Unifying sorption isotherms in reversed-phase liquid chromatography

Area of Science:

• Physical Chemistry
• Separation Science
• Surface Science

Background:

• Adsorption isotherm models are crucial for understanding chromatographic retention.
• Traditional models like Langmuir, BET, and GAB oversimplify interfaces, assuming uniform surfaces and site-specific adsorption.
• These assumptions contradict the heterogeneous nature of chromatographic interfaces and the dual role of adsorption-partitioning.

Purpose of the Study:

• To clarify the interactions governing chromatographic retention.
• To overcome limitations of traditional isotherm models with unrealistic assumptions.
• To develop a more comprehensive model for adsorption phenomena in chromatography.

Main Methods:

• Application of statistical thermodynamic fluctuation theory.
• Derivation of the ABC isotherm model from the theory.
• Reinterpretation of parameters from traditional models (Langmuir, BET, GAB) within the ABC framework.
• Analysis of sorbate-sorbate interactions to explain IUPAC isotherm types.

Main Results:

• The ABC isotherm captures mono-, di-, and tri-sorbate interactions.
• The ABC isotherm encompasses Langmuir, BET, GAB, and anti-Langmuir models as special cases.
• Sorbate-sorbate interactions are identified as key to elucidating IUPAC isotherm types (I, II, and III).
• Type I and III isotherms correspond to pure repulsion and attraction, respectively, while Type II exhibits concentration-dependent interaction changes.

Conclusions:

• The ABC isotherm provides a unified and accurate description of adsorption in chromatography.
• It resolves contradictions arising from idealized assumptions of traditional models.
• Understanding sorbate-sorbate interactions is essential for explaining diverse adsorption behaviors and chromatographic retention.