# A student uses paper chromatography to identify the amino acids present in a sample of protein hydrolysate. After running the chromatogram, the paper is sprayed with ninhydrin solution to reveal the spots. Explain how the student can use the finished chromatogram to determine whether any of the amino acids in the sample are the same as those in a known reference mixture.

> Cambridge International IGCSE Chemistry (0620) — 12.3 Chromatography · Explain · 4 marks

> Amino acids are colourless and must be located using a locating agent such as ninhydrin. A reference mixture containing five known amino acids is run alongside the protein hydrolysate sample on the same chromatogram.

## Mark scheme (4 marks)

1. Calculate / measure the Rf value for each spot in both the sample and the reference mixture
2. Rf is the distance travelled by the spot divided by the distance travelled by the solvent front
3. Compare the Rf value(s) of spots in the sample with the Rf value(s) of spots in the reference mixture
4. If the Rf value of a spot in the sample matches that of a spot in the reference mixture (under the same conditions), the amino acid is identified as the same

## Key terms

- [chromatogram](https://www.gradenine.co.uk/glossary/chromatogram)
- [reference mixture](https://www.gradenine.co.uk/glossary/reference-mixture)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](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-student-uses-paper-chromatography-to-89063fab) · Published by Druglandscape Ltd.