In ion-exchange chromatography, the separation relies on

• A. Solubility
• B. Sign and magnitude of ionic charge
• C. Adsorption ability
• D. Molecular size

Answer: (B)

Ion-exchange chromatography separates compounds mainly by electrostatic interactions between the analyte’s charge and the fixed charges on the resin. The sign of the charge determines which type of exchanger will retain the molecule: positively charged species are retained on a cation-exchange resin with negatively charged groups, while negatively charged species are retained on an anion-exchange resin with positively charged groups. The magnitude of the charge matters too—the greater the charge (or charge density), the stronger the interaction with the resin, leading to longer retention and a need for stronger conditions (higher salt or pH shifts) to elute. This is why a protein or ion’s net charge at the operating pH drives its binding and elution behavior.

Other factors like solubility or molecular size aren’t the primary drivers for this technique, and while adsorption concepts relate to how the resin captures species, the key mechanism here is the electrostatic attraction based on charge.