DETECTION OF COMPONENTS
After development of TLC plates, the next important step is to detect the separated components so as to determine their respective Rf values.
(i) Coloured Substances : e.g., Xanthophylls, Chlorophylls, Carotenes, etc., may be located visually.
(ii) Colourless Substances : e.g., alkaloids, steroids, amino acids and the like may be detected under short-wave UV-light or a long-wave UV-light. These substances may also be detected as brown/dark brown spots when exposed to I2-vapours in a closed dessicator.
(iii) Specific Detecting Reagents : A few specific detecting reagents are normally used for a particular class of compounds e.g.,
Aniline-phthalate reagent :for carbohydrates ;
Ninhydrin reagent : for amino-acids, and
Dragendorff’s reagent :for alkaloids
(iv) Chromic acid/conc. H2SO4 : These corrosive reagents usually char the organic material on TLC plates and may be seen as dark brown spots.