Purification of bioproducts by free-flow zone electrophoresis: choice of processing parameters

Free-flow zone electrophoresis may be used to purify biological samples, due to differences in electrophoretic mobility, in absence of a matrix--most frequently a gel--thus enabling the biological integrity of even fragile molecules to be preserved. However, the process is more complicated than its principle suggests due to different transport phenomena interfering with electrophoretic migration, with the resultant separation depending both on separation effects and dispersive phenomena. The physical origin of the main effects involved was identified. Mathematical expressions were proposed to estimate the influence of the crescent effect and electrohydrodynamics on the process. In this paper, these equations are used to determine the minimum difference in electrophoretic mobility required for a separation to be achieved with respect to the processing parameters. A methodology is proposed which defines the conditions under which the difference in electrophoretic mobilities equals that calculated when considering the influence of dispersive phenomena. Optimized separations of the whey proteins lactoferrin and albumin, known to interact strongly, and the purification of a monoclonal antibody from a mouse ascitic fluid illustrate the approach.