What is the formula for Rf?

What is the formula for Rf?

• A. Rf = (distance traveled by spot) / (distance traveled by solvent front)
• B. Rf = distance traveled by solvent front / distance traveled by spot
• C. Rf = distance traveled by spot
• D. Rf = (distance traveled by spot) / (distance traveled by solvent front)

Answer: (A)

Rf is the relative distance a compound travels on a TLC plate, expressed as a unitless ratio of how far the spot moves to how far the solvent front moves. This means the distance moved by the spot is divided by the distance moved by the solvent front, giving a value between 0 and 1 that reflects how far the compound rides relative to the solvent front. The best formulation is distance moved by the spot divided by distance moved by the solvent front. If you swap the order or leave out the solvent front distance, you either get a number that can exceed 1, or you lose the reference to how far the solvent carried the sample. For example, if the solvent front moves 5 cm and the spot moves 2 cm, the Rf is 2/5 = 0.4.

Rf is the relative distance a compound travels on a TLC plate, expressed as a unitless ratio of how far the spot moves to how far the solvent front moves. This means the distance moved by the spot is divided by the distance moved by the solvent front, giving a value between 0 and 1 that reflects how far the compound rides relative to the solvent front. The best formulation is distance moved by the spot divided by distance moved by the solvent front. If you swap the order or leave out the solvent front distance, you either get a number that can exceed 1, or you lose the reference to how far the solvent carried the sample. For example, if the solvent front moves 5 cm and the spot moves 2 cm, the Rf is 2/5 = 0.4.