Where should the solvent level be relative to the baseline in TLC development?

Where should the solvent level be relative to the baseline in TLC development?

• A. Below the baseline.
• B. Above the baseline.
• C. At the baseline.
• D. It doesn't matter.

Answer: (A)

In TLC development, the solvent level must be below the baseline because you want the sample spots to start dry at the origin while the mobile phase climbs up the plate. Keeping the solvent below the baseline prevents the spots from being wetted and dissolved right away, which would smear them and ruin separation. As the solvent front moves upward, components partition between the mobile phase and the stationary phase at different rates, producing distinct spots above the baseline. The baseline is the fixed origin used to measure how far each component travels to determine Rf values. If the solvent level were at or above the baseline, the spots would dissolve or wash away at the start, leading to poor separation and unreliable results.

In TLC development, the solvent level must be below the baseline because you want the sample spots to start dry at the origin while the mobile phase climbs up the plate. Keeping the solvent below the baseline prevents the spots from being wetted and dissolved right away, which would smear them and ruin separation. As the solvent front moves upward, components partition between the mobile phase and the stationary phase at different rates, producing distinct spots above the baseline. The baseline is the fixed origin used to measure how far each component travels to determine Rf values. If the solvent level were at or above the baseline, the spots would dissolve or wash away at the start, leading to poor separation and unreliable results.