C2 3.8 Instrumental analysis

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Key points and learning objectives:

How can we use gas chromatography to seperate compunds in a sample mixture?

Samples to be analysed are often mixtures of different compounds and they need to be seperated before they can be identified by instrumental techniques. To do this chemists have a developed a technique called gas chromatography-mass spectrometry (GC-MS). They use gas chromatography to seperate the compounds that are easily vapourised.

Seperation technique:

  • 1. Sample mixture is vapourised
  • 2. A carrier gas moves the vapour through the column (usually helium)
  • 3. The compounds have different attractions to the material inside the column. The compounds with stronger attractions to the column will take longer to get through the column. We say they have a longer retention time. The compounds that take a shorter amount of time to get throught the column have a


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