Question

Why is it important to compare the solvent height in the developing chamber with the location on the TLC plate where the spots are placed?

Answer 1

In TLC plate, we determine the ratio of the distance traveled by the spot of compound to the distance traveled by solvent front. This helps us understand that how fast the spot moves with the solvent. In the absence of adsorption on the stationary forces, the spot should move together with the solvent front. In such case, the distance traveled by the spot of compound will be equal to the distance traveled by solvent front. But due to adsorption from stationary phase, the distance traveled by the spot of compound will be less than the distance traveled by solvent front. The lesser distance represents the impact of strength of intermolecular forces of attraction between the spot and the stationary phase. This gauges the polarity of the compound.

In other words, the comparison of the solvent height with location on the TLC plate where the spots are placed gives approximaton about relative strengths of intermolecular forces of attraction between (1) compound spotted and stationary phase (material of TLC plate) and (2) compound spotted and solvent (mobile phase).