Thin Layer Chromatography: Principle, Diagram, Applications, and Advantages

Thin layer chromatography (TLC) is an extraction technique that is used to separate organic compounds. It is a qualitative method based on the difference in polarities of the elements.

• TLC can be used to help determine the number of components in a mixture, the identity of compounds, and the purity of a compound.
• It is carried out on a TLC plate composed of a non-reactive solid coated with a thin layer of adsorbent material. This is the stationary phase.
• The sample is placed on the plate, and it is eluted with a solvent or solvent mixture known as the mobile phase (or eluent).
• This solvent then travels up the plate by capillary action. 
• As with any chromatography, certain compounds are more attracted to the mobile phase than to the stationary phase. 
• Therefore, various compounds travel along the TLC plate at various speeds and become separated. 
• To see colorless compounds, the plate is examined under UV light or stained.

Key Terms: Thin layer chromatography, Organic compounds, Solvent, Mobile phase, Non-reactive solid, Stationary phase, Hydroxyl groups, Aluminum oxide, Oxygen

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What Is Thin Layer Chromatography?

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Thin Layer Chromatography is a method used to isolate non-volatile mixtures.

• The experiment is carried out on a sheet of aluminum foil, plastic, or glass coated with a thin layer of adsorbent material.
• Aluminum oxide, cellulose, and silica gel are the most common materials used.
• Once the separation is complete, each component shows vertically separated spots.
• Each spot has a retardation factor (R_f) stated as follows:

R_f = distance. traveled by sample / distance traveled by solvent

The solvent system, the amount of material spotted, the adsorbent, and the temperature all affect the retardation factor. TLC is a fast, low-cost, simple, and easy chromatography method.

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Thin Layer Chromatography Principle

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Thin-layer chromatography is based on the principle of the relative polarity of the elements towards the mobile and stationary phases.

Materials such as silica gel, aluminum oxide, or cellulose can be used as a stationary phase in the separation of compounds, but silica gel is the most common choice.

• Silica gel is a solid network of silicon dioxide with atoms of silicon and oxygen alternating in all directions with hydroxyl (OH) groups on the surface.
• A substance with polar groups will be adsorbed on the stationary phase after interaction with the hydroxyl group.
• That will cause it to move slowly whereas, on the other hand, non-polar substances will not be attracted to the hydroxyl groups.
• It will allow them to move to the solvent front without being adsorbed to the stationary phase.

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Thin Layer Chromatography Diagram

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Thin Layer Chromatography Experimental Setup

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Before we begin the Thin Layer Chromatography Experiment, let us first know the different components necessary to carry out the method, as well as the phases involved.

Thin Layer Chromatography Plate

It is a thin rectangular piece of chemically inert and stable material such as plastic, glass, and aluminum foil. The stationary phase is applied to this thin layer chromatography plate in a uniform layer.

Thin Layer Chromatography Chamber

It consists of the development solvent i.e., mobile phase. It is closed during the procedure as the organic compounds are volatile and to keep the environment constant for the experiment without the interference of foreign materials.

Thin Layer Chromatography Mobile phase

The mobile phase is one that moves and is comprised of a solvent mixture or a solvent. This phase should be free of particulates. The development of spots improves with increased purity levels.

Thin Layer Chromatography Filter Paper 

It is dipped in the mobile phase and then used for analysis in the development chamber.

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Thin Layer Chromatography Procedure

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The following is the procedure to perform the thin-layer chromatography experiment

• A clean thin layer chromatography plate is coated with a thin and uniform layer of stationary phase, mostly the silica gel.
• The solvent mixture that needs to be analyzed is freshly prepared and poured into the development chamber.
• Along with it, the filter paper dipped in the mobile phase is also kept to maintain a uniform environment
• A line is marked at the bottom of the plate with the help of a pencil and the sample solution drops are spotted at this mark.
• The thin layer chromatography plate is then placed in the chamber and the lids are closed.
• It is made sure that the sample spots do not completely immerse in the solvent.
• The mobile phase travels up the thin layer chromatography plate through capillary action.
• The development appears in the form of spots.
• The plates are taken out and again a dotted line is marked till where the mobile phase has travelled.
• The plate is observed under UV light with the right precautions to visualize.
• The number of dots signifies the mixture of elements present in the compound.

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Thin Layer Chromatography Applications

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The following are the applications of Thin Layer Chromatography

Food Industry

Thin layer chromatography is used for the identification of various essential and volatile oils in various and determination of harmful chemicals in fruits and vegetables. It can also be used to separate and identify food coloring agents and preservatives.

Pharmaceutical Industry

Thin layer Chromatography is well known to be used for purity testing and analysis of active substances in various drugs such as sedatives, tranquilizers, and steroids.

Cosmetics

This separation and identification technique helps to keep our skin unharmed from the harmful chemicals used in different cosmetic products before they reach us by purifying the samples, making them fit for use.

Environmental Protection

It is widely used for analysis of groundwater and soil to maintain it healthy and protect against the degradation of the environment.

Chemistry

This method can also be used to determine the stage of a reaction. First, perform the experiment only with the reactants to get an idea of the starting material, then perform it again using a few drops of the solvent during the reaction, if the same mark appears with others then the reaction is going on, and if the same mark as the starting material does not appear, then the reaction is complete.

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Advantages Of Thin Layer Chromatography

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The following are the advantages of thin-layer chromatography

• Thin-layer chromatography is an easy and inexpensive method used for the separation or identification of elements in a compound.
• This method demands less equipment and the technique gives rapid analysis.
• All components can be easily visualized under UV rays.
• The components of even complex compounds separate easily.

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Disadvantages Of Thin Layer Chromatography

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The following are the advantages of thin-layer chromatography

• Thin-layer chromatography is only a qualitative technique and does not account for quantitative analysis.
• Although the lid of the development chamber is closed, factors such as changes in temperature and humidity are not accounted for in this experiment.
• The length of separation is limited as compared to other chromatography methods.
• UV rays are used for visualization of the elements, and it is harmful to the eyes. Minimal carelessness can lead to loss of eyesight.

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Things to Remember

• Thin layer chromatography (TLC) is a technique used for the separation of elements from a mixture of compounds.
• This method relies on the adsorption of elements based on their polarity on the stationary mobile phases.
• The stationary phase is a thin layer of silica gel applied on a thin layer of chromatography plate made of glass, plastic, or aluminum foil.
• The mobile phase is the mixture of solvents that moves up in the stationary phase through capillary action during the procedure.
• Thin-layer chromatography is used in different industries to identify and purify materials including the food industry, cosmetics, etc.

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