Protein purification using ion exchange chromatography.

A method for purifying a polypeptide from a composition comprising the polypeptide and a contaminant, said method comprising the following steps performed sequentially: a) binding the polypeptide to an ion exchange material using a loading buffer, wherein the loading buffer is at a first conductivity and pH; b) washing the ion exchange material with an intermediate buffer at a second conductivity and / or pH so as to elute the contaminant from the ion exchange material; c) washing the ion exchange material with a wash buffer which is at a third conductivity and / or pH, wherein the change in conductivity and / or pH of the intermediate to the wash buffer buffer is in an opposite direction to the change in conductivity and / or pH of the loading buffer to the intermediate buffer; d) washing the ion exchange material with an elution buffer at a fourth conductivity and / or pH so as to elute the polypeptide from the ion exchange material.