Axial Flow

Figure 4. Conventional chromatography columns operate in axial flow in which the mobile phase moves along the axis of the column. In radial flow, the mobile phase is applied to the surface of the column and moves along its radius to the centre.

Another new approach to protein separations is expanded bed chromatography which was recently developed by Pharmacia (Patent No. W09218237, 1992). This utilizes 200 pm agarose beads with quartz cores to increase their density. The flow of liquid into the bottom of the column causes the bed to expand under hydrodynamic pressure. On the introduction of the feedstock, the space between the beads in the expanded bed allows debris and insoluble material to pass through the column while proteins in solution bind to the ion-exchange medium. To recover the adsorbed material, the flow is reversed and proteins are eluted from the bottom of the unexpanded bed, as in conventional chromatography. The advantage of this system is that feedstocks may be applied directly from a fermenter stream, without prior

Figure 4. Conventional chromatography columns operate in axial flow in which the mobile phase moves along the axis of the column. In radial flow, the mobile phase is applied to the surface of the column and moves along its radius to the centre.

clarification by centrifugation or filtration (Hjorth et al, 1993). Pharmacia have claimed 40% cost savings using this method for the purification of a bacterial protein from 8000 1 of periplasmic lysate (reported by McCormick, 1993).

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