Electrical double-layer models of ion-modified (ion-pair) reversed-phase liquid chromatography

Area of Science:

• Analytical Chemistry
• Separation Science
• Chromatography

Background:

• Reversed-phase liquid chromatography (RPLC) is a key separation technique.
• Ion-modified RPLC utilizes ionic modifiers to alter analyte retention.
• Existing models struggle to fully capture the complex interactions in ion-modified RPLC.

Purpose of the Study:

• To critically discuss stoichiometric models based on chemical equilibria.
• To introduce and analyze non-stoichiometric models considering the summed ionic influence.
• To evaluate chromatographic theories derived from the Poisson-Boltzmann equation.

Main Methods:

• Review and discussion of stoichiometric equilibrium models.
• Explanation of non-stoichiometric models focusing on collective ion effects.
• Analysis of Poisson-Boltzmann equation-based theories for ionic solute behavior.

Main Results:

• Stoichiometric models explain interactions via analyte-modifier equilibria.
• Non-stoichiometric models account for the total ionic environment's effect on solutes.
• Poisson-Boltzmann equation provides a quantitative framework for these summed influences.

Conclusions:

• Both stoichiometric and non-stoichiometric models offer insights into ion-modified RPLC.
• Non-stoichiometric approaches, particularly those using the Poisson-Boltzmann equation, provide a more comprehensive understanding of ionic solute behavior.
• Further critical discussion is needed to refine these theoretical predictions for practical applications.