Evaluation of kinetic models for biospecific adsorption and its implications for finite bath and column performance

Abstract

Dynamic models that could describe the adsorption of adsorbate onto ligand immobilized on porous or non-porous particles in batch and column systems, are presented and solved. Two different kinetic models (kinetic models 1 and 2) are used to describe the dynamics of the adsorption mechanism when β-galactosidase is adsorbed onto monoclonal antibody immobilized on porous silica particles. The differences in the theoretical predictions of the concentration of the adsorbate in the fluid of the finite bath obtained from kinetic models 1 and 2, are not significant and the agreement between experiment and theory is good. But the two different kinetic models lead to different estimates for the value of the pore diffusivity, and provide significantly different concentration profiles for the adsorbate in the pore fluid and adsorbed phases of the adsorbent particles of the batch system. The column results indicate that the differences in the breakthrough curves obtained from kinetic models 1 and 2, increase as the column length increases. Also, the concentration profiles of the adsorbate in the adsorbent particles obtained from kinetic models 1 and 2, are significantly different and their differences vary along the axial distance of the column. The results indicate that while it is a necessary condition for a kinetic model to describe properly the experimental overall mass-transfer resistance, this is not also a sufficient condition for the accurate determination of the adsorption mechanism and for the accurate estimation of the values of the rate constants and of the pore diffusivity. Furthermore, the differences in the concentration profiles of the adsorbate in the adsorbent particles, obtained from kinetic models 1 and 2, have important implications on the performance of the adsorption stage, as well as on the performance of the wash and elution stages. Experiments are suggested which could provide information that could significantly improve the model discrimination and parameter estimation studies for the determination of a proper mechanism for the dynamics of the adsorption step and of an accurate estimate for the value of the pore diffusivity. When the estimated value of the pore diffusivity is varied by ± 20%, the effect on the dynamic behavior of the batch and column systems can be appreciable. The effect on the dynamic behavior of the batch and column systems when the estimated value (from a correlation) of the film mass transfer coefficient is varied by ± 20%, is not significant. The batch adsorption of β-galactosidase onto anti-β-galactosidase immobilized on non-porous glass coated beads is found to be controlled by film mass transfer and the dynamics of the adsorption step. The batch model with a second-order reversible interaction mechanism for the adsorption step, provides theoretical predictions such that the agreement between experiment and theory is reasonable. When the estimated value (from a correlation) of the film mass transfer coefficient is varied by ± 20%, the effect on the dynamic behavior of the batch and column systems (having nonporous adsorbent particles) is not significant. Column experiments are suggested which could provide information, in addition to the information obtained from batch experiments, that could improve the model discrimination and parameter estimation studies for the determination of a proper mechanism for the dynamics of the adsorption step, in affinity adsorption systems involving non-porous adsorbent particles.