Characterization of BSA adsorption on mixed mode adsorbent: I. Equilibrium study in a well-agitated contactor

STREAMLINE Direct HST (GE Healthcare Biosciences, 2004) is a newly designed mixed mode adsorbent, which contains small stainless steel particles and is based on a highly crossed-linked agarose with multi-modal functional groups. In this work, BSA (bovine serum albumin) was used as a model protein and the experiments were carried out in a well-agitated contactor under a variety of operating conditions, such as adsorption pH, conductivity, and hydrophobicity of the process liquids. The results showed that the Langmuir model seemed to successfully simulate the adsorption isotherm curves and the thermodynamic parameters (qmax and Kd) were little affected by the conductivity and hydrophobicity of the adsorption buffer. On the contrary, the adsorption pH had significant effects on these parameters due to the negatively charged repulsion between HST adsorbent and BSA molecule. The adsorbent for the adsorption of BSA is therefore based on the pH-dependent behavior of a dual-mode ionizable ligand. Moreover, the adsorbed BSA was eluted completely either by 10 mM sodium carbonate buffer (pH 12) or by 1 M NaCl (pH 7) and found to be more easily eluted by pH 12 buffer.