# A pharmaceutical company uses paper chromatography to check the purity of a newly synthesised drug compound. After running the chromatogram, the solvent front has travelled 9.0 cm. The drug compound produces a single spot that has travelled 6.3 cm. A known pure sample of the same drug, run alongside it, produces a spot that has also travelled 6.3 cm. A technician concludes that the drug sample is pure. Explain how paper chromatography separates the components of a mixture and justify the technician's conclusion that the drug sample is pure.

> OCR A-Level Chemistry A (H432) — 6.3 Analysis (chromatography, NMR) · Explain · 5 marks

> Paper chromatography is routinely used in the pharmaceutical industry to check the purity of compounds. A stationary phase (paper) and a mobile phase (solvent) are used in the process.

## Mark scheme (5 marks)

1. The mobile phase (solvent) moves up the paper, carrying components of the mixture with it
2. Different components travel different distances because they have different attractions/affinities to the stationary phase and mobile phase
3. The Rf value of a substance is calculated as the distance travelled by the spot divided by the distance travelled by the solvent front
4. The Rf value of the drug sample matches that of the known pure sample (both 6.3/9.0 = 0.70), indicating they are the same substance
5. Only one spot is produced by the drug sample, which shows no other components are present, supporting the conclusion that the sample is pure

## Key terms

- [paper chromatography](https://www.gradenine.co.uk/glossary/paper-chromatography)
- [solvent front](https://www.gradenine.co.uk/glossary/solvent-front)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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/a-pharmaceutical-company-uses-paper-chromatography-4c1b2014) · Published by Druglandscape Ltd.