Intermediate Purification Process Step
The partially purified feedstock from the capture step will have a higher target concentration and relatively less complex impurity profile (also at higher concentrations). The intermediate purification step uses chromatography's resolving power to separate the target away from other impurities of the feedstock. Because of this, and the improved fluid flow properties, resin particle sizes of 65 µm and smaller are used. In many cases, more than one intermediate purification column may be necessary to achieve the desired degree of product purity.
The role of resin efficiency (particle size) and selectivity (ligand and pore size) become more important for intermediate purification. The question for the process chromatographer is "What percent of dynamic binding capacity can I load the resin to and still have adequate resolution from most impurities?"
Intermediate purification steps typically use smaller particles than capture steps. The viscosity of the intermediate feedstock and the operational pressure limits of the chromatographic hardware used, determine the most appropriate particle size for this process step.
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. TOYOPEARL® resins 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.