Fitting competitive adsorption isotherms to the experimental distribution data in reversed-phase systems

Area of Science:

• Analytical Chemistry
• Separation Science
• Physical Chemistry

Background:

• Understanding the adsorption behavior of phenolic compounds is crucial for environmental remediation and separation processes.
• Octadecyl silica is a common stationary phase in chromatography, and its interaction with analytes is well-studied.
• Phenol, resorcinol, and o-cresol are common organic pollutants with varying chemical structures.

Purpose of the Study:

• To determine the distribution isotherms of phenol, resorcinol, and o-cresol between aqueous methanol solutions and an octadecyl silica adsorbent.
• To evaluate the applicability of different adsorption isotherm models (Langmuir, Jovanovic, quadratic) for single-component and multi-component systems.
• To investigate the effect of methanol concentration on adsorption behavior and isotherm model fitting.

Main Methods:

• Preparation of aqueous solutions with varying methanol concentrations (0-40%).
• Determination of single-component and multi-component distribution isotherms using octadecyl silica.
• Fitting experimental data to Langmuir, Jovanovic, and quadratic adsorption isotherm models.
• Analysis of the influence of mobile phase composition on isotherm coefficients using polynomial equations.

Main Results:

• Single-component adsorption data were well-described by Langmuir or Jovanovic isotherms.
• Competitive Langmuir isotherm moderately described phenol-o-cresol mixtures in 20-40% methanol.
• Jovanovic and quadratic isotherms provided better fits for phenol-resorcinol mixtures.
• Adsorption isotherm model fitting generally improved with increasing methanol concentration.
• Isotherm coefficient dependencies on methanol concentration followed second-degree polynomial equations.

Conclusions:

• The choice of adsorption isotherm model is dependent on the specific mixture of phenolic compounds and methanol concentration.
• Increasing methanol concentration in the mobile phase enhances the predictability of adsorption behavior using established isotherm models.
• The study provides valuable insights into the chromatographic separation of phenolic compounds on octadecyl silica in hydro-organic mobile phases.