Chromatography

In this presentation you will: 

Explore the chromatography process and the different types of chromatography.

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Chromatography

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

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

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Chromatography

Chromatography

Chromatography is a group of analysis techniques for separating mixtures.

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.

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Chromatography

Chromatography

All chromatography techniques have: • A stationary phase: normally a solid or a liquid fixed in a solid. This is the material where the mixture flows.

• 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

Chromatography

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

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.

Soluble in the mobile phase Soluble in stationary phase

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Chromatography

Paper Chromatography

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

A solvent is the mobile phase.

The filter paper absorbs the mixture.

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

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

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Chromatography

Question 1

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

A) Acetone B) Medical alcohol C) Water D) White spirit

Chromatography

Question 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.

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

Thin Layer Chromatography

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

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

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. Silica Gel

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Chromatography

Thin Layer Chromatography

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

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

The solvent rises up the plate, separating the mixture. The piece of paper in the solvent container helps to saturate the space above the solvent with solvent vapor.

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Chromatography

Thin Layer 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.

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

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Chromatography

Thin Layer Chromatography

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

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

Question 3

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

A) Paper filter.

B) Plastic plate.

C) Glass plate coated with silica gel.

D) A solvent.

Chromatography

Column Chromatography

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

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

Column 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.

Mixture In Individual Components Out The individual components are collected as the solvent drips from the bottom of the column.

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Chromatography

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

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Chromatography

Question 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.

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

Summary

After completing this presentation you should be able to :  Show knowledge and understanding about paper chromatography.  Show knowledge and understanding about thin layer chromatography.  Show knowledge and understanding about column chromatography.

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