Question

Identify the correct statement with respect to gel permeation chromatography:

• A. Separation is based on the difference in size
• B. Smaller molecules are eluted faster than larger ones
• C. Stationary phase in GPC is a column filled with gel made of cellulose or silica
• D. It is widely used for the separation of small, low molecular weight, compounds

Hint:

In Size Exclusion Gel Permeation Chromatography, the elution order is backward compared to most methods: Big molecules elute first, small molecules elute last. The pores act as an obstacle course that only slows down the smaller components.

Answer 1

The Correct Option is A

Concept: Gel Permeation Chromatography (GPC), also called Size Exclusion Chromatography (SEC), is a method that separates molecules strictly according to their hydrodynamic volume or molecular size, rather than through chemical affinity or binding interactions.

Step 1: Evaluate Statement A The fundamental separation mechanism of GPC relies on a stationary phase containing porous gel beads with controlled pore size distributions. Molecules are separated based on whether they can enter these pores. Therefore, separation is based entirely on the difference in molecular size, making Statement A true.

Step 2: Evaluate Statement B In GPC, large molecules cannot fit into the internal pore network of the gel beads, so they are completely excluded. They travel exclusively through the interstitial space outside the beads and elute first from the column. Smaller molecules can enter the intricate pore paths, which increases their effective path length and retention time, causing them to elute later. Thus, statement B is false (larger molecules elute faster).

Step 3: Evaluate Statements C and D
• Statement C is inaccurate because GPC matrices typically use cross-linked organic polymers like polystyrene-divinylbenzene gels, rather than simple un-modified silica or cellulose.
• Statement D is incorrect because GPC is predominantly used to characterize high-molecular-weight systems, such as synthetic polymers, proteins, and large macro-biomolecules, rather than small, low-molecular-weight compounds.