Question

Method of chromatography in which negatively charged molecules are selectively released from the stationary phase by positively charged molecules in the mobile phase is termed:

• A. Affinity chromatography
• B. Ion-exchange chromatography
• C. Adsorption chromatography
• D. Size-exclusion chromatography

Hint:

Separation by net electrical charge, with elution driven by competing ions.

Answer 1

The Correct Option is B

Step 1: Identify the separation principle in the stem. The molecules are separated based on their net electrical charge. The stationary phase holds charged molecules, and they are displaced (eluted) by other charged species in the mobile phase. Charge-based separation points to ion-exchange chromatography.
Step 2: In ion-exchange chromatography the stationary resin carries fixed charged groups. A cation-exchange resin carries negative groups and binds positively charged molecules; an anion-exchange resin carries positive groups and binds negatively charged molecules. Bound molecules are released by increasing salt concentration or by competing ions of the same charge in the mobile phase. This exactly matches the description of negatively charged molecules being released into the mobile phase.
Step 3: Rule out the distractors. Affinity chromatography separates by specific biological binding, such as antigen to antibody or enzyme to substrate, not by charge. Adsorption chromatography separates by differential surface adsorption (polarity), not charge exchange. Size-exclusion (gel filtration) chromatography separates purely by molecular size, where larger molecules elute first, again not by charge.
Step 4: Since charge-based binding and competitive elution define the technique, the answer is ion-exchange chromatography (option B).