# A forensic scientist uses gas chromatography-mass spectrometry (GC-MS) to identify an unknown substance found at a crime scene. Explain how GC-MS works to identify the unknown substance, including the role of each technique.

> Edexcel A-Level Chemistry (9CH0) — Topic 6 Modern analytical techniques · Explain · 5 marks

> Gas chromatography-mass spectrometry (GC-MS) is a modern analytical technique used to separate and identify substances in a mixture. It combines two separate processes to produce reliable identification of unknown compounds.

## Mark scheme (5 marks)

1. Gas chromatography separates the components of the mixture
2. Components travel through the column at different speeds / have different retention times
3. The separated components are fed into / pass into the mass spectrometer
4. The mass spectrometer identifies each component by producing a mass spectrum / fragmentation pattern
5. The mass spectrum / fragmentation pattern is compared to a database / library of known substances to identify the unknown compound

## Key terms

- [gas chromatography](https://www.gradenine.co.uk/glossary/gas-chromatography)
- [mass spectrometry](https://www.gradenine.co.uk/glossary/mass-spectrometry)
- [GC-MS](https://www.gradenine.co.uk/glossary/gc-ms)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-forensic-scientist-uses-gas-chromatography-mass-af5a7878) · Published by Druglandscape Ltd.