Gas Chromatography (A2 Only)
Chemistry: AQA A Level, topic 6.10.4
Gas Chromatography
Gas chromatography (GC) is another type of chromatography.
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Experimental setup
- A column is packed with a solid.
- A mixture of the vaporised sample is passed through the column in an inert carrier gas under pressure at high temperature.
- The sample needs to be a gas, liquid or volatile solid to be carried through the column.
- The high temperature causes the sample to vaporise.
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Mobile and stationary phases
- The mobile phase is the inert carrier gas.
- The stationary phase is the solid in the column.
- The most volatile substances will elute from the column first as they will spend more time in the mobile phase.
GC-MS
GC-MS is gas chromatography coupled with mass spectrometry.
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Use of a mass spectrometer
- Mass spectrometry identifies the components of a mixture from their m/z values.
- It can analyse the substances in a mixture, but they must be separated first.
- So the GC can separate the substances in the mixture.
- The MS can then identify each substance eluted.
Adding a mass spectrometer
- Mass spectrometry can be used alongside gas chromatography to increase the analysis of a substance.
- It is simply done by attaching a mass spectrometer to the GC apparatus.
The two work well together
- Gas chromatography is good at separating substances in a mixture but bad at identification.
- Mass spectrometry cannot separate substances but is very good at identifying them.
- The two can be used together to play to both of their strengths.
The process in GC-MS
- A mixture is added to the gas chromatographer as usual.
- Each substance eluted from the GC is then directly analysed by a mass spectrometer using their m/z values.
Test yourself on Gas Chromatography (A2 Only)
Why is a high temperature necessary in the GC?