Weak partitioning mode of operation enhances the F/T mode by identifying solution conditions wehre there is weak binding of MAb to the resin (2 to 20 g/L). Under these conditions the impurities bind stronger than in the F/T mode and thus enhanced purificaiton is obtained. However, load conditions are targeted to have a low product partition coefficient (Kp) in the range of 0.1-20. (Nadarajah, US 14/355,818)

Kelley ( US8,067,182, US2007/0060741A1, equivalent foreign filing is Brown (WO 2006/099308); see also “Weak Partitioning Chromatography for Anion Exchange purification of Monclonal Antibodies” Biotechnology and Bioengineering 101(3): 553-566 (2008) describes a third mode for the operation of chromatography columns referred to as a “weak partitioning mode” where at least one product and at least one contaminant both bind to the chromatographic resin. However, the impurities bind more tightly to the medium than the product and loading continues, unbound product passes through the medium and is recovered from the column effluent. The medium is optionally subsequently washed under isocratic conditions to recover additional weakly bound product from the medium and the purified product is pooled with the product from the column effluent. The more stringent load conditions under a weak partitioning mode are disclosed to result in much stronger impurity binding, which improves the product pool purity. Weak partioning mode may be used in conjuction with any chromatographic resin or medium for separation of a product form impurities. Emobdiments include ion exchange resins, HIC resins, hydroxyapatite chromatography, immobilized metal affinity chromatography. Before loading, it may be necessary to identify the region of weak partitioning by finding the operating conditions which cause the meidum to bind at least 1 mg of product per mL of medium. 

As applied to specific Resins

AEX:

Weak paritioning AEX chromatography requires a precisely formulated mobile phase to accomplish retention of stronger binding impurities, such as HMW species and HCP at the expense of a weaker binding product. The binding strenght is determined by a thermodynamic partition coefficient, Kp, which is calcualted form batch binding experiments as the ratio of absorbed protein concentration to free protein cocnetrations at equilbirum. Kp is a function of pH and concentration of anions (typically, Cl- in the AEX equilibration loading and wash buffers. The Kp=f(pH, [Cl-]) function is empirically dervied from batch binding experiments. Coffman (US13/811178)

ProA–AEX: In traditional batch chromatography mode, a pro A peak is eluted with a low-pH buffer, containign glycine as a buffering agent and salt (NaCL) which is a major source of chloride ions that control the binding strenght to AEX downstream The pooled peak is titrated with a concentrated neutralizing agent (high pH Tris buffer) until the desired pH is reached. Thus, Kp of the AEX load is controleld by accurate formulation and titration of the proA elution buffer. Coffman (US13/811178) teaches a tandem arrangement of ProA-AEX where pumps are synchronized to deliver a pre-programmed variable ratio of buffers. The first eluate produced from the ProA is continuously titrated with a pH buffer and at least 150 mM of a salt and the titrant is added at a target volumetric ratio such that there is a change in partition coefficient of less than 205 when the actual volumetric ratio of the first eluate to the titrant varies up to about 40% from the target volumetric ratio.