AQA A Level Chemistry

Revision Notes

7.11.4 Gas Chromatography

Gas Chromatography

  • Gas-Liquid Chromatography (GLC) is used for analysing:
    • Gases
    • Volatile liquids
    • Solids in their vapour form
  • The stationary phase:
    • This method uses a long coiled column for the stationary phase
    • Normally a non-volatile liquid is the stationary phase in GLC
  • The Mobile phase
    • An inert carrier gas (eg. helium, nitrogen) moves the sample molecules through the stationary phase
  • The sample is injected into the column through a self-sealing disc and the vapour formed is carried through the stationary phase using the inert-gas mobile 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
    • It depends upon the attraction between the solute and the stationary and mobile phases as well as the volatility and nature of the solute
  • The retention times are recorded on a chromatogram where each peak represents a volatile compound in the analysed sample
    • The relative sizes (ie areas) of the peaks are related to how much of each compound is present in the mixture
  • Retention times are then compared with data book values to identify unknown molecules

Analytical Techniques - GLC Chromatogram, downloadable AS & A Level Chemistry revision notes

 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

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