How do you select and optimize chromatography resins for protein purification?

Resin selection considers: separation mode matching protein properties (pI for IEX, hydrophobicity for HIC, ligand availability for affinity), particle size (smaller for resolution, larger for flow rate and pressure), binding capacity (dynamic binding capacity at target residence time), and chemical/mechanical stability. Optimization involves: screening different resins at small scale, determining binding conditions (pH, conductivity), optimizing wash and elution conditions, measuring dynamic binding capacity vs residence time, and evaluating selectivity for impurities. Column qualification includes HETP/asymmetry testing. Scale-up maintains residence time while adjusting bed height and diameter. Resin lifetime studies determine reuse cycles.