Steam volatile component volatilizes, the vapours condense in the condenser and the liquid collects in conical flask. Column Chromatography: Column chromatography involves separation of a mixture over a column of adsorbent (stationary phase) packed in a glass tube. The column is fitted with a stopcock at its lower end (Fig. .
). The mixture adsorbed on adsorbent is placed on the top of the adsorbent column packed in a glass tube. An appropriate eluant which is a liquid or a mixture of liquids is allowed to flow down the column slowly. Depending upon the degree to which the compounds are adsorbed, complete separation takes place.
The most readily adsorbed substances are retained near the top and others come down to various distances in the column (Fig. . ). The glass plate is then placed in a closed jar containing the eluant (Fig.
.12a). As the eluant rises up the plate, the components of the mixture move up along with the eluant to different distances depending on their degree of adsorption and separation takes place. The relative adsorption of each component of the mixture is expressed in terms of its retardation factor i.e. R f value (Fig.
. b). R f = Distance moved by the substance from base line (x) Distance moved by the solvent from base line (y) Fig. .
Column chromatography. Different stages of separation of components of a mixture. Thin Layer Chromatography: Thin layer chromatography (TLC) is another type of adsorption chromatography, which involves separation of substances of a mixture over a thin layer of an adsorbent coated on glass plate. A thin layer (about .2mm thick) of an adsorbent (silica gel or alumina) is spread over a glass plate of suitable size.
The plate is known as thin layer chromatography plate or chromaplate . The solution of the mixture to be separated is applied as a small spot about cm above one end of the TLC plate. The spots of coloured compounds are visible on TLC plate due to their original colour. The spots of colourless compounds, which are invisible to the eye but fluoresce in ultraviolet light, can