Extension of Tóth Psi function from gas-solid to liquid-solid equilibria and application to reversed-phase liquid...

Area of Science:

• Physical Chemistry
• Surface Science
• Chromatography

Background:

• The Psi function, initially developed for gas-solid interfaces, was extended to liquid-solid interfaces.
• Reversed-phase liquid chromatography (RPLC) systems utilize hydrophobic silica adsorbents and aqueous-organic solvent mobile phases.
• Phenol is used as a probe compound to study adsorption phenomena in these RPLC systems.

Purpose of the Study:

• To investigate the applicability of the extended Psi function to liquid-solid interfaces in RPLC.
• To quantify the contribution of the Psi function and nonideal bulk liquid behavior to the total free energy of immersion.
• To determine the effect of phenol adsorption on interfacial tension in RPLC systems.

Main Methods:

• Dynamic frontal analysis (FA) was employed to measure phenol adsorption data.
• The minor disturbance (MD) method was used to measure excess adsorption of the organic solvent.
• UNIFAC group contributions were utilized to estimate activity coefficients in the bulk liquid phase.

Main Results:

• The Psi function successfully predicts approximately 90% of the total free energy of immersion at moderate phenol concentrations (< 10 g/L).
• At higher phenol concentrations, nonideal bulk liquid phase behavior contributes up to 30% to the total free energy of immersion.
• High concentrations of adsorbed phenol decrease interfacial tension by approximately 18 mN/m, irrespective of the adsorbed phase structure or organic solvent.

Conclusions:

• The extended Psi function is a valuable tool for understanding immersion free energy in RPLC systems.
• The nonideal nature of the bulk liquid phase must be considered at higher adsorbate concentrations.
• Phenol adsorption significantly reduces interfacial tension in RPLC, demonstrating a key characteristic of the interface.