An Isotachophoretic Model of Counteracting Chromatographic Electrophoresis (CACE)

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Abstract
Counteracting chromatographic electrophoresis (CACE) is a new electrophoretic technique for preparative separation of charged macromolecules, particularly proteins. CACE combines gel chromatography of a protein sample in a packed bed of gel beads having a gradient of exclusion limit, simultaneously with electrophoresis in an electric field tending to move the protein upstream. The target protein's convective movement opposes its electrophoretic movement, focusing the protein into an accumulation zone where its net velocity is zero. A mathematical model of concentrations and electrical fields in CACE was derived from an analogy to isotachophoresis. Accumulation-zone concentrations, electrical field, and pH were calculated from the bulk flow and electrophoretic fluxes of the target protein and buffer constituents, along with expressions for charge conservation and electroneutrality. The model predicts conditions for formation of protein accumulation zones given column operating parameters and mobility data for the target protein. Operating conditions correspond with available data on the CACE process, but calculated protein concentration was lower than that found experimentally.