GC-MS
Definition
Gas chromatography-mass spectrometry: a two-stage technique that separates the components of a mixture (GC) and then identifies each component by its molecular fragmentation pattern (MS). The standard confirmatory method for forensic drug and fire-debris analysis.
- Full name
- Gas chromatography-mass spectrometry
- Two stages
- GC separation followed by MS identification
- Standard use
- Confirmatory method for drugs and fire-debris analysis
Common questions
Why is GC-MS considered a confirmatory test rather than a screening test?+
Its mass spectral fragmentation pattern is compound-specific and compared against reference libraries, giving a high degree of identification certainty, which is why presumptive screening results (colour tests, immunoassays) are typically followed up with GC-MS before a finding is reported as confirmed.
What sample types is GC-MS unsuited for without modification?+
Compounds that are not volatile or thermally stable, such as many large or polar molecules, will not pass through the GC column intact, so they require derivatisation to make them volatile or an alternative technique such as LC-MS instead.
How does GC-MS handle a complex mixture like fire debris with many overlapping compounds?+
The GC stage separates the mixture in time before compounds reach the detector, and the MS stage then distinguishes co-eluting compounds by their differing mass spectra, together allowing an examiner to identify ignitable liquid residue patterns within a background of pyrolysis products.
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