Eluent strength in liquid chromatography: What does this parameter primarily measure when comparing mobile phases?

Introduction / Context:
Eluent (elution) strength is a practical descriptor in normal-phase and reversed-phase method development. It quantifies how strongly a mobile phase can compete with analyte–stationary phase interactions to move analytes along the column.

Given Data / Assumptions:

• The term is linked to Snyder’s solvent strength concept and eluotropic series.
• Stronger eluents reduce retention factors (k) and shorten retention times.
• Comparisons are made for a specific stationary phase chemistry.

Concept / Approach:
In adsorption-dominated separations, eluent strength reflects the relative adsorption energy of the solvent on the stationary phase surface. A solvent with higher adsorption energy displaces analytes more effectively, weakening analyte adsorption and enhancing elution.

Step-by-Step Solution:
Relate eluent strength to competitive adsorption.Identify that “adsorption energy” (not bulk absorption, diffusivity, or mixing) is the correct underlying concept.Choose the option that names solvent adsorption energy.

Verification / Alternative check:
Empirical plots of log k versus solvent strength parameter show predictable retention changes, validating the concept for a given stationary phase.

Why Other Options Are Wrong:

• Absorption energy (b) refers to bulk uptake; chromatography is about surface adsorption in this context.
• Diffusivity (c) and mixing index (d) affect kinetics and system plumbing, not thermodynamic elution strength.

Common Pitfalls:
Applying a single solvent strength scale across different stationary phases; values are phase-dependent.

Final Answer:
solvent adsorption energy