The coupling of the electrostatic potential with the transport and adsorption mechanisms in ion‐exchange chromatography systems: Theory and experiments

Abstract

The coupling of the electrostatic potential with the transport and adsorption mechanisms in ionexchange chromatography systems: Theory and experimentsThe coupling of the constitutive expression for the electrostatic potential as specified through Poisson's equation together with the constitutive equations for the mechanisms of convection, diffusion, electrophoretic migration, and adsorption provides the necessary set of constitutive expressions to be employed in the material balance equations of ion-exchange chromatography systems to construct macroscopic continuum models that could be used to design and simulate the dynamic behavior of systems involving a single charged adsorbate or multiple charged adsorbates. A physically relevant and consistent macroscopic continuum model that can predict, as has been observed experimentally by UV confocal microscopy (UVCM), the presence or absence of the concentration overshoot phenomenon, based on the pH and ionic strength of the liquid solution, is discussed and expanded to describe the behavior of IEC systems involving competitive adsorption of two or more charged adsorbates. Furthermore, UVCM and confocal scanning laser microscopy (CSLM) experiments and the macroscopic continuum models that could be used to analyze their data are indicated. Results are also presented that have been obtained from molecular dynamics (MD) modeling and simulation studies (microscopic modeling and analysis) employing realistic atomistic models derived from fundamental physics, and indicate the physical mechanisms that are relevant and actively involved in the transport and adsorption of charged adsorbates in IEC systems, as well as their relative importance. The results obtained from the MD simulations show that when a charged macromolecule is adsorbed it is restrained by a strong dominant Coulombic interaction and is trapped by a hydration layer adjacent to the surface and these lead to zero lateral displacement of the adsorbed macromolecule. This finding indicates that surface diffusion could be a physically implausible mechanism in IEC systems involving charged adsorbate macromolecules. Also, the results obtained from the MD simulation studies show that the transport coefficients that characterize the mass transfer of a charged adsorbate in the liquid solution by diffusion and electrophoretic migration have magnitudes along the lateral direction that are different from those along the direction that is normal to the charged surface.

An exclusion mechanism in ion exchange chromatography

“…The significance, under some conditions, of phenomena such as intra-pore electrophoretic transport is becoming more fully appreciated (e.g., Liapis and Grimes, 2005) as are the molecular level interactions responsible for such phenomena. Recent publications by Zhang et al (2004bZhang et al ( , 2005a provide example of the use of such simulations in ion exchange, and their application to complex systems similar to those studied here.…”

Protein adsorption in porous adsorbent particles: A multiscale modeling study on inner radial humps in the concentration profiles of adsorbed protein induced by nonuniform ligand density distributions

“…In order to obtain a proper and comprehensive understanding of the effect that a nonuniform spatial ligand density distribution could have on the concentration of the adsorbate molecules in the porous adsorbent particles, it is considered in this work that the adsorbate molecules are mixed with a sufficient excess of supporting electrolyte so that the electrophoretic effect vanishes [8,15,46]. Furthermore, the excess supporting electrolyte ensures that the activity coefficient of the diffusing electrolyte is effectively constant along the diffusion path [8,15,17,18,46].…”

“…Furthermore, the excess supporting electrolyte ensures that the activity coefficient of the diffusing electrolyte is effectively constant along the diffusion path [8,15,17,18,46]. Therefore, in the mathematical model presented in the following paragraphs of this section, the electrical phenomena [7 -15] are not being explicitly accounted for and it is taken that the adsorbate molecules are transported within the porous adsorbent particles by the mechanism of pore diffusion.…”

Design of Polymeric Porous Adsorbent Media and the Dynamic Behavior of Transport and Adsorption of Bioactive Molecules in Such Media

“…In stage III, the non-uniform distributions of charged species could result in an electric field that allows electrophoretic migration [9] to take place and contributes to the overall transport rate of the adsorbate biomolecule, which occurs by both thermal diffusion and electrophoretic migration. Therefore, it is more reasonale to describe the rate of biomolecular transport with an effective mass transport coefficient instead of a thermal diffusion coefficient.…”