Adsorption of Human Serum Albumin (HSA) on a mixed-mode adsorbent: equilibrium and kinetics

The adsorption equilibrium and kinetics of Human Serum albumin (HSA) onto a novel high particle density multimodal adsorbent were studied by batch adsorption experiments. MabDirect MM, from Upfront Chromatography A/S, is an agarose-tungsten carbide composite adsorbent with an anionic mixed mode ligand. The effects of ionic strength (by addition of salt) and of pH are assessed. Langmuir isotherms parameters are obtained along with pore diffusivity values by fitting the batch experiments using a pore diffusion model. Under the studied conditions for pH 5.0, without salt, it was obtained the largest adsorption capacity (36.0 ± 3.5 mg·g_{adsorbent,dry} ⁻¹) a typical behavior for a mixed mode adsorbent. Effective pore diffusivity (D_pe) was estimated as (2.2 ± 0.1) × 10⁻⁶ cm²·min⁻¹ for this condition. Additionally, the lowest adsorption capacity (8.6 ± 2.1 mg·g_{adsorbent,dry} ⁻¹) and an estimation of D_pe equal to (2.4 ± 0.6) × 10⁻⁶ cm²·min⁻¹ were obtained for pH 7.0 without salt. An alternative method of D_pe estimation is used and validate the results obtained by simulations. Furthermore, several experiments were carried out in a fixed bed column with the aim to understand the kinetics and hydrodynamics, and to validate the batch adsorption results. For a feed concentration of ±0.92 g·L⁻¹, pH 5.0, without salt, for cleaned and fresh adsorbent, fixed bed dynamic binding capacities of 13.84 and 14.37 mg·g_{adsorbent,dry} ⁻¹ were obtained, respectively, representing near 50% of saturation capacity.