GCMS: Gas Chromatography/Mass Spectrometry


What is GCMS?

Gas chromatography and mass spectrometry (GCMS) are two technologies, used together to find out what components are within a substance and in what quantities. It does this by separating out the components individually.

Each technology involved works differently to bring about the end result. Looking at each and how they interact with the other is important to understand how the GCMS process works.

How does the Gas Chromatograph work?

The inner workings of the GC are commanded by these components; heat inlet, an oven and a fused silica column.

Samples will be dissolved into a solvent and injected into the inlet port, where the liquid is vapourised. Once vapourised, the gas is carried through a column, with each substance being separated, due to the fact that some travel through the column at a slower pace (referred to as the retention time), as different substances may react differently to the stationary phase. The substances now enter the detector (the mass spectrometer) in the order they leave the column. Then a chromatogram graph is produced, giving the results.

How does the Mass Spectrometer work?

The mass spectrometer is used in tandem with the gas chromatograph, as a detector to give results from the test. The separated components that come from the GC, then have a beam of electrons passed through said component, creating electrically charged ions. This is done to each component, splitting them into ionised fragments. The atoms are ionised through displacing electrons to give positive ions. The fragments will produce results based on their size and charge. The ions are then accelerated and deflected by a magnetic field. When ions are being deflected, their mass will determine how much deflection they undergo. Heavier ions will have a harder time with deflection.The beam of ions will be detected electrically, by hitting a detection plate.

The MS will produce a graph called a mass spectrum, showing the fragments mass to charge ratio. The graph will give information, such as the ions “relative abundance” and “relative intensity”. The compounds are identified, due to the mass spectrum of a specific compound being the same every time it is analysed, which allows it to be identified.


Impact have an analytical lab capable of carrying out a range of testing for the GC/MS. For more information, contact us.