What is the principle behind thin-layer chromatography (TLC)?

Thin-layer chromatography (TLC) operates on the principle of separating compounds based on their polarity. In TLC, a stationary phase (usually a polar adsorbent like silica gel) is coated on a flat, inert surface, and a mobile phase (a solvent) is allowed to travel up the plate via capillary action. The components of the mixture being analyzed interact differently with the stationary phase and the mobile phase depending on their polarity.

Polar compounds will have stronger interactions with the polar stationary phase, causing them to travel more slowly up the plate. In contrast, nonpolar compounds will interact less with the stationary phase and will move more quickly with the solvent front. This difference in interaction is what leads to the separation of the compounds as they progress up the TLC plate.

Ultimately, the resulting spots on the plate indicate the differing polarities of the compounds in the mixture, enabling identification and analysis. Therefore, the correct choice highlights the fundamental mechanism of TLC, which is the separation of compounds based on their polarity.