Polishing

The purification steps after capture that remove remaining trace impurities and product variants: aggregates, host cell proteins, residual DNA, leached ligand and viruses. Typical steps are anion exchange in flow-through mode, cation exchange in bind-elute mode, hydrophobic interaction and mixed-mode chromatography, combined so that each uses a different separation principle. Japanese documents spell the loanword in two ways. The polishing train largely decides the final purity profile of the drug substance.