Detection of Components - Thin Layer Chromatography (TLC)

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.

Example :      

(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.