virgin and fouled resin were seen for the much larger Thyroglobulin. Based on the shape of intraparticle protein concentration profiles determined by confocal laser scanning microscopy (CLSM), the protein transport mechanism was determined to be “solid diffusion” for both virgin and fouled resin samples and proteins. However, transport of Thyroglobulin was much slower for the fouled sample as a result of its larger size and increased diffusional hindrance in the fouled surface layer. The key conclusion is that fouling occurs through the formation of a think but very dense skin layer that greatly affects the transport kinetics of large proteins.