Expanded bed adsorption
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Expanded bed adsorption (EBA) is a preparative chromatographic technique which makes processing of viscous and particulate liquids possible. Where classical column chromatography uses a solid phase made by a packed bed, EBA uses a fluidized bed. Particles such as whole cells or cell debris, which would clog a packed bed column, readily pass through a fluidized bed. EBA can therefore be used on crude culture broths or slurries of broken cells, thereby bypassing initial clearing steps such as centrifugation and filtration, which is mandatory when packed beds are used. The feed flow rate is kept low enough that the solid packing remains stratified and does not fluidize completely. Hence EBA can be modeled as frontal adsorption in a packed bed, rather than as a well mixed continuous-flow adsorber.
The protein binding principles in EBA are the same as in classical column chromatography and the common ion-exchange, hydrophobic interaction and affinity chromatography ligands can be used. After the adsorption step is complete, the fluidized bed is washed to flush out any remaining particulates. Elution of the adsorbed proteins is commonly performed with the eluent flow in the reverse direction, that is, as a conventional packed bed, in order to recover the adsorbed solutes in a smaller volume of eluent.
EBA may be considered to combine both the "Removal of Insolubles" and the "Isolation" steps of the 4-step downstream processing heuristic.
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