Dear Thien Duc,

Greeting and good morning,

TLC (Thin-layer chromatography) is used to determine the reaction product and the purity of compound. I think you should use other tests for the determination of aniline. For example, salt formation with acid, carbylamine reaction and bromine water reaction test.

Peptides like Alanine were initially analyzed by TLC, but you have to use a Ninhydrin spray for development of the spot.

You should be able to run aniline with hexane/ethyl acetate. Detection would by by UV light, use F254 plates and look for the dark spot. Run a spot of aniline by itself to see where it runs.