ABSTRACT
Most chromatographic separations utilize columns packed with beads. The bead diameter is an important factor: small beads result in fast diffusion times and large numbers of plates, but also high pressure drops. Large beads are used in process-scale separations to allow for increased flow rates without incurring high pressure drops and the resulting bed compression and eventual plugging. However, large beads have long diffusion times, low plate numbers, and low dynamic capacities. In 1988, membrane chromatography was first introduced as a means to overcome the limitations of column chromatography [1]. Microporous membranes containing immobilized ligands were used as the chromatographic media. Because the membranes were thin (∼0.1 mm), pressure drop limitations were not significant. Diffusional limitations were eliminated because solute was transported through the pores of the membrane by convection, not diffusion. The first devices were hollow fiber membranes where the surface was activated for affinity ligand attachment. Membrane chromatography has evolved since 1988. Several reviews of membrane chromatography spell out the evolution of the technology over the years [2-7]. Single-layer and hollow-fiber devices were abandoned because of poor performance. Affinity chromatography gave way to ion exchange chromatography as the primary ligand type. Vendor promotion turned away from protein purification to purification of large biomolecules such as plasmid DNA, viruses, and very large proteins (>250 kDa), where chromatography beads have low capacity. Applications such as viral clearance and purification of gene therapy vectors are examples. Three primary vendors have emerged for membrane chromatography products: Millipore Corporation (Bedford, MA, USA, Intercept™), Pall Biopharmaceuticals (East Hills, NY, USA, Mustang™), and Sartorius AG (Goettingen, Germany, Sartobind™). In this chapter, the principles and experimental methods applicable to membrane chromatography will be presented, and two applications will be offered as examples.
