Purifying antibodies by ion exchange chromatography.

Process for purifying an antibody from a composition comprising the antibody and a contaminant, wherein the contaminant is an acidic variant of the antibody, which method comprises the following steps performed sequentially: (a) binding the antibody to a cation exchange resin using a loading buffer, wherein the loading buffer is at a first conductivity and pH, wherein the amount of antibody loaded onto the cation exchange resin ranges from 20 mg to 35 mg of antibody per ml of resin exchange cationic; (B) washing the cation exchange resin with an intermediate buffer at a second conductivity and / or pH which is higher than the loading buffer to elute the contaminant from the ion exchange material; (C) washing the cation exchange resin with a wash buffer which is at a third conductivity and / or pH which is lower than the intermediate buffer; and (d) washing the cation exchange laresina with an elution buffer at a fourth conductivity and / or pH which is higher than the intermediate buffer to elute the antibody from the ion exchange resin.