Polishing Process Step
The final column in a production train is often referred to as the polishing step. At this point the feedstock contains a relatively high concentration of the target molecule with some select impurities or aggregates. The residual impurities however may be very closely related to the target and may be dimer, trimer, or isoforms of the target. In the case of synthetic peptides or oligonucleotides, "n-1", "n-2", etc. forms may remain. To separate these closely related molecules resins with high selectivity or efficiency are selected. Dynamic binding capacity remains important but buffer volume has been already significantly reduced.
For the polishing step, highly efficient smaller particle sizes of 35 µm and smaller are typically used. Also, more selective techniques such as hydrophobic interaction chromatography may be employed.
Many commercial TOYOPEARL and TSKgel PW bulk resin products are offered in particle sizes from 100 µm to 20 µm and have the same methacrylic polymer backbone. The selectivity of feedstock components on these resins remains the same regardless of bead size. TOYOPEARLresins with bead diameters of 35 µm and larger are made to withstand operating pressures up to 0.3 MPa. TSKgel PW resins with bead diameters of 20 and 30 µm are made to withstand operating pressures up to 2 MPa.