Gas/Liquid Chromatography: Basics (CIE A Level Chemistry)

• 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

 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