(a) passing a composition comprising the polypeptide of interest and various contaminants through an ion exchange membrane, wherein the polypeptide and membrane are shielded of charges by buffer ions and a pH sufficiently distinct from the pi of the polypeptide to enhance the charge of the polypeptide. Causing the membrane to bind to the polypeptide and at least one contaminant by having an opposite charge in operating conditions consisting of a buffer with a low ionic strength effective to prevent); (b) overloading the ion exchange membrane such that at least one contaminant remains and binds to the membrane while the polypeptide of interest is primarily present in the effluent; (c) collecting effluent from the ion exchange membrane comprising the polypeptide of interest; (d) subjecting the membrane effluent comprising the polypeptide of interest to a purification step of similar charge as the previous membrane, and (e) recovering the purified polypeptide from the effluent of the charged ion exchange chromatography purification step. Methods of enhancing the efficiency of downstream chromatography steps for purification of proteins are disclosed, comprising the step of: