If two substances on the same TLC plate have the same Rf value, what does this indicate?

When two substances on the same Thin Layer Chromatography (TLC) plate have the same Rf value, this indicates that they travel the same distance relative to the solvent front during the chromatography process. The Rf value, or retention factor, is calculated based on the distance traveled by the substance divided by the distance traveled by the solvent front.

If two different substances exhibit identical Rf values under the same experimental conditions, it suggests that they exhibit similar interactions with the stationary phase and the mobile phase. Since different substances typically have distinct Rf values due to their unique chemical properties, such as polarity and solubility, sharing the same Rf value strongly points towards the possibility that they are, in fact, the same substance. This conclusion is often reinforced by other analytical methods if further confirmation is required.

While it is theoretically possible for different substances to exhibit the same Rf value due to similar properties or behaviors under specific conditions, this circumstance is generally uncommon in practice, particularly if the TLC is conducted under standardized conditions.