9701 · 37.2
Gas/liquid chromatography — FAQ
Frequently asked questions for 9701 Gas/liquid chromatography. Direct answers first, then deeper explanation — then practise with marking.
What's the difference between Gas-Liquid Chromatography (GLC) and High-Performance Liquid Chromatography (HPLC)?
The main difference is the mobile phase. In GLC, the mobile phase is an inert gas, and the sample must be volatile. In HPLC, the mobile phase is a liquid solvent under high pressure, which allows it to separate non-volatile compounds that cannot be analysed by GLC.
Why is the column in GLC placed inside an oven?
The oven maintains a precise and uniform temperature for the column. This is crucial because temperature directly affects the volatility of the components and their retention times. Controlling the temperature ensures that results are reproducible and allows for temperature programming (gradually increasing the temperature) to improve separation of complex mixtures.
What does GC-MS stand for and why is it so powerful?
GC-MS stands for Gas Chromatography-Mass Spectrometry. It's a hybrid technique where the outlet of a gas chromatograph is fed directly into the inlet of a mass spectrometer. The GC separates the mixture into its individual components, and then the MS analyses each component as it elutes, providing a mass spectrum. This gives a 'molecular fingerprint' that allows for much more definitive identification than retention time alone.