What is Paper Chromatography ?
There are different types of chromatography and one of them is paper chromatography. The entire procedure requires the use of a specialized paper, specifically, a cellulose filter paper that serves as a stationary phase where the separation of compounds happens.
In other words, paper chromatography is a method that makes use of a paper sheet or strip as an adsorbent in the stationary phase through which a particular solution is allowed to pass.
Unlike other types of chromatography, paper chromatography is inexpensive and can efficiently separate dissolved chemical substances according to their varying migration rates across a sheet of paper. Paper chromatography was discovered in 1943 by Synge and Martin. (1, 2, and 3)
Image 1: The image above explains the principles of paper chromatography.
Picture Source: wikimedia.org
Principle of paper chromatography
Paper chromatography is a powerful analytical tool that makes use of minute quantities of material. It involves partition chromatography in which the substances are partitioned between phases of liquid. One phase of liquid is water held in the filter paper’s pores.
The other phase is called the mobile phase that moves over the filter paper. The differences in the affinity towards the water cause the compounds in the mixture to separate. It also has something to do with the mobile phase solvents movement under the paper’s capillary action of pores.
Another possible reason is the adsorption chromatography that takes place between the solid and liquid phases – the stationary phase is the paper’s solid surface and the liquid phase pertains to the mobile phase. Although the majority of paper chromatography applications use the principle of partition chromatography. (2, 3, and 4)
Image 2: Paper chromatography is used in different industries.
Picture Source: slidesharecdn.com
Image 3: Paper chromatography is one of the procedures used to separate colors.
Picture Source: pulpandpaper-technology.com
Different types or modes of paper chromatography
- Ascending chromatography – The paper’s development takes place primarily because of the movement of the solvent/upward motion on the paper. The reservoir of the solvent settles at the beaker’s bottom part. The paper tip containing the sample spots dips into the solvent causing the spots to stay above the solvent.
- Descending chromatography – The development of paper happens because the solvent moves on the downward part of the paper, hence, the name descending chromatography. The reservoir of the solvent is at the top.
- Ascending-descending – It is a combination of the two modes – the solvent travels upward and eventually go down on the paper.
- Radial mode – The solvent migrates from the center going to the edge of the circular chromatography paper. It is contained in a covered Petri dish to allow the development of the chromatogram. The center of the paper has a wick that dips into the mobile phase in the petri dish wherein the solvent drains and migrate the sample to form sample sports of varying compounds in the form of concentric rings.
- 2-D chromatography – There development of chromatogram happens in two directions at right angles. The samples are spotted at a specific corner of the rectangular-shaped paper and let the chromatogram development to take place. The paper is immersed in the mobile phase at a right angle to the former development enabling the second chromatogram to happen. (4, 5, 6, and 7)
How is paper chromatography done?
The steps for paper chromatography are as follows:
- Choose the ideal development type – When it comes to choosing the type of development, some factors have to be considered like the complexity of solvent, mixture, and paper. The most commonly used is radial paper chromatography or ascending type as it is easy to handle and perform. Not to mention, the steps are straightforward and less time-consuming.
- Choosing the right filter paper – The choice of filter paper should be according to the pores’ size and quality of the sample.
- Sample preparation – The sample should be dissolved in an ideal solvent used in creating the mobile phase.
- Spotting the sample on the paper – with the aid of a capillary tube, the sample is spotted at the right position on the paper.
- Chromatography development – The paper is immersed in the mobile phase. The capillary action of the paper causes the mobile to move over the sample on the paper.
- Drying of paper and detection of the compound – After the development of chromatography, the next step is to dry the paper with the use of air drier. A detecting solution is sprayed on the chromatogram developed paper, which will, later on, dried to thoroughly detect the sample chromatogram spots. (5, 7, 8, and 9)
Uses of paper chromatography
- It is used to separate the mixture of polar and non-polar compounds.
- It is one of the methods used to separate amino acids.
- It is used to check organic compounds such as inspecting the presence of biochemical in urine.
- In the pharmaceutical industry, a paper chromatography is performed to determine a specific drug and hormone.
- It can be used to evaluate inorganic compounds.
- It is one of the methods used to check for the contents of cosmetics.
- Paper chromatography can be used in studying the fermentation and ripening process.
- It is used to detect the presence of contaminants in foods and drinks.
- It is used to detect adulterants.
- In biochemical laboratories, paper chromatography can be used to check the reaction of mixture.
- It is a tool useful in determining dopes and rugs in both animals and humans.
- It is essentially helpful in separating colored pigments from a mixture. Drops of colored pigment mixtures are put on the filter paper and submerged into a solvent in a jar. It slowly dissolves the molecules in the mixture as the solvent slowly rises up the paper. The rising up motion of the filter paper causes the molecules of each pigment to leave the solution causing the pigments to rise up at a varying level on the chromatography paper.
- Paper chromatography is used in pathology and forensic science, especially in DNA and RNA fingerprinting. It can also check the presence of chemicals or alcohol in the blood. (2, 6, 9, and 10)