Thin Layer Chromatography - TLC

Thin Layer Chromatography

·        Chromatography is basically a technique used in the laboratory for the separation of mixtures.

·        Thin Layer Chromatograpgy(TLC) comes under Adsorption type of chromatography in which stationary phase is a solid and the mobile phase can be a liquid or a gas.

·        In this technique separation of components takes place on the basis of their Adsorption Coefficients.

The Procedure involves following steps :-

1) Preparation of Chromatoplate :-

·        Generally a slurry of silica gel or alumina in chloroform or carbontetra chloride is prepared.

·        A little of calcium sulphate is added to it which acts as a binding agent.

·        A thin layer of this slurry is applied on a Glass Slide by immersing the slide in the slurry.

·        The thin layer is made uniform by using another glass plate.

·        This prepared glass plate is called as Chromatoplate.

2) Application of sample on Chromatoplate :-

·        A very dilute solution of the sample is prepared by dissolving the sample in some suitable solvent.

·        This solution is applied on the chromatoplate with the help of capillary in the form of drop.

·        2-3 drops of sample are applied on it.

·        The direct contact of the capillary with the thin layer is avoided to prevent the damaging of the thin layer.

3)  Development Procedure :-

·        Now the chromatoplate is placed in a rectangular developing jar containing developing solvent at it’s bottom.

·        The three sides of the developing jar are lined with solvent immersed filter paper strips.

·        The top is covered tightly.

·        After the developing solvent has reached almost the another end of the chromatoplate, the chromatoplate is taken out of the developing jar.

·        During this development the different components of the sample gets separated according to their adsorption coefficients.

      4) Identification of components :-

·        On drying the chromatoplate the different components appear in the form of coloured spots.

·        If they are not visible then the chromatoplate is exposed to UV radiations or concentrated acids or strong oxidising agents can be sprayed on it.

·        The identification is done by determining the R_f value of the component as :-

·        R_f  = Distance travelled by solute / Distance travelled by solvent

Applications of TLC :-

·        TLC is widely used for qualitative analysis of organic and inorganic solvents.

·        TLC is also used for identification of compounds in drugs , biochemicals etc.

·        With TLC one can detect trace pesticides in water.

·        In forensic laboratory, as an analyst to identify the presence of drugs , poisons etc.

·        This technique can be used for the separation of components.

·        TLC can also used to check the purity of the sample.

Advantages of TLC :-

·        TLC is faster,superior,versatile and reproducible technique than Paper Chromatography.

·        It can be carried out with minimum sample just 0.1% .

·        Due to solid used as stationary phase the spots remain compact and does not spread.

·        Seperations are sharper in TLC.

·        Development time is shorter

·        Equipments used are simple.

Disadvantages of TLC :-

·        TLC cannot serve as record or proof whereas PaperChromatography can serve as records.Due to adsorption of components on silica gel some catalytic reaction may take place.