# A forensic scientist is analysing an unknown white powder found at a crime scene. She uses gas chromatography (GC) and mass spectrometry (MS) to identify the substances present. Describe how these two instrumental techniques are used together to identify the substances in the powder, and state two advantages of using instrumental methods compared with traditional chemical tests.

> Eduqas A-Level Chemistry — 2.8 Instrumental analysis · Describe · 5 marks

> Forensic laboratories routinely use instrumental analysis to identify unknown substances. Gas chromatography separates mixtures, and mass spectrometry identifies individual components by producing a fragmentation pattern that acts like a 'fingerprint' for each substance.

## Mark scheme (5 marks)

1. Gas chromatography separates the mixture into its individual components
2. Each component produces a different retention time / peak in the gas chromatogram
3. Mass spectrometry identifies each separated component by producing a fragmentation pattern (mass spectrum) unique to that substance
4. First advantage: instrumental methods are more sensitive / can detect very small amounts of a substance (trace amounts)
5. Second advantage: instrumental methods are more accurate / give more reliable results / can analyse very complex mixtures

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-forensic-scientist-is-analysing-an-10309937) · Published by Druglandscape Ltd.