What Is TLC (Thin-Layer Chromatography) And How Is It Useful for Quick Drug Identification And Reaction Monitoring?

The principle of TLC (Thin Layer Chromatography) is based on the differential affinity of components in a mixture toward a stationary phase and a mobile phase. As the liquid solvent (mobile phase) rises through the adsorbent layer—typically silica gel (stationary phase)—by capillary action, each component interacts differently with the two phases. Substances with a stronger affinity for the mobile phase migrate faster and travel farther up the plate, while those with a greater attraction to the stationary phase move more slowly, resulting in effective separation.

TLC is indispensable in reaction monitoring, qualitative identification, and rapid purity assessment. Its role in drug discovery and development is fundamental—many decisions in pharmaceutical R&D rely on simple yet powerful TLC results. Although considered a traditional chromatographic technique, TLC maintains a unique and irreplaceable position due to its reliability, simplicity, rapid results, and cost-effectiveness. Pharmaceutical development would be incomplete without it.

This article brings together practical, skill-based insights to strengthen your understanding of TLC. You will learn the underlying principle, key applications, advantages, limitations, method development strategies, case studies, and answers to frequently asked questions. By the end, your doubts will be cleared, and your knowledge of TLC will reach the next level.

What Is TLC (Thin-Layer Chromatography)?

Thin-layer chromatography comes under complete chromatography. It contains the solid stationary phase (coated on the plate) and the liquid mobile phase. Separation is governed by the polarity principle. In other words, separation depends upon the polarity of each analyte, the stationary phase and the mobile phase. A spot of the sample mixture is made on the TLC plate using a syringe or capillary tube, and the plate is placed in the TLC chamber containing the mobile phase. The mobile phase is moved over the TLC plate. Each Analyte of the sample mixture interacts with the mobile phase as well as with the stationary phase. During interaction, the stationary phase wants to retain the analyte, whereas the mobile phase wants to carry the analyte with it. The more polar compound retains more on the stationary phase (on the TLC plate) and moves slowly on the TLC plate compared to the nonpolar or less polar compound. Due to the difference in polarity, each compound interacts with the stationary phase and the mobile phase with different capacities, and they separate. The relative mobility of the compound is described by the R_f or Retention factor value.

R_f value or Retention factor value

R_f = Distance of the migration of the compound /Distance moved by the mobile phase

It is the ratio of the distance covered by the compound to the distance covered by the solvent (mobile phase).R_f value is unique for each compound under specific conditions, such as the stationary phase, temperature, thickness of the adsorbent layer, amount of the spotted material and the mobile phase used

Expert Tip: The R_f value is a decimal fraction, generally only reported to two decimal places

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7 Important Components of The TLC

The following are the different components of the TLC:

1. Thin Layer Chromatography Plates
2. Thin Layer Chromatography (TLC) Mobile phase
3. Thin Layer Chromatography (TLC) modifiers
4. Thin Layer Chromatography (TLC) chamber
5. Filter paper
6. Thin Layer Chromatography (TLC) syringe
7. Thin Layer Chromatography (TLC) UV chamber

Thin Layer Chromatography Plates

Commercial TLC plates are made of Aluminium and coated with a stationary phase like Silica gel or Aluminium oxide. A TLC plate can also be made using a glass plate or a plastic plate

1. Thin Layer Chromatography (TLC) Mobile phase

A solvent or a mixture of solvents with different polarities is used as the mobile phase. Generally, Hexane, heptane, chloroform, dichloromethane, ethyl acetate, ethanol, and isopropyl alcohol are used as solvents in the mobile phase. Acetic modifiers like formic acid, acetic acid and basic modifiers like ammonia, triethyl amine and diethyl amine are also used in the mobile phases based on the polarity of the analyte.

2. Thin Layer Chromatography (TLC) modifiers

: Acidic modifiers like formic acid, acetic acid and basic modifiers like ammonia, triethyl amine and diethyl amine are also used in the mobile phases based on the polarity of the analyte.

3. Thin Layer Chromatography (TLC) chamber

The TLC chamber is made of glass and it is used to develop the TLC plate. This maintains a stable environment during analyte spot development in the TLC process. It also prevents solvent evaporation and keeps the entire process dust-free.

5. Filter paper

It is used to equilibrate the TLC chamber.

6. Thin Layer Chromatography (TLC) syringe

It is required to apply the sample/standard spot on the TLC plate

7. Thin Layer Chromatography (TLC) UV chamber

• It is required to detect the analyte spot
• Colour development reagent: Reagents like Iodine vapour, Ninhydrin solution, KMnO4 solution and alkaline tetrazolium blue solutions are used for colour development

How to select the TLC solvents?

TLC can be operated in Normal phase chromatographic mode (NPC) and Reverse phase chromatographic mode (RPC). But it is widely used in NPC mode. The following solvents are widely used:

• Non-Polar Solvents (Hydrophobic)
  • Hexane (n-Hexane): Often used for non-polar compounds. It is commonly mixed with more polar solvents to adjust polarity.
  • Petroleum Ether: A mixture of hydrocarbons, often used for non-polar to moderately polar compounds.
  • Toluene: Slightly more polar than hexane and often used for moderately non-polar compounds.
  • Diethyl Ether: A low-polarity solvent, often used in mixtures with hexane or other solvents.
• Polar Solvents (Hydrophilic)
  • Ethyl Acetate: A relatively polar solvent used for moderately polar compounds, often in mixtures with non-polar solvents.
  • Acetone: Polar, good for separating compounds with moderate polarity.
  • Chloroform (CHCl₃): A moderately polar solvent, useful for separating a range of organic compounds.
  • Methanol (MeOH): Very polar, often used for highly polar compounds. Methanol is also commonly mixed with other solvents like chloroform, ethyl acetate, or water.
  • Water: Used in aqueous-based separations, often in combination with organic solvents.
• Mixed Solvent Systems
  • Hexane / Ethyl Acetate: A common mixture, where the ratio of hexane to ethyl acetate is adjusted based on the polarity of the compounds being separated. For example, a 9:1 mixture of hexane to ethyl acetate for non-polar compounds or a 1:1 mixture for more polar compounds.
  • Chloroform / Methanol: Often used for polar compounds, with varying ratios depending on the polarity of the analytes.
  • Hexane / Acetone: A mixture used for compounds with intermediate polarity, often in ratios like 7:3 or 9:1.
• Other Common Solvents or Mixtures
  • Dichloromethane (DCM): A moderately polar solvent, useful for a variety of organic compounds.
  • Hexane / Toluene: Used for non-polar to slightly polar compounds.
  • Acetonitrile (MeCN): A polar aprotic solvent, often used in gradient elution or in mixtures with other solvents.

Thin Layer Chromatography (TLC) Procedure

The following steps are involved in the TLC process;

• Make the point of spot application using a pencil. Keep in mind, TLC spots should be evenly spaced and should not sink into the mobile phase.
• Apply the sample to the marked spots TLC plate using a syringe or a capillary
• Transfer the mobile phase to the TLC chamber
• Place the moistened (with mobile) filter paper along the inside wall of the TLC chamber. It maintains equal humidity and prevents the edge effect.
• Insert the prepared TLC plate into the chamber with the sample spot facing the mobile phase.
• Close the chamber and allow sufficient time (about 40 to 60 minutes) to separate each analyte spot during TLC development
• Remove the TLC plate from the chamber and allow it to dry
• Analysed the spot using UV light or by colour development (using KMnO4 or Iodine vapour)
• Calculate the R_f value

How to develop the TLC Method?

In TLC, separation is governed by polarity. The mobile phase is selected based on the polarity of each analyte in the sample mixture. For polar molecules polar mobile phase is used, and for nonpolar molecules, non polar mobile phase is used. The following steps play an important role in TLC method development:

• Selection of the stationary phase
• Selection of the Mobile phase and
• Mobile phase optimisation

Selection of the stationary phase

Silica and Alumina are commonly used as the stationary phase in TLC. Therefore, the scope to play with the stationary phase during TLC development is limited.

Selection of the Mobile phase

The mobile phase is designed based on the polarity of each analyte in the sample mixture. Use

• Polar mobile phase for polar molecules
• Nonpolar mobile phase for nonpolar molecules
• Modifiers in the mobile phase to control the polarity

Generally, Hexane, heptane, chloroform, dichloromethane, ethyl acetate, ethanol, and isopropyl alcohol are used as the mobile phase. Acidic modifiers like formic acid, acetic acid, trifluoroacetic acid and basic modifiers like ammonia, triethyl amine and diethyl amine are added in the mobile phase based on the polarity of the analyte in the sample mixture.

Mobile phase optimisation

The composition of the solvent in the mobile phase is varied to get better separation between the spots.

• Increase the polar solvent (like ethanol, Isopropyl alcohol and Ethyl acetate) ratio to reduce/control the separation
• Decrease the polar solvent (like ethanol, Isopropyl alcohol and Ethyl acetate) ratio to increase the separation

How Is TLC Useful for Quick Drug Identification And Reaction Monitoring?

TLC is useful for quick drug identification and reaction monitoring because it provides fast, simple, and cost-effective separation of components. By comparing the Rf values and spot patterns of a sample with reference standards, drugs can be identified within minutes. During chemical reactions, TLC helps track the conversion of reactants to products by showing the appearance or disappearance of spots, allowing rapid assessment of reaction progress. Its speed, minimal sample preparation, and ease of visualisation make TLC ideal for routine pharmaceutical analysis.

Case study-1: Separation of N-(4-hydroxyphenyl)acetamide and 4-aminophenol by TLC

The following are the structures of Acetaminophen and 4-aminophenol:

From the above structure, it is clear that both compounds are polar, but 4-aminophenol is more polar compared to N-(4-hydroxyphenyl)acetamide.

• Selection of TLC stationary phase: A TLC plate containing Silica gel coating can be used
• Selection of mobile phase: Both 4-aminophenols are more polar compared to N-(4-hydroxyphenyl)acetamide, are contains -NH and -OH functional groups. Hence polar mobile phase with a basic modifier will be a suitable choice. For example, a mixture of Hexane/Heptane (non-polar) and Isopropyl alcohol/Ethanol (polar) with a basic modifier like Triethyl amine/ammonia solution can be used
• Mobile phase optimisation: Increase the ratio of nonpolar solvent and reduce the modfier to get better separation between the spots
• Final TLC condition: In the following TLC mobile phase condition, each spot of N-(4-hydroxyphenyl)acetamide and 4-aminophenol is well separated.
  • Final mobile phase: Hexane: Isopropyl alcohol: Triethylamine (90:10:0.05)

Case study 2: How to develop a TLC method for quantification of Tetrabutylammonium fluoride?

Method development approach:

• Molecular weight: C₁₆H₃₆FN
• Molecular weight: 261.46g/mol

Following is the structure of  Tetrabutylammonium fluoride

From the structure, it is clear that it is a quaternary ammonium salt. It does not have any chromophore, and secondly, it is an ionic compound. Therefore, it will neither be analysed on HPLC nor on GC.

The only possibility is to develop a qualitative TLC method. That is why widely qualitative TLC method is widely used for its content in Pharmaceutical substances.

In the following TLC condition, it is quantified up to 0.05% in the pharmaceuticals

TLC condition

• TLC plate: Silica Gel 60 F254
• TLC mobile phase: mixture of Dichloromethane and Methanol in the rat io of 88:12.
• TLC chamber: Vertical chamber saturated with 25% ammonium hydroxide solution
• Diluent: Dichloromethane
• Sample concentration: about 150mg/ml in Dichloromethane
• Standard: Tetrabutylammonium fluoride 0.05% ( weigh about 7.5 mg of Tetrabutylammonium fluoride and dilute to 100 ml with diluent)
• Injection volume: 5µl
• Run: about 10 cm
• Detection: iodine vapour about 25 to 30 minutes

TLC Procedure

Apply 5 µL of each standard and sample solution to the TLC plate and allow the spots to dry. Place the TLC plate in the equilibrated TLC chamber. Run the mobile phase up to 10 cm on the plate. Allow the plate to dry at room temperature in the hood. Then, put the TLC plate in the iodine chamber for 25 to 30 minutes. Compare the spot of Tetrabutylammonium fluoride in the sample with the standard Tetrabutylammonium fluoride.

TLC Troubleshooting

The following type of problem occurs during TLC analysis:

• Tailing in the analyte spot: If this problem occurs in the routine method, then there is an equilibration issue. Equilibrate the TLC system properly, and then this tailing issue will be resolved
• The analyte spot is not moving from the point of application. If this type of problem occurs in the regular method, then there is a problem of solvent evaporation from the mobile phase. Prepare the fresh mobile phase, equilibrate the TLC system properly and then this issue will be resolved
• Analyte does not retain on the TLC plate and moves with the mobile phase: If this type of problem occurs in the routine method, then there is a problem of mobile phase preparation. Prepare the fresh mobile phase, equilibrate the TLC system properly and then this issue will be resolved
• Distortion of the analyte’s spot: If this type of problem occurs in the routine method, then there is a problem in the mobile phase and the temperature of the lab. Prepare the fresh mobile phase, equilibrate the TLC system properly in temperature temperature-controlled environment and then this issue will be resolved

Advantages

The following are the TLC advantages:

• Selective technique with high separation power: Generally, normal phase TLC are used in the industries, and it is highly selective for qualitative analysis, like identification tests and purity tests.
• Simple technique: It is a simple technique and does not need any special skill. Anyone can perform the TLC .
• Inexpensive technique: It is cost cost-effective analytical technique. That is the reason TLC is backbone of every industry
• Quick analysis: TLC is known for its fast results. One can get a result within 10 to 40 minutes. That is why it is widely used in the monitoring of the reaction.
• Versatile technique: It is a versatile technique and can be used for various types of compounds, such as organic and inorganic compounds. For example content of Triethylamine and tetrabutyl ammonium bromide content in pharmaceuticals is performed by TLC
• High sensitivity: It is high sensitive instrument for qualitative analysis, like identification and purity test
• Sample recovery: The Sample can easily be recovered after TLC analysis since volatile solvents are used in the TLC
• Visualisation: Analyte spots can easily be seen in the UV chamber or by colour development
• Scale-up potential: The TLC technique can be used for scale-up after certain modifications
• Regulatory acceptance: The TLC technique is acceptable by all regulatory agencies in the world

Disadvantages

The following are the disadvantages of the TLC technique

• Quantitative analysis: Less suitable for quantitative analysis
• Detection limit or sensitivity: Sensitivity of the TLC is less than the other chromatographic techniques like HPLC/UPLC and GC
• Separation power: Limited stationary phases are available for the TLC and hence one can play only with the mobile phase during TLC development. That is the reason TLC has limited separation power.

What are the new advancements in TLC?

• TLC can also be performed in reverse phase chromatography mode (RPTLC). Now several new TLC plates containing C18 and C8 stationary phases are commercially available in the market.
• TLC is also used for Chiral purity using the chiral stationary phase.

RP-TLC stationary phase selection

TLC plates containing C18 and C8 stationary phases are used

RP-TLC stationary phase selection

Mixture of water and less polar organic solvents like tetrahydrofuran, methanol, ethanol, Isopropyl alcohol and acetonitrile are used.

Order of elution: Non polar analyte retin more compared to polar analyte

Advantages of RP-TLC

• Humidity does affect the result since mixture of aqueous and organic solvents are used
• Separation of analyte of different polarities such as nonpolar, less polar and extremely high polar can be possible
• RP-TLC results can be directly correlated with HPLC or UPLC
• Wide range of mobile phase selection availability and hence one can play a lot during mobile phase optimisation

Thin Layer Chromatography (TLC) Applications

TLC is widely used for monitoring the reaction, identification test, purity test, related substances test, impurity profile test, compound purification, pesticide residue test, genotoxic impurity test and content test in the following industries:

• Research and development centre
• Pharmaceutical industries
• Pharmaceuticals formulation
• Cosmetic industries
• Pesticide industries
• Food industries
• Biochemical industries
• Polymer industries and
• Testing laboratory

Conclusion

Despite some limitations, TLC is widely used for various tests like mentoring the reaction, identifications, purity, related substances in the pharmaceutical industries due to its reliability of the result, simplicity and cost effectiveness. Now I hope this post has cleared all your doubts related to TLC and you can apply it more effectively in pharmaceutical development. For any queries or suggestion related to this article write in the comment section or contact me using contact form.

TLC Interview FAQs

What is the thin layer chromatography used to separate?

TLC is used to separates compound from the sample mixture. It may be westside in cosmetic sample or genotoxic impurities in the pharmaceuticals.

What are the advantages of the thin layer chromatography?’

TLC is fast, simple and cost effective technique

How thin layer chromatography is more superior than other chromatographic methods?

Due to quick result, costeffetiveness and simplicity it is more superior than other chromatography like HPLC and UPLC

How do you perform thin layer chromatography?

Prepare the sample and a make sample-spot on the TLC plate. Develop the TLC in the TLC chamber and visualize the spot in UV chamber or by colour development

Can TLC be used for quantitative analysis?

Can be used but result will not be reproducible. TLC is mainly used for qualitative analysis

How long does it take to perform a TLC analysis?

TLC is a fast analysis band can be completed within an hour

Can TLC be used for analysing volatile compounds?

Not in all cases. But some of the volatile compounds like triethylamine is analyzed by TLC

Abbreviations

• TLC: Thin layer chromatography
• RPTLC: Reverse phase thin layer chromatography

References

• https://www.sigmaaldrich.com/IN/en/applications/analytical-chemistry/thin-layer-chromatography
• https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/thin-layer-chromatography