Adsorption of BSA on QAE-dextran: equilibria

Area of Science:

• Biochemistry
• Surface Chemistry
• Materials Science

Background:

• Bovine serum albumin (BSA) is a key protein in biological systems.
• Ion exchange chromatography is a crucial technique for protein purification.
• Understanding protein adsorption on ion exchangers is vital for optimizing separation processes.

Purpose of the Study:

• To investigate the equilibrium adsorption isotherms of BSA on a QAE dextran-type ion exchanger.
• To determine the influence of pH and salt concentration on BSA adsorption.
• To elucidate the primary mechanisms governing BSA adsorption.

Main Methods:

• Experimental determination of equilibrium isotherms for BSA adsorption.
• Analysis of adsorption data using Langmuir and Freundlich models.
• Investigation of ion exchange contribution to adsorption.
• Evaluation of the effect of pH, NaCl concentration, and buffer solutions on adsorption.

Main Results:

• BSA adsorption isotherms were independent of initial BSA concentration but highly pH-dependent.
• Langmuir equation best described isotherms at pH ≥ 5.05, while Freundlich equation was suitable at pH 4.8.
• Ion exchange contribution was minimal (1% and 0.4% of exchange capacity at pH 6.9).
• BSA adsorption was mainly electrostatic at pH ≥ 5.05 and hydrophobic/hydrogen bonding at pH 4.8.
• NaCl presence shifted isotherms to the right; no adsorption occurred at 0.2 mol/dm³ NaCl.
• Adsorption from pure water showed higher capacity on HPO₄²⁻-form resin compared to buffered solutions.

Conclusions:

• BSA adsorption on QAE ion exchangers is predominantly governed by electrostatic interactions at neutral to alkaline pH.
• Hydrophobic interactions and hydrogen bonding play a more significant role at acidic pH near BSA's isoelectric point.
• Salt concentration significantly inhibits BSA adsorption, with complete suppression at 0.2 mol/dm³ NaCl.
• The choice of buffer and ionic form of the resin can influence BSA adsorption capacity.