Interpretation of Chromatographic Retention Based on Electrostatic Theories

Abstract

Electrostatic potential is responsible for various phenomena, particularly for the behaviors of ionic species in solution and at various interfaces. In some modes of chromatography, electrostatic interaction often governs overall retention selectivity; ion-exchange chromatography is a typical example. Thus, though the understanding of electrostatic interaction is essential to interpret and predict chromatographic retention in some cases, sufficient attention has not been paid to its roles. There are some possible reasons for this situation: (1) direct estimation of the potential is usually difficult; (2) simple models not involving the contribution from electrostatic potential have given rather good explanations to experimental data. Some research groups have recently attempted to take electrostatic potential effects into consideration in various ways, and have successfully developed chromatographic models. These approaches are expected to facilitate understanding of chromatographic phenomena dominantly controlled by electrostatic interaction and to provide a view of more physical significance. In this review, the author mentions advantages of chromatographic models based on electrostatic theory over usual separated-phase models, and shows problems to be solved.

Molecular modeling and dynamics studies with explicit inclusion of electronic polarizability: theory and applications

“…Ion permeation across the cell membrane is tightly controlled by specialized proteins called ion channels [232-234]. In physical chemistry, ion solvation is also important in several processes such as chemical purification [235] and chromatographic systems [236] and ion-specific chelators [237]. …”

Ion Solvation Thermodynamics from Simulation with a Polarizable Force Field

“…For example, the transfer of ions between media obviously plays a critical role in the design of effective ion-exchange resins, used in chemical purification . A detailed understanding of the interactions of ions in solution is a major contributor to the understanding of selectivity and separation in chromatographic systems …”

Charge-Selective Aggregation Behavior of Thermoresponsive Polyelectrolytes Having Low Charge Density in Aqueous Solutions of Organic Counterions

“…The potential change of the polyelectrolytes upon the addition of charged species can be attributed to two possible factors: the shrinkage of the electric double layer (EDL) and charge cancellation by electrostatic adsorption on the charged surface. − For colloidal particles, their surface potential, Ψ, and surface charge density, σ, have the relationship as expressed in eq normalΨ = σ ε 0 ε κ ( 1 + 1 κ a ) where ε 0 is the vacuum dielectric constant, ε is the relative dielectric constant, and κ is the inverse of the Debye length expressed as κ = 2000 z 2 e 2 N A C ε 0 ε k T where z is the valence of the coexisting ion, e is the elementary charge, N A is Avogadro’s number, C is the ion concentration, k is the Boltzmann constant, and T is the absolute temperature . If there is no adsorption on the surface to change the surface charge density at the polymer surface, σ d can be considered to be constant throughout the experiment because the amount of counterions to cancel the polymer surface charges should be constant to neutralize the entire solution.…”