Separation Techniques

Membrane filtration (UF, NF, MF) is preferred for high-throughput bulk separation where selectivity requirements are moderate — typically 10–100× MW differences. Chromatography achieves higher purity (>99%) but at lower throughput and higher cost. For most biopharmaceutical processes, membranes handle initial capture/concentration while chromatography provides final polishing.

The general sequence is: (1) cell removal by centrifugation or microfiltration, (2) initial capture by affinity or ion exchange chromatography, (3) intermediate purification by size exclusion or additional chromatography, (4) formulation by UF/DF buffer exchange. This platform approach is used for mAbs, enzymes, and most recombinant proteins.

Small molecules (MW <1000 Da) are best separated by NF, crystallization, or reverse-phase chromatography. Proteins (MW >10 kDa) are best handled by UF, ion exchange, affinity, or size exclusion chromatography. The size gap is exploited most efficiently by matching MWCO to the target molecule MW — typically targeting 3–5× MWCO relative to the molecule of interest.