In order to improve the production rates and lower the specific electrophoretic energy consumption values in preparative-scale, recirculating, binary isoelectric trapping separations, we propose to add an auxiliary isoelectric agent to the solution in the anodic separation compartment and another to the solution in the cathodic separation compartment to implement pH-biased isoelectric trapping. The auxiliary isoelectric agents are selected such that they are trapped in the respective anodic and cathodic separation compartments and also, have isoelectric point (pl) values that are different from the pl values of the analytes of interest. By proper selection of the auxiliary isoelectric agents and their concentrations, the analytes of interest can be kept in nonisoelectric, charged state during the entire course of the preparative-scale, recirculating, binary isoelectric trapping separation. This results in higher electrophoretic mobilities and solubilities for the analytes than in their isoelectric or near-isoelectric states, and leads to faster binary isoelectric trapping separations.