Which chromatography technique is primarily used for separating molecules based on their size?

Size Exclusion Chromatography is the technique specifically designed to separate molecules based on their size. This method utilizes a column packed with porous beads that allow smaller molecules to enter the pores, effectively increasing the path length they must travel and thus delaying their passage through the column. Larger molecules, on the other hand, cannot enter these pores and therefore move through the column more rapidly. This differential movement enables the separation of molecules with varying molecular weights, making Size Exclusion Chromatography particularly useful in purifying proteins, polysaccharides, and other macromolecules.

In the context of the other techniques listed, Thin Layer Chromatography involves separating compounds based on their different affinities to a stationary phase and a mobile phase rather than size. Hydrophobic Interaction Chromatography separates molecules based on their hydrophobicity, while Ion Exchange Chromatography relies on the charge properties of the molecules for separation. Each of these methods addresses different characteristics of molecules, which is why they do not focus on size as Size Exclusion Chromatography does.