# A pharmaceutical company is developing a new painkiller. Quality control chemists use thin-layer chromatography (TLC) to check the purity of a synthesised compound. The synthesised compound is spotted onto a TLC plate alongside a reference standard of the pure compound and the plate is developed in a suitable solvent. The synthesised compound produces two spots on the developed TLC plate, whereas the reference standard produces only one spot. The chemists then use nuclear magnetic resonance (NMR) spectroscopy to investigate the impurity further. Explain what the TLC results indicate about the purity of the synthesised compound, and explain how NMR spectroscopy could be used to help identify the impurity.

> Edexcel A-Level Chemistry (9CH0) — 19.1 NMR and chromatography · Explain · 5 marks

## Mark scheme (5 marks)

1. The synthesised compound produces two spots, showing it contains two different substances / components
2. Each spot has a different Rf value because each substance travels a different distance relative to the solvent front, depending on its interaction with the stationary phase
3. The Rf value of one spot from the synthesised compound matches the reference standard, confirming which spot corresponds to the desired compound
4. NMR spectroscopy produces a spectrum showing peaks / signals at different chemical shifts, each corresponding to hydrogen atoms (protons) in different chemical environments
5. The number and position of peaks in the NMR spectrum can be compared to reference data / databases to identify the structure of the impurity

## Key terms

- [thin-layer chromatography (TLC)](https://www.gradenine.co.uk/glossary/thin-layer-chromatography-tlc)
- [nuclear magnetic resonance (NMR) spectroscopy](https://www.gradenine.co.uk/glossary/nuclear-magnetic-resonance-nmr-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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-pharmaceutical-company-is-developing-a-e012dcfd) · Published by Druglandscape Ltd.