# Describe the principle and working of Thin Layer Chromatography

The technique of TLC was developed by Egon Stahl. It is example of partition chromatography.

In this case stationary phase is variety of coating material like Alumina, silica gel etc. They are to be activated after applying. The activation is done by heating to a temperature of 200°C. The activity of the adsorbent decreases if the temperature exceeds to 200°C.

Lamina or glass plate is thoroughly washed with water and chromic acid to remove soluble and insoluble impurities. The slurry of the activated adsorbent is applied. The slurry must contain 5-20% by weight of binder which is helping the slurry to remain on the surface of Lamina.
The common binders are starch or plaster of Paris. Starch is better because, it form more durable layer, and it permits the faster migration of mobile phase.

The slurry is applied in Lamina with the help of spraying machine. The slurry must be uniform in thickness of 0.15mm to 2mm with the help of micro pipette place the few drops of given solution which contain 0.1mg to 10mg per cm3 of sample.

The plate is then dried in the air or in the oven at the optimum temp. Now the plate is developed by putting it in the pot containing developing solvent. For ascending the plate must dip, then by capillary action the solvent will move up and will dissolve the solute.
And by descending, the solvent (eluant) is sprayed from the top and this solvent will dissolve solute the solution is obtained at the bottom in the pot.

From that solution we can have qualitative as well as quantitative analysis. If we know the distance traveled by solute and solvent, we can find out $${ R }_{ f }$$ value which is characteristics. So $${ R }_{ f }$$ value help us in qualitative analysis. $${ R }_{ f } =\frac { Distance\quad traveled\quad by\quad solute }{ Distance\quad traveled\quad by\quad solvent } = \frac { x }{ y }$$

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