Ultrafiltration/Diafiltration (UF/DF) is a membrane-based separation technique used in downstream processing to simultaneously concentrate a biological product and exchange its surrounding buffer or solvent by passing the process stream through a semi-permeable membrane that retains molecules above a defined molecular weight cutoff (MWCO) while allowing smaller molecules — such as salts, impurities, and process reagents — to pass through. Ultrafiltration achieves product concentration, while diafiltration enables buffer exchange and impurity removal by continuously adding fresh formulation buffer. UF/DF is a critical unit operation in the purification and formulation of recombinant proteins, monoclonal antibodies (mAbs), viral vectors, and plasmid DNA (pDNA), and must be optimized and validated as part of the downstream process development workflow.
