# A student carries out paper chromatography to identify the amino acids present in a protein hydrolysate. After running the chromatogram, the student calculates the Rf value for each spot. Explain how the student would carry out the chromatography experiment and how Rf values are used to identify the amino acids present.

> Eduqas A-Level Chemistry — 3.7 Spectroscopy and chromatography · Explain · 5 marks

> Paper chromatography can be used to separate mixtures of compounds. Each compound travels a different distance up the paper depending on how strongly it is attracted to the stationary phase compared to the mobile phase. An Rf value can be calculated for each compound using: Rf = distance travelled by spot ÷ distance travelled by solvent.

## Mark scheme (5 marks)

1. A baseline (start line) is drawn in pencil near the bottom of the chromatography paper and the protein hydrolysate sample is spotted onto it.
2. The paper is placed in a suitable solvent so that the solvent level is below the baseline, and the solvent (mobile phase) travels up the paper.
3. The chromatogram is removed before the solvent reaches the top, the solvent front is marked, and the positions of the separated amino acid spots are marked.
4. The Rf value is calculated by dividing the distance travelled by the spot by the distance travelled by the solvent front.
5. The Rf values calculated are compared to known / reference Rf values for amino acids to identify which amino acids are present.

## Key terms

- [chromatography](https://www.gradenine.co.uk/glossary/chromatography)
- [Rf value](https://www.gradenine.co.uk/glossary/rf-value)

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- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-paper-chromatography-ad265963) · Published by Druglandscape Ltd.