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Types Of Chromatographic Techniques
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Paper chromatography
Paper Chromatography is one of the important chromatographic methods. Paper chromatography uses paper as the stationary phase and a liquid solvent as the mobile phase. Used to separate a mixture of solutes (or liquid) with different solubility and degree of adsorption. This method uses a porous or absorbant medium (e.g. paper or jel) and a solvent which can move over the material. This method is commonly used for separating a mixture of dyes in ink or different types of sugars (e.g. glucose, fructose, sucrose).dipped into a solvent.
In paper chromatography, the sample is placed on a spot on the paper and the paper is carefully The solvent rises up the paper due to capillary action and the components of the mixture rise up at different rates and thus are separated from one another
The principle involved can be partition chromatography or adsorption chromatography. Partition chromatography because the substances are partitioned or distributed between liquid phases. The two phases are water held in pores of the filter paper and the other phase is a mobile phase which passes through the paper. When the mobile phase moves, the separation of the mixture takes place. The compounds in the mixture separate themselves based on the differences in their affinity towards stationary and mobile phase solvents under the capillary action of pores in the paper. Adsorption chromatography between solid and liquid phases, wherein the solid surface of the paper is the stationary phase and the liquid phase is the mobile phase.
Procedure for Paper Chromatography
- Selecting a suitable type of development: It is decided based on the complexity of the solvent, paper, mixture, etc. Usually ascending type or radial paper chromatography is used as they are easy to perform. Also, it is easy to handle, the chromatogram obtained is faster and the process is less time-consuming.
- Selecting a suitable filter paper: Selection of filter paper is done based on the size of the pores and the sample quality.
- Prepare the sample:Sample preparation includes the dissolution of the sample in a suitable solvent (inert with the sample under analysis) used in making the mobile phase.
- Spot the sample on the paper:Samples should be spotted at a proper position on the paper by using a capillary tube.
- Chromatogram development:Chromatogram development is spotted by immersing the paper in the mobile phase. Due to the capillary action of paper, the mobile phase moves over the sample on the paper.
- Paper drying and compound detection: Once the chromatogram is developed, the paper is dried using an air drier. Also, detecting solution can be sprayed on the chromatogram developed paper and dried to identify the sample chromatogram spots.
Paper Chromatography Applications
There are various applications of paper chromatography. Some of the uses of Paper Chromatography in different fields are discussed below:
- To study the process of fermentation and ripening.
- To check the purity of pharmaceuticals.
- To inspect cosmetics.
- To detect the adulterants.
- To detect the contaminants in drinks and foods.
- To examine the reaction mixtures in biochemical laboratories.
- To determine dopes and drugs in humans and animals.
Types of paper chromatography:
- Ascending Paper Chromatography – The techniques goes with its name as the solvent moves in an upward direction.
- Descending Paper Chromatography – The movement of the flow of solvent due to gravitational pull and capillary action is downwards, hence the name descending paper chromatography.
- Ascending – Descending Paper Chromatography – In this version of paper chromatography, movement of solvent occurs in two directions after a particular point. Initially, the solvent travels upwards on the paper which is folded over a rod and after crossing the rod it continues with its travel in the downward direction.
- Radial or Circular Paper Chromatography – The sample is deposited at the centre of the circular filter paper. Once the spot is dried, the filter paper is tied horizontally on a Petri dish which contains the solvent.
- Two Dimensional Paper Chromatography – Substances which have the same rf values can be resolved with the help of two-dimensional paper chromatography.
- Partition chromatography is a process of separation of solutes utilizing the partition of the solutes between two liquid phases, namely the original solvent and the film of solvent on the adsorption This form of chromatography is based on a thin film formed on the surface of a solid support by a liquid stationary phase. Solute equilibriates between the mobile phase and the stationary liquid.