Solved example:
Methanolic extract of a medicinal herb Terminalia Arjuna bark powder was passed through a silica gel column and eluted by various solvents. Petroleum ether-ethyl acetate (10:1) eluant spotted on TLC where three components A, B and C corresponding to Rf values of 0.63, 0.72 and 0.79, respectively were observed. One of these compounds was a carboxylic acid which was identified as tartaric acid. In order to further confirm, a known standard tartaric acid was run on TLC where solvent front ran up to 8.6 cm and its spot was found at 6.3 cm. Which one of the spots corresponds to tartaric acid?
The Rf value for standard tartaric acid = 6.3/8.6 = 0.73
Thus, the standard value of 0.73 is comparable with 0.72 for B compound. Hence, B is tartaric acid.