# Mass spectrometry and infrared spectroscopy are two modern analytical techniques used to identify unknown compounds. Explain how a chemist could use both mass spectrometry and infrared spectroscopy together to identify an unknown organic compound, including what information each technique provides.

> Edexcel A-Level Chemistry (9CH0) — 7.1 Mass spectrometry and infrared · Explain · 5 marks

> A chemist has isolated an unknown organic compound from a reaction mixture and wishes to determine its identity using modern analytical techniques.

## Mark scheme (5 marks)

1. Mass spectrometry gives the molecular ion peak (M⁺), which gives the relative molecular mass of the compound.
2. Fragmentation pattern (fragment ions / fragmentation peaks) can be used to identify parts of the molecule or suggest its structure.
3. Infrared spectroscopy identifies functional groups present in the molecule because different bonds absorb infrared radiation at different (characteristic) wavenumbers / frequencies.
4. The infrared spectrum of the unknown compound can be compared to a database / library of reference spectra to confirm the identity of the compound.
5. Using both techniques together allows the chemist to determine both the molecular mass AND the functional groups present, giving a more complete / reliable identification of the compound.

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/mass-spectrometry-and-infrared-spectroscopy-are-041bfa6d) · Published by Druglandscape Ltd.