Chromatography can be used to separate and identify the components in a mixture.

Types of chromatography include:
- thin-layer chromatography (TLC) – a plate is coated with a solid and a solvent moves up the plate
- column chromatography (CC) – a column is packed with a solid and a solvent moves down the column
- gas chromatography (GC) – a column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature.

Separation depends on the balance between solubility in the moving phase and retention by the stationary phase.

Retention times and R_f values are used to identify different substances.

The use of mass spectrometry to analyse the components separated by GC.

Students should be able to:
- calculate Rf values from a chromatogram
- compare retention times and R_f values with standards to identify different substances.

Required practical 12

Separation of species by thin-layer chromatography.