Abstract: A wash buffer comprising greater than 0 mM and less than about 500 mM arginine, greater than 0 mM and less than about 250 mM guanidine, greater than 0 mM and less than about 250 mM sodium chloride, and greater than 0 mM and less than about 50 mM of an anionic surfactant, or greater than 0% and less than about 0.25% w/v of a non-ionic surfactant. When used during affinity chromatography purification of a protein of interest, such as an antibody, the wash buffer significantly reduces the level of host cell proteins from the preparation. Following affinity chromatography with the wash buffer, the protein of interest may be further purified using membrane chromatography.