What property primarily determines the speed of migration in normal-phase TLC?

What property primarily determines the speed of migration in normal-phase TLC?

• A. Polarity relative to mobile phase
• B. Molecular weight
• C. Polarity relative to stationary phase
• D. Boiling point

Answer: (C)

In normal-phase TLC, the separation hinges on how strongly a compound sticks to the polar stationary phase versus how much it dissolves in the mobile phase. Since the stationary phase is polar, a compound that is more polar relative to that surface will interact more and move slowly. Conversely, a less polar compound interacts less with the surface and rides along with the solvent front, moving faster. So the dominant factor shaping migration speed is the polarity of the compound relative to the stationary phase. Boiling point or molecular weight aren’t the primary drivers of this separation, and polarity relative to the mobile phase plays a role only insofar as it affects overall partitioning, but the key determinant in normal-phase TLC is how the compound interacts with the stationary phase.

In normal-phase TLC, the separation hinges on how strongly a compound sticks to the polar stationary phase versus how much it dissolves in the mobile phase. Since the stationary phase is polar, a compound that is more polar relative to that surface will interact more and move slowly. Conversely, a less polar compound interacts less with the surface and rides along with the solvent front, moving faster. So the dominant factor shaping migration speed is the polarity of the compound relative to the stationary phase. Boiling point or molecular weight aren’t the primary drivers of this separation, and polarity relative to the mobile phase plays a role only insofar as it affects overall partitioning, but the key determinant in normal-phase TLC is how the compound interacts with the stationary phase.