Which statement about TLC Rf values is true?

Which statement about TLC Rf values is true?

• A. 0 < Rf ≤ 1
• B. They can be negative
• C. They can exceed 2
• D. They are independent of the solvent

Answer: (A)

Rf is the ratio of how far a compound travels to how far the solvent front travels on a TLC plate. This distance ratio is dimensionless and, because the solvent front always moves at least as far as any spot, the spot cannot travel farther than the solvent front. That means Rf must be between 0 and 1. In practice, a compound that interacts strongly with the stationary phase moves very little and has a small Rf, while a compound that moves with the solvent has an Rf close to 1. Rf values depend on the solvent system and the stationary phase; changing the solvent changes how far the compound travels. So statements about negative values, values greater than 1, or independence from the solvent are not correct.

Rf is the ratio of how far a compound travels to how far the solvent front travels on a TLC plate. This distance ratio is dimensionless and, because the solvent front always moves at least as far as any spot, the spot cannot travel farther than the solvent front. That means Rf must be between 0 and 1. In practice, a compound that interacts strongly with the stationary phase moves very little and has a small Rf, while a compound that moves with the solvent has an Rf close to 1. Rf values depend on the solvent system and the stationary phase; changing the solvent changes how far the compound travels. So statements about negative values, values greater than 1, or independence from the solvent are not correct.