# A food scientist is investigating whether a batch of fruit juice has been adulterated with an artificial sweetener. She uses two analytical techniques: thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy. Explain how each technique could be used to identify whether the artificial sweetener is present in the fruit juice sample, and state one advantage of using NMR spectroscopy over TLC for this analysis.

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

> Thin-layer chromatography separates components of a mixture based on how strongly they adsorb to a stationary phase compared to how well they dissolve in a mobile phase. NMR spectroscopy provides information about the number and chemical environment of hydrogen atoms in a molecule.

## Mark scheme (5 marks)

1. TLC separates the components of the fruit juice sample; the Rf value of any spot from the sample is calculated/measured
2. The Rf value of the sample spot is compared to the Rf value of a known reference/standard sample of the artificial sweetener run under the same conditions; a match indicates the sweetener is present
3. NMR spectroscopy identifies the number of distinct hydrogen (proton) environments in the molecule
4. The NMR spectrum of the sample is compared to the known NMR spectrum of the artificial sweetener; if the patterns of peaks match, the sweetener is confirmed as present
5. One advantage of NMR over TLC: NMR gives structural/molecular information about the compound (can confirm the identity of the molecule unambiguously), whereas TLC only gives Rf values which may coincide for different compounds / NMR does not require a reference standard to be run alongside

## Key terms

- [thin-layer chromatography (TLC)](https://www.gradenine.co.uk/glossary/thin-layer-chromatography-tlc)
- [NMR spectroscopy](https://www.gradenine.co.uk/glossary/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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-food-scientist-is-investigating-whether-5578c70d) · Published by Druglandscape Ltd.