Describe the development of paper chromatogram.

Paper Chromatography was first employed by scientist Mikhail Tsvet in 1900. In 1952 A. Martin and R. Synge won the Noble prize in chemistry for the development of other Chromatographic techniques.

In paper chromatography the paper is important component. Several types of papers of different size, shapes, porosity and chemically treated are available in the market. Paper is randomly oriented cellulose fiber, cellulose is hydrophilic means solvent loving. Water or other polar solvents are tightly held by cellulose.

Development of chromatogram is also known as technique of paper chromatography. We take strip of paper used for chromatography. The length of strip must be 15cm. and breadth about 3.5cm. At 2cm. from bottom of paper, draw a pencil line. This is called base line or start line.

Small quantity of sample solution, is placed at start line. The water Present in the solution is dried in air. Now the sample on paper will appear like pimple or spot on the paper and this method of putting the sample is known as spotting.

Now this paper is hanged in the jar containing solvent (eluant) which is used for the extraction. It is important that the level of solvent remains below the base line. When the solvent travels from one end to the other end on the paper, the sample will also travel certain distance on the paper.

Later this paper is removed and dried. Different components of the sample travels different distances, thus mixtures are separated easily. This separation process is known as Development.

The development of the Solute from the paper can be done by:

1) Ascending development method.

In ascending paper chromatography the solvent is placed in trough at the bottom of the jar. The jar is filled with saturated vapor of the solvent. In this case the end of the paper strip is immersed in the organic solvent. The solvent rises up due to capillary action. The solvent when come in contact with the solute (spot) will get dissolve in the solvent forming the solution which is collected at the bottom in the pot (trough).

2) Descending development method.

When organic solvent is poured from top to bottom and while traveling down, it will come in contact with the solute, as the solute is readily soluble in organic solvent it dissolves forming solution which come down due to gravity and is collected in the trough (pot). The pot is taken out as the solvent is volatile will vaporize leaving behind solute which is analyzed.

3) Radial or circular paper method

In this case the sample is applied to the paper in the form of the spot at the centre of the circular paper. Due to the capillary action it moves radially towards the periphery. For the development a tank can be easily constructed using two Petridishes placed on one another. This circular paper is stretched between the two faces and the solvent is applied to the paper at the same point where the sample is applied by making a very small hole with the help of either cotton or wick (Twisted Thread).

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