37.1.2—Rf values

Rf is the distance travelled by a solute spot divided by the distance travelled by the solvent front, with both distances measured from the baseline.

Rf has no units and lies between 0 and 1. It helps compare a substance with a reference only when the stationary phase, solvent, temperature and measurement method are the same.

A spot that travels 2.4 cm while the solvent front travels 8.0 cm has Rf = 0.30. A second spot at 6.4 cm has Rf = 0.80, not 0.80 cm.

Do not measure from the paper edge or use the solvent-front distance as the denominator for one spot and the baseline distance for another.