Rf value stands for retention factor. Retention factor is a chemical measurement that is the distance traveled by a compound divided by the distance traveled by a solvent.
In order to calculate Rf, you must first measure the distance traveled by a compound. Once that is recorded, measure the distance traveled by the solvent. Divide the distance traveled by the compound by the distance traveled by the solvent. For example, if a compound travels 6 centimeters and the solvent travels three centimeters, the Rf value would be two.
A compound's Rf remains constant throughout experiments as long as the solvent system, adsorbent, thickness of the adsorbent, amount of material spotted and temperature all remain constant as well. Because this rarely ever happens, Rf values are often referred to as relative Rf.
The calculation is important because it helps identify a compound. Generally speaking, compounds with the same Rf value turn out to be the same compound. Alternately, when two compounds have different Rf values, they can be identified as different. The larger a compound's Rf value, the greater its travel time on a TLC plate. As a result, a compound with a large Rf is less polar than one with a smaller Rf.
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