GCMS is an instrumental technique, comprising a gas chromatograph (GC) coupled to a mass spectrometer (MS), by which complex mixtures of chemicals may be identified and quantified.
This makes it ideal for the analysis of hundreds of relatively low weight compounds found in environmental samples.
The sample solution is injected into the GC inlet, where it is vaporized and swept onto the chromatographic column by the carrier gas (helium).
The sample then flow through the column, and the compounds comprising the mixture are separated by virtue of their relative interaction with the coating of the column (the stationary phase), and the carrier gas (the mobile phase).
Compounds eluting from the column pass through a heated transfer line, and into the source region of the MS. A beam of electrons ionizes the compounds, resulting in the formation of parent and fragment ions, the mass and abundance of which are determined by an ion trap MS.
Organic compounds must be in solution for injection into the gas chromatogram. Therefore, depending on the type of sample being analysed, one or more sample preparation procedures may be required. These procedures can range from simply dissolving some of the sample in a suitable solvent, to extensive extraction and clean up procedures.
For solid phase extraction of particulate matter (PM), a technique called accelerated solvent extraction (ASE) is employed, in which warm, pressurised solvents are used to extract the organic analytes. For water based samples, liquid-liquid extraction techniques are employed, such as portioning.
Once the sample is in solution, further sample clean up may be required by column chromatography.