High Performance tangential flow filtration (HPTFF): is where the protein separations are carried out on the basis of both size and charge (US 2003/0229212). HPTFF is thus a two-dimensional purification method which can separate biomolecules with the same molecular weight. It is even possible to retain one biomolecule while passing a larger molecular weight species through the membrane. The degree of polarization increases with increasing concentration of retained solute in the feed, and can lead to a number of seemingly anomalous or unpredictable effects in real systems. For example, under highly polarized condtions, filtration rates may increase only slightly with increasing pressure, in contrast to unpolarized conditions, where filtration rates are usually linear with pressure. Use of a more open, higher flux membrane may not increase the filtration rate, because the polarized layer is providing the limiting resistance to filtration. The situation is further complicated by interactions between retained and eluted solutes. (WO 2005/091801).

HPTFF exploits a number of different stategies to achieve high resolution separations including (1) proper choice of pH and ionic strenght to maximize differences in the hydrodynamic volume of the product and impurity, (2) use of electrically charged membranes to enhance the rentation of like charge protines (3) operation in the pressure dependent regime to maximize the selectivity and (4) use of a diafiltration mode to wash impurities through the membrane (Cheang, J. Membrane Science 231 (2004) 159-167)

Parameters

The success of HPTFF is based on several important factors such as operating pressure, flux and selectivity (Szena “Advances in Colloid and Interface Science 145, 2009 1-22. 

Knowledge of the isoelectric point (pI) of the desired molecule of interest is the main factor in HPTFF. This will then dictate membrane setup and the intrinsic charge profile of the membrane, pore size and flow characteristics. For example, Perrault (WO 2005/091801) discloses that the isoelectric point of human alphafetoprotein is about 5 and the pI of the membrane is 7. In order to maximize the retention of human alphafetoprotein, the pH of the buffer solution was chosesn to be between 6-6.5. Under these conditions, both the membrane and recombinant alphafetoprotein will have a negative charge and repel each other.