GCMS: Gas Chromatography/Mass Spectrometry


What is GCMS?


Gas chromatography and mass spectrometry (GC-MS) are two technologies used together to determine and quantify volatile and semi-volatile organic molecules in a complex mixture by separating out the components individually based on their different retention times.

Each technology involved works differently to bring about the analytical results. Thus, it is important to understand how gas chromatography and mass spectrometry work individually.

How does the Gas Chromatograph work?

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

Samples will be dissolved into a volatile organic solvent and injected into the inlet port, where the liquid is vapourised. Once vapourised, the gas (H2) is carried through a column, with each substance being separated at different retention times depending on how they are retained by the stationary phase. Then, the analytes 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 high energy electrons, generated by the electron ionisation source (EI) set to 70 eV, with the consequent formation of 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 mass (m) and charge (z). 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. Finally, 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 (m/z). The graph will give information, such as the ions “relative abundance” and “relative intensity”. Therefore, the compounds of interest are identified due to their characteristic mass spectrum.

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