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Mobile-Phase Contributions to Analyte Retention and Selectivity in Reversed-Phase Liquid Chromatography: 1. General
Andreas Steinhoff1, Alexandra Höltzel1, Ulrich Tallarek1
1Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, Marburg 35032, Germany.
The Journal of Physical Chemistry. B
|June 13, 2025
Summary
Understanding analyte retention in chromatography requires examining the mobile phase's elution strength. Higher elution strength, driven by organic solvents, reduces analyte retention by altering stationary phase solvation.
Area of Science:
- Analytical Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- Reversed-phase liquid chromatography (RPLC) separates analytes based on their partitioning between a nonpolar stationary phase and a polar mobile phase.
- Analyte retention in RPLC is primarily controlled by the mobile phase's elution strength, typically adjusted by varying the water-organic solvent (W-OS) composition.
- Understanding the molecular-level interactions governing this process is crucial for optimizing chromatographic separations.
Purpose of the Study:
- To investigate the molecular mechanisms underlying analyte retention changes in RPLC with varying mobile phase elution strength.
- To elucidate the role of stationary phase solvation and analyte partitioning in response to mobile phase composition.
- To provide a molecular-level perspective on the relationship between mobile phase parameters and chromatographic retentivity.
Main Methods:
- Molecular dynamics (MD) simulations were employed to model a C18 stationary phase within a slit-pore system.
- The solute benzene was used as a model analyte to track its interactions and distribution.
- Spatially resolved contact analysis was performed to quantify bonded-phase and solvent contacts and analyte density distribution.
Main Results:
- Analyte partitioning and adsorption were found to be highly sensitive to the local water density within the stationary phase.
- Increasing mobile phase elution strength (higher organic solvent fraction) led to a decrease in water density near the stationary phase interface.
- This resulted in a shift of analyte environments away from the bonded phase and towards the bulk mobile phase, reducing bonded-phase contacts and thus retention.
Conclusions:
- Analyte retention in RPLC is fundamentally governed by the solvation of the stationary phase by the mobile phase.
- Changes in mobile phase elution strength directly influence stationary phase solvation, altering analyte partitioning and retentivity.
- Molecular dynamics simulations offer valuable insights into the molecular basis of chromatographic separation mechanisms.
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