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.

Thin‑layer chromatography (TLC) is first used to separate the components of the juice. The sample is spotted on a silica gel plate and developed in a suitable solvent system. After drying, the plate is examined under UV or by staining and the position of each spot is measured.

The Rf value of any spot that appears in the sample is calculated as the distance travelled by the spot divided by the distance travelled by the solvent front. The Rf value of the spot that is suspected to be the artificial sweetener is then compared with the Rf value of a reference sample of the pure sweetener that has been run on the same plate under identical conditions. A match of Rf values indicates that the sweetener is present in the juice.

Nuclear magnetic resonance (NMR) spectroscopy is then applied to the juice sample. The spectrum is recorded, giving the number of distinct proton environments as a series of peaks with characteristic chemical shifts and multiplicities.

The pattern of peaks in the juice spectrum is compared with the known ^1H‑NMR spectrum of the artificial sweetener. If the chemical shifts, integration and splitting patterns agree, the sweetener can be confirmed to be present.

An advantage of NMR over TLC is that NMR provides detailed structural information about the molecule, allowing unambiguous identification, whereas TLC only gives an Rf value which can be coincident for different compounds.