Tandem purification of proteins

A method of recovering a purified protein product from a load fluid, the method comprising:

• a) providing a first column comprising a first resin, wherein the first resin comprises protein A;
• b) providing a second column comprising a second resin, wherein the second resin comprises an anion exchange resin, wherein the first column is arranged in tandem with the second column;
• c) exposing the load fluid comprising a protein product to the first column under conditions in which the product binds to the first resin;
• d) recovering fluid comprising the product from the first resin to produce a first eluate;
• e) titrating the first eluate with a titrant continuously as it passes to the second resin, wherein the titrant comprises a pH buffer and at least 150 mM of a salt, and wherein the titrant is added at a target volumetric ratio to the first eluate such that there is a change in partition coefficient of less than 20% when the actual volumetric ratio of the first eluate to the titrant varies up to about 40% from the target volumetric ratio;
• f) exposing the titrated eluate to the second column under conditions in which the product binds to the second resin;
• and
• g) recovering fluid comprising the product from the second resin to produce a second eluate, thereby recovering the purified protein product from the load fluid.