Gas/Liquid Chromatography (Cambridge International A-Level Chemistry)

Gas/Liquid Chromatography Terminology

• Gas-Liquid Chromatography (GLC) is used for analysing:

  • Gases
  • Volatile liquids
  • Solids in their vapour form

• The stationary phase:

  • This method uses a column for the stationary phase
  • A non-polar, long-chain, non-volatile hydrocarbon with a high boiling point is mounted onto a solid support
  • Small silica particles can be packed into a glass column to offer a large surface area
  • Sample gas particles travel through this phase and are able to separate well due to the large surface area

• The Mobile phase

  • An inert carrier gas (eg. Helium, Nitrogen) moves the sample molecules through the stationary phase

Retention times

• Once sample molecules reach the detector, their retention times are recorded

  • This is the time taken for a component to travel through the column

• The retention times are recorded on a chromatogram where each peak represents a volatile compound in the analysed sample

• Retention times are then compared with data book values to identify unknown molecules

An example gas chromatogram

A gas chromatogram of a volatile sample compound has six peaks. Depending on each molecule’s interaction with the stationary phase, each peak has its own retention time