Purification is the downstream processing stage in which a target biological molecule — such as a recombinant protein, viral vector, plasmid DNA, or mRNA — is isolated and refined from a complex harvest material by removing process-related impurities (e.g., host cell proteins, host cell DNA, residual reagents) and product-related impurities (e.g., aggregates, truncated forms). It typically involves a series of unit operations — including chromatography, filtration, viral inactivation, and ultrafiltration/diafiltration (UF/DF) — designed to achieve the required purity, potency, and critical quality attributes (CQAs) in a scalable and GMP-compliant manner.
