Q.23 Which of the following separation processes is/are based on molecular size?
(A) Size-exclusion chromatography
(B) Ion exchange chromatography
(C) Membrane ultrafiltration
(D) Ultracentrifugation
Size-exclusion chromatography, membrane ultrafiltration, and ultracentrifugation separate molecules based on size, making options A, C, and D correct.
Correct Answer
Options A, C, and D: Size-exclusion chromatography, membrane ultrafiltration, and ultracentrifugation all rely on molecular size for separation.
Option Breakdowns
Size-Exclusion Chromatography (A)
Porous beads in the column allow smaller molecules to enter pores and elute later, while larger ones pass through quickly without interaction. This technique purifies proteins by hydrodynamic volume, independent of charge or affinity.
Ion Exchange Chromatography (B)
Molecules separate by charge interactions with oppositely charged stationary phases, not size—cation or anion exchangers bind based on net charge and elute via salt or pH gradients. Incorrect for size-based separation.
Membrane Ultrafiltration (C)
Membranes with specific molecular weight cut-offs retain larger molecules while smaller ones pass through, concentrating samples by size without chemical interactions. Commonly used for extracellular vesicles or protein prep.
Ultracentrifugation (D)
Differential speeds sediment particles by size and density—larger/heavier molecules pellet faster, separating via centrifugal force. A standard for biomolecule fractionation like viruses or organelles.
