In thin-layer chromatography, the retention factor ( _Rf_ ) is used to compare and help identify compounds. The _Rf_ value of a compound is equal to the distance traveled by the compound divided by the distance traveled by the solvent front (both measured from the origin). For example, if a particular compound travels 1.5 cm and the solvent front travels 6.0 cm, then the compound 's _Rf_ value is
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