Saturday, May 2, 2020

What are the types of paper chromatography?

Learn about five types of paper chromatography which is according to how the chromatogram is developed.

The principle involved in paper chromatography is partition chromatography. The paper chromatography has a stationary phase made of a special cellulose paper and is called chromatography paper. The mobile phase is either a solvent or combination of solvents. A sample mixture is spotted on a line approximately 2 cm over the base of the stationary phase and then suspended in a chromatography chamber that has the appropriate mobile phase. The mobile phase elevates the paper and flows at the spot through capillary action. The paper retains different molecules according to their affinity into two phases. After the development of chromatograms, the spots of the isolated compounds are apparent from the original location position on the chromatogram at varying heights. This can be seen either by the use of a suitable spray reagent or under ultraviolet light. The relative adsorption of each analyte of the sample is articulated as the retention factor (Rf value).
There are five types of paper chromatography are available on the basis of how the chromatogram is developed.
Ascending chromatography: In this type of paper chromatography, the chromatogram is ascending. The development of chromatogram takes place because of mobile phase upward moves on the paper. The mobile phase is at the bottom of the chamber. The tip of the paper with sample spots only dips to the bottom of the mobile phase thus the spots remain just above the mixture of solvents.
Descending chromatography: In this type of paper chromatography, for the development of paper, the solvent travels to the downwards of the paper. The mobile phase is placed at the top of the system and it moves by gravity.
Ascending - descending chromatography: In this hybrid version of paper chromatography, the mobile phase first flows up over a paper folded on rod and begins its travels to downward after crossing the rod. This process allows for long-term development for better resolution of complex sample mixtures.
Radial or horizontal mode: In this mode of paper chromatography, the mobile phase moves from the center towards the periphery of the circular paper. This is usually done in a covered petri dish for the development of chromatograms. The wick in the middle point of the paper is dipped in the mobile phase, by which the solvent is drained on the paper and radially transfers the sample as concentric rings to form sample spots of various components.
Two-dimensional chromatography: In this mode of paper chromatography, the chromatogram development arises at right angles to directions of the first run. The sample mixture is spotted in a corner of rectangular paper, followed by the paper for the second chromatogram is again immersed in the solvent at the right angle to the preceding development.

Commonly asked questions on chromatography are as follows.

What are the applications of paper chromatography?
Paper chromatography is a type of chromatography that is used for the isolation and identification of colored sample mixtures including pigments.
 
What are the steps in paper chromatography?
Steps involved in paper chromatography are preparation of the sample, spotting sample on the paper, development of chromatogram, drying of paper, and detection of molecules.
 
Which type of paper is used in paper chromatography?
The selection of the correct type of paper used is significant. Generally cellulose or filter paper is one of the most used as a stationary phase in paper chromatography.
 
What is the major difference between paper chromatography and TLC?
The major difference between paper chromatography and TLC is that the paper chromatography uses a paper as its stationary phase and TLC uses a thin layer of silica gel or alumina as its stationary phase.

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