Thin layer chromatography involves the use of thin layer of some adsorbent as stationary phase coated on some inert support (such a glass or plastic sheet), while the solvent, the mobile phase percolates through the layer. Mixture to be analysed is deposited near the bottom of plate. The solvent is made to move up the plate.
As it passes over the deposit various components of the mixture are carried up and deposited as separate spots on the plate. The adsorbent commonly used are silica gel, alumina, Kieselgurh, Cellulose powder etc. while the choice of solvent depends on the solubility’s of constituents of the mixture. The R/values of various constituents may be calculated from the distances traversed by the spot and the solvent from the place of origin or the point where the mixture is deposited.
Thin layer chromatography, is therefore, similar to paper chromatography. Instead of filter paper, a thin layer of some adsorbent is used as the stationary phase. Thin layer chromatography has many advantages over paper chromatography. The technique is less time consuming and convenient. There is a greater sharpness of separation and a higher sensitivity.
The spots can be scrapped off with the help of a knife dissolved and analysed quantitatively by using suitable analytical techniques. Thin layer chromatography has proved to be very useful in the analyses of adulterated food stuffs, determination of organomercurials in fishes, phenolics and aromatic alcohols in beer, organochlorine and carbamate pesticides in fruits and vegetables.