Don't rely to much on Rf, they are different from experiment to experiment (e.g. because of different activities of your plates or humidity in eluents).
I suggest to use Van Urk = Ehrlich reagent for the detection of indoles (p-dimethylaminobenzaldehyde in methanol / HCl conc., heat with hot air after immersion into the reagent, tryptamines give violet to blue -> gray spots) and two eluents, one acidic (few drops acetic acid added) and one basic (few drops triethylamine added). The basic tryptamines will have (greatly) different Rf, the nonbasic impurities (e.g. the very apolar skatoles) will have nearly the same Rf.