Principle of ion-exchange chromatography Ion-exchange separations rely primarily on which interaction between solutes and the stationary phase?

Introduction / Context:
Ion-exchange chromatography (IEX) is a workhorse for protein, peptide, and small ion separations. Understanding its governing interaction guides buffer choice, pH, and salt gradients.

Given Data / Assumptions:

• Stationary phase bears fixed charges (e.g., sulfonate for cation exchange, quaternary ammonium for anion exchange).
• Analytes carry pH-dependent net charges.
• Mobile phase composition (salt, pH) tunes retention.

Concept / Approach:
The primary mechanism is Coulombic attraction: oppositely charged solutes bind to the stationary phase. Elution occurs by screening with salt (increasing ionic strength) or by changing pH to alter analyte charge.

Step-by-Step Solution:
Identify charge on stationary phase (cation or anion exchanger).Relate analyte net charge (function of pH) to binding strength.Select the option describing electrostatic attraction.

Verification / Alternative check:
Conductivity gradients cause predictable elution windows; pH titrations shift retention consistent with electrostatic binding theory.

Why Other Options Are Wrong:
Electrical mobility (option b) describes electrophoresis, not chromatography.Neutral adsorption (option c) fits normal-phase/adsorption chromatography, not IEX.Partitioning without charge (option d) fits partition chromatography, not IEX.

Common Pitfalls:
Confusing ion-exchange with capillary electrophoresis; ignoring the pH dependence of analyte charge.

Final Answer:
Electrostatic attraction between charged analytes and oppositely charged functional groups.