Question
Explain chromatography with diagram.
✓
Answer
Thin layer chromatography : Thin layer chromatography (TLC) consists of separating the components of a mixture on a thin layer of a adsorbent. In this technique, appropriate measurements of glass are placed on a plate of adsorbent (silica gel or alumina). We dry it thinly (approx. 0.2 mm thin). This is called layer chromatography plate. A small dot of the solution of mixture is placed in jar filled with eluent to some 2 cm height (Fig. 8.17). As the temperature of the leachate increases on the plate, the components of the mixture also rise up the plate along with the leachate but their rise varies depending on degree of adsorption. The speed of compound also varies depending on degree of adsorption. The speed of compounds also varies, due to which they get separated. The relative adsorption of different compounds is represented by Retardation factor $\left( R _{ F }\right)$.
The ratio of the distance travelled by a compound in a particular solvent system to the distance travelled by solvent is called retardation coefficient of that compound.
Hence $R _{ F }=\frac{\begin{array}{c}\text { Distance travelled by the compound } \\ \text { from baseline }(x)\end{array}}{\text { Distance travelled by solvent }}+$
or $\quad R _{ F }=\frac{x}{y}$
The $R_F$ value of each compound in a particular solvent system is fixed. Therefore, the compound can be identified if the $R_F$ value is known.
The ratio of the distance travelled by a compound in a particular solvent system to the distance travelled by solvent is called retardation coefficient of that compound.
Hence $R _{ F }=\frac{\begin{array}{c}\text { Distance travelled by the compound } \\ \text { from baseline }(x)\end{array}}{\text { Distance travelled by solvent }}+$
or $\quad R _{ F }=\frac{x}{y}$
The $R_F$ value of each compound in a particular solvent system is fixed. Therefore, the compound can be identified if the $R_F$ value is known.
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