Protein-solute interactions affect the outcome of ultrafiltration/diafiltration operations.

Protein production operations often involve a final diafiltration of the protein into formulation buffer. For several Amgen product proteins, post-diafiltration assays revealed a significant difference in molar excipient concentrations on the retentate and the permeate side of the membrane. For example, post-diafiltration assays of formulated 200 mg/mL human interleukin-1 receptor antagonist showed molar chloride concentrations up to 30% lower than those of the diafiltration buffer.