[The new syllabus from 2015 has expanded the knowledge content for this topic, highlighted in colour]
Chromatography provides an important method of separating and identifying components in a mixture.
Separation depends on the balance between solubility in the moving phase and retention in the stationary phase.
Different types of chromatography are used depending on the composition of mixture to be separated.
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.
Retention times and Rf 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 Rf values with standards to identify different substances.
Assessment and practical opportunities
Students could use thin-layer chromatography to identify analgesics.
Students could use thin-layer chromatography to identify transition metal ions in a solution.
Separation of species by thin-layer chromatography.