Thin Layer Chromatography Practical

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TABLE OF CONTENTS

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Imagine one day you come across an unknown liquid, and you want to know what it is. Luckily, you are a scientist who has access to lab facilities. You know that in the lab you have a database of known Rf values for different substances, a pencil, a thin layer of paper and some solvent. So, what can you do with all of this? All of these materials alongside the situation points to carrying out thin-layer chromatography, and that is what we will be exploring in this article.

We will be exploring what thin-layer chromatography is.
Then we'll look at the principle of thin-layer chromatography.
We'll see what a thin-layer chromatography diagram looks like.
Finally, we will explore the method of thin-layer chromatography.

Thin-layer chromatography diagram

Thin-Layer Cromatography. Taken from: Wikimedia Commons

Fig. 1: Thin-Layer Cromatography. Taken from: Wikimedia Commons.

So, what exactly does a thin-layer chromatogram look like? If we look at the image on the right, we can see what is known as a chromatography tank. Inside the tank we can see the solvent, which is the mobile phase, the TLC plate which is the stationary phase and finally the solvent front, which shows how far the mobile phase has travelled.

Now, you may be thinking, what are all the coloured dots? These dots represent the different, separate components of a mixture. As the solvent front travels upwards, the mixture is separated and this is why they are all at different points on the plate. When two dots are on the same level, it shows that those two components from a mixture are identical.

Analysing a chromatogram

After carrying out the practical, we need to figure out what each component is. This can be determined using Rf values. There is a large database that contains known Rf values for different components. We use the chromatogram to find the Rf value, then use the database to determine the unknown components. We use the distance travelled by the mobile phase to determine the Rf value. The longer the distance travelled, the less the unknown compound has adsorbed to the stationary phase and allows us to explore the relative solubility of the unknown compound.

We use this equation to find the Rf value:

Rf = Distance travelled by the component ÷ Distance travelled by the solvent front

First, we measure how far the component has travelled. We do this by measuring the distance from the pencil line to the middle of the spot of the component. Next, we measure how far the solvent has travelled from the pencil line, which is also known as the solvent front. We then plug these figures into the equation above. The value we get is the Rf value of the component. We can then compare it to known values and determine what the component is.

Component	Rf Value
β-carotene	0.98
Chlorophyll a	0.59
Chlorophyll b	0.42

Let us say the solvent front has travelled 1.6 cm and the component has travelled 1.57 cm.

To calculate the Rf value, we just need to do the following:

$$\frac{1.57}{1.6}=0.98$$

Using the known values from the table above, we can determine that the unknown component is β-carotene.

Thin-layer chromatography uses

We can also explore the different uses of thin-layer chromatography:

To identify different components in a mixture.
To determine the extent of a reaction.
To determine the purity of a substance.

Thin-Layer Chromatography Practical - Key takeaways

Chromatography in general is a method in which we separate different components within a mixture.
For thin-layer chromatography, we rely on adsorption.
The principles of thin-layer chromatography are solubility and adsorption.
A thin-layer chromatogram has a plate, which is the stationary phase, a solvent, which is a mobile phase and the solvent front which is the distance which the solvent travels.
To analyse a thin-layer chromatogram, we determine each component's Rf value.
To work out the Rf value, we use the equation: Rf = Distance travelled by the component ÷ Distance travelled by the solvent front.
Thin-layer chromatography is used to identify different components in a mixture, determine the extent of a reaction and determine the purity of a substance.

References

Image of glass capillaries: real name: Nadina Wiórkiewiczpl.wiki: Nadine90commons: Nadine90, CC BY-SA 3.0 , via Wikimedia Commons

Frequently Asked Questions about Thin Layer Chromatography Practical

The principles of thin-layer chromatography are solubility and adsorption.

We first put the different components on a plate and put the plate in a solvent. Once the solvent has travelled near the top of the plate, we take it out and let it dry. We then analyse it to determine the unknown components.

It is an important technique that helps determine different components within a mixture.

It is mostly used in synthetic chemistry to identify different components within a mixture and determine their purity.

Final Thin Layer Chromatography Practical Quiz

Thin Layer Chromatography Practical Quiz - Teste dein Wissen

Question

What are some uses of thin-layer chromatography?

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Answer

To identify different components in a mixture

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Question

Why do we use capillary tubes?

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Answer

Small drops are required to prevent the different solutions from mixing

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Question

Why do we use gloves?

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Answer

Prevents any contamination

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Question

Why do we use a pencil?

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Answer

Used as it will not dissolve in the solvent

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Question

What does adsorbing mean?

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Answer

Adhesion of a molecule to a surface

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Question

What is a type of chromatography?

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Answer

Column chromatography

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Question

Calculate the Rf value if the solvent front has travelled 1.1 cm and the component has travelled 0.96 cm

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Answer

0.87

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Question

Calculate the Rf value if the solvent front has travelled 1.72 cm and the component has travelled 1.53 cm

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Answer

0.89

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Question

Calculate the Rf value if the solvent front has travelled 1.35 cm and the component has travelled 0.96 cm

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Answer

0.71

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Question

Calculate the Rf value if the solvent front has travelled 1.55 cm and the component has travelled 1.25 cm

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Answer

0.81

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Question

Calculate the Rf value if the solvent front has travelled 1 cm and the component has travelled 0.65 cm

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Answer

0.65

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Question

What do the different dots on a chromatogram signify?

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Answer

These dots represent the different, separate components of a mixture

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Question

Calculate the Rf value if the solvent front has travelled 1.8 cm and the component has travelled 1.3 cm

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Answer

0.72

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Question

Calculate the Rf value if the solvent front has travelled 1.2 cm and the component has travelled 0.87 cm

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Answer

0.72

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Question

Calculate the Rf value if the solvent front has travelled 0.9 cm and the component has travelled 0.45 cm

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Answer

0.5

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Thin Layer Chromatography Practical

Thin Layer Chromatography Practical

Thin Layer Chromatography Practical

Thin-layer chromatography diagram

Analysing a chromatogram

Thin-layer chromatography uses

Thin-Layer Chromatography Practical - Key takeaways

References

Frequently Asked Questions about Thin Layer Chromatography Practical

What is the principle of thin-layer chromatography?

How do you run a thin-layer chromatography experiment?

Why is thin-layer chromatography important?

Which of the given purposes is the thin-layer chromatography method most often used for?

Final Thin Layer Chromatography Practical Quiz

Thin Layer Chromatography Practical Quiz - Teste dein Wissen

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