Capture Process Step
A chromatographic "capture" or "concentration" step is a column just downstream of the harvested feedstock after initial clarification. Its primary function is to "capture" the target from solution and separate it from the most dominant impurities. The target is then eluted into a significantly smaller volume of buffer for further downstream processing. A resin is selected which has the best combination of dynamic binding capacity, mass recovery, and retention of the target's biological activity.
Column dimensions and resin particle sizes tend to be larger in capture steps. The feedstock viscosity, the amount of particulate, and the operational pressure limits of the chromatographic hardware used, determine the most appropriate particle size for a capture step. The more viscous and particulate laden the feedstock, the larger the particle needed to produce a linear velocity suitable for the process throughput objectives.
The typical capture step for monoclonal antibodies (mAbs) is based on Protein A affinity chromatography. This affinity step provides a high selectivity and yields a high purity of the target molecule in one step. By applying latest resin technology the dynamic binding capacity could be raised to more than 70 g IgG or mAb per liter Protein A resin. As raw treated feedstocks have become more clarified and less viscous, there is a trend to use smaller particle materials for capturing.
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.