# A conservation scientist wants to identify and separate the pigments present in a sample of ancient ink recovered from a historical manuscript. The scientist decides to use paper chromatography to analyse the sample. Explain how paper chromatography works and how it can be used to identify the pigments in the ink sample.

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

> The ancient ink sample is dissolved in a suitable solvent. A spot of the ink solution is placed at the bottom of a sheet of chromatography paper. A reference mixture containing three known pigments is also spotted onto the same paper. The paper is then placed in a beaker containing a small volume of solvent.

## Mark scheme (5 marks)

1. The solvent travels up the chromatography paper by capillary action
2. Different pigments have different solubilities in the solvent / different attractions to the paper, so they travel different distances up the paper
3. Each pigment produces a spot at a characteristic position / the Rf value for each pigment is constant under the same conditions
4. The Rf value is calculated as the distance travelled by the spot divided by the distance travelled by the solvent front
5. The Rf values of the spots from the ink sample are compared to the Rf values of the known reference pigments to identify which pigments are present in the ink

## Key terms

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

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- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-conservation-scientist-wants-to-identify-0d23a4e7) · Published by Druglandscape Ltd.