Chromatography

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In this presentation you will: Explore the chromatography process and

the different types of chromatography.

Chromatography

In a single step process it can separate a mixture into its individual components.

Chromatography is probably the most powerful and versatile technique available to the modern analyst.

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Chromatography

The chromatographic techniques consist of flowing the mixture to be separated over a material that retains some components more than others.

So different components flow over the material at different speeds and separate.

Chromatography is a group of analysis techniques for separating mixtures.

Chromatography

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Chromatography

• A stationary phase: normally a solid or a liquid fixed in a solid.

This is the material where the mixture flows.

All chromatography techniques have:

Chromatography

• A mobile phase: a gas, liquid or any substance capable of dissolving the mixture, i.e., a solvent.

This sweeps the sample over the stationary phase.

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Chromatography

A component which is quite soluble in the stationary phase, will take longer to travel through it than a component that is not very soluble in the stationary phase, but very soluble in the mobile phase.

The phases are chosen such that components of the sample have different solubilities in each phase.

Chromatography

Soluble in stationary phase

Soluble in the mobile phase

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Chromatography

The filter paper absorbs the mixture.

When the filter paper gets in touch with the solvent, it absorbs it.

In paper chromatography, the stationary phase is a filter paper.

Paper Chromatography

The dissolvent then dissolves and sweeps the mixture throughout the length of the filter paper.

A solvent is the mobile phase.

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Chromatography

1

Which of the following solvents do you think would be appropriate to separate the components of a watercolor paint?

Question

A) Acetone

B) Medical alcohol

C) Water

D) White spirit

Chromatography

2

Paper chromatography could be used:

I. To compare samples of ink on forged checks.

II. To compare paint samples taken from crashed cars.

III. To obtain the samples of the components in a mixture.

Question

A) Only statements I & II are correct.

B) Only statements II & III are correct.

C) All three statements are correct.

D) None of the statements is correct.

Chromatography

Adsorbents are capable of accumulating gases, liquids, or solutes on the surface, i.e., without being absorbed.

Examples of adsorbents include silica gel, alumina and cellulose. In Thin Layer Chromatography silica gel is normally used.

Thin Layer Chromatography works in a similar way to the paper chromatography, but the separation of the mixtures is much faster.

Thin Layer Chromatography

The stationary phase consists of a thin layer of adsorbent material coating a glass or plastic plate.

Silica Gel

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Chromatography

The solvent rises up the plate, separating the mixture.

A small volume of sample solution is applied to the adsorbent surface and allowed to dry.

Thin Layer Chromatography

Then the plate is immersed in an appropriate solvent for development.

The piece of paper in the solvent container helps to saturate the space above the solvent with solvent vapor.

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Chromatography

Components of the samples will separate on the stationary phase according to how much they adsorb on the stationary phase versus how much they dissolve in the mobile phase.

Thin Layer Chromatography

After the solvent has evaporated, the components of the mixture are seen.

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Chromatography

Normally, the plates covered with silica gel containing a fluorescent indicator, are examined under ultraviolet light.

Thin Layer Chromatography

The identity of each spot can be determined by comparing its position with the position occupied by known substances under the same conditions.

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Chromatography

3

Which one of the following could be the stationary phase in a Thin Layer Chromatography?

Question

A) Paper filter.

B) Plastic plate.

C) Glass plate coated with silica gel.

D) A solvent.

Chromatography

In column chromatography, the stationary phase is a solid adsorbent that is placed in a glass column.

Column Chromatography

The mobile phase is a liquid that is added to the top and flows down through the column (by either gravity or external pressure).

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Chromatography

Because the different components in the mixture have different interactions with the stationary and mobile phases, they will be carried along with the mobile phase to varying degrees and a separation will be achieved.

Column Chromatography

The individual components are collected as the solvent drips from the bottom of the column.

Mixture In

Individual Components Out

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Chromatography

Not only can column chromatography be used to determine the number of components of a mixture, but it can also be used to separate and purify substantial quantities of those components for subsequent analysis.

Column Chromatography

The disadvantage of column chromatography is that it is difficult to set up the column properly.

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Chromatography

4

Column chromatography could be used:

I. To compare samples of ink on forged checks.

II. To compare paint samples taken from crashed cars.

III. To obtain the samples of the components in a mixture for further analysis.

Question

A) Only statements I & II are correct.

B) Only statements II & III are correct.

C) All three statements are correct.

D) None of the statements is correct.

Chromatography

Show knowledge and understanding about paper chromatography.

Show knowledge and understanding about thin layer chromatography.

After completing this presentation you should be able to :

Summary

Show knowledge and understanding about column chromatography.

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