gas chromatography

• what is the stationary phase in gas chromatography?

  viscous liquid or solid
• what is the mobile phase in gas chromatography and examples?

  unreactive carrier gas such as nitrogen or helium
• gas chromatography method:

  • inject sample into carrier gas
  • carried through tube over stationary phase
  • mixture dissolves in stationary phase, evaporates into mobile, then redissolves as they travel through the tube
• retention time: time taken to reach detector (in gas chromatography)
• what does the solubility of each component determine?

  how long it spends dissolved in the stationary phase and how long it spends moving along the tube in the mobile phase
• higher solubility, more time dissolved, longer to travel through tube to detector
• analysing gas chromatogram:

  • each peak corresponds to substance with retention time
  • use reference table to identify substance from retention time
  • area under each peak proportional to amount of each substance in original mixture (not height)
• limitations:

  • similar compounds have similar retention times, so a mixture of two substances may only produce one peak
  • need reliable reference retention times to identify substance
• Gas chromatography-mass spectrometry:

  • separate sample using gas chromatography
  • instead of detector, fed into mass spectrometer
  • produces mass spectrum for each component
• high pressure liquid chromatography-mass spectrometry:

  • stationary phase is a solid
  • mobile phase (solvent) and mixture pushed through column under high pressure (allows faster separation)
• uses of gas chromatography-mass spectrometry:

  • forensics- identify unknown substances on victims or what started fire
  • airport security- look for specific substances
  • space probes- examine rocks
  • environmental analysis- track pollutants or pesticides in foods