• 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 (e.g. 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 (i.e. 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

?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

Answers:

i)?D?(the larger the relative size of the peak, the greater the quantity of that substance present)

ii)?B?and?C?(the peak sizes are equal)

iii)?D?(the larger the retention time, the greater the interaction of that component with the stationary phase)