Define Thin Layer Chromatography?
This is an improvement over paper chromatography and uses thin layers of slurried absorbents like silica gel, alumina, cellulose, Kieselguhr, modified celluloses and polyacrylamide on glass plate or plastic sheet. This facilitates the adhesion of the adsorbent to the plate, binding agents such as calcium sulphate is incorporated into the slurry. Sometimes, the slurry is mixed with fluorescent dye for compounds to fluoresce under UV light. The method of running the chromatography is almost the same as that of paper. The advantage of TLC over paper chromatography is the time required for development is considerably less and secondly the fineness of the adsorbent powder ensures very rapid capillary flow of the solvent along the layer of adsorbent and hence considerable sharpness of the spots from original.
The methods for detecting the spots are same as paper, with an added advantage of spraying with 25% H2SO4 or keeping the plate in iodine vapours. Both the methods are useful for qualitative and quantitative purposes.