In normal-phase TLC, which compounds move fastest up the plate?

In normal-phase TLC, which compounds move fastest up the plate?

• A. Nonpolar compounds
• B. Polar compounds
• C. Aromatic compounds
• D. Aliphatic compounds

Answer: (A)

In normal-phase TLC the stationary phase is polar (like silica) and the mobile phase is relatively nonpolar. Separation relies on how strongly a compound interacts with the polar surface. Nonpolar compounds interact weakly with the polar stationary phase, so they spend more time moving with the solvent and travel farther up the plate, giving larger Rf values. Polar compounds, by contrast, form stronger interactions with the stationary phase and are retained longer, moving more slowly. So the fastest-moving compounds are the nonpolar ones.

In normal-phase TLC the stationary phase is polar (like silica) and the mobile phase is relatively nonpolar. Separation relies on how strongly a compound interacts with the polar surface. Nonpolar compounds interact weakly with the polar stationary phase, so they spend more time moving with the solvent and travel farther up the plate, giving larger Rf values. Polar compounds, by contrast, form stronger interactions with the stationary phase and are retained longer, moving more slowly. So the fastest-moving compounds are the nonpolar ones.