Why do different substances travel different distances on a TLC plate?

Substances that are attracted strongly to the polar stationary phase move slowly. Substances more soluble in the solvent move further.

Where is chromatography used in industry and forensic science? Give three examples.

A forensic chemist identifies drugs in a seized powder. A food chemist checks the dyes in sweets, and a pharmaceutical chemist checks the purity of a product.

How is a TLC plate prepared for a chromatography experiment?

A baseline is drawn in pencil about 1 cm from the bottom. Small, concentrated spots of each sample and reference are applied along it with a capillary tube.

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Analytical Chemistry Techniques

Thin-layer chromatography and its uses

3 things to know
A2 9

Overview

Stationary and mobile phases, how components separate, where chromatography is used, preparing and running a TLC plate, two-way chromatography, and high-performance liquid and gas chromatography.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is chromatography?

Key term

Why is chromatography described as a method of identifying substances?

Key term

What are the stationary and mobile phases in thin-layer chromatography?

Questions from this subtopic

Each one with the model answer underneath.

1
What is chromatography?
Model answer
Chromatography separates the components of a mixture by how they distribute between a stationary phase and a mobile phase. The components travel at different rates and so separate.
2
Why is chromatography described as a method of identifying substances?
Model answer
Each substance travels a characteristic distance under set conditions. Comparing a spot with a known reference shows what the substance is.
3
What are the stationary and mobile phases in thin-layer chromatography?
Model answer
The stationary phase is a thin layer of silica gel or alumina on a glass, plastic or aluminium plate. The mobile phase is a solvent that moves up the plate by capillary action.
4
Why do different substances travel different distances on a TLC plate?
Model answer
Substances that are attracted strongly to the polar stationary phase move slowly. Substances more soluble in the solvent move further.
5
Where is chromatography used in industry and forensic science? Give three examples.
Model answer
A forensic chemist identifies drugs in a seized powder. A food chemist checks the dyes in sweets, and a pharmaceutical chemist checks the purity of a product.
6
How is a TLC plate prepared for a chromatography experiment?
Model answer
A baseline is drawn in pencil about 1 cm from the bottom. Small, concentrated spots of each sample and reference are applied along it with a capillary tube.

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