21- Practical techniques - Chromatography

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Chromatography is a qualitative method

Technique that separates mixtures in order to detect components

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Process of chromatography

Chromatography separates components of a mixture using a solvent

Most common types are paper chromatography and thin layer chromatography

Both techniques work in similar way except thin layer chromatography uses thin coating of powder on glass plate

1- Small amount of mixture added to bottom of paper, which is just touching a solvent

2- Solvent moves up paper carrying components of mixture with it

3- Each component will bind to paper with different affinity

- Components with highest affinity at bottom of paper

- Components with lowest affinity at top of paper

- Components are separated according to different affinities

Distance travelled up paper by solvent = Solvent front

Each distance travelled by each component of mixture = Solute front

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Retention values

Each component of mixture has own retention (R1) values which identify compound

Can be worked out using formula:

R1 = Solute front/Solvent front

E.g. if solute travels up 10cm and solvent travels 15cm R1 value is 10/15 = 0.67

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Applications of chromatography

- Pharmaceutical - Test purity of products

- Environmental science - To test for pollutants

- Medicine - Blood processing and purification

- Forensic science - To identify compounds