Identifying food additives

Identifying food additives

1. Chromatography.

   • Paper chromatography shows that the colourings in a food are those listed on the label.
   • When a solvent rises up the paper, it carries the colours with it and separates them.
   • Each chemical in a mixture travels up the paper at the same speed as it does when alone.
   • Chromatography is a separating technique also used with drugs in medicines.

2. Further chromatography.

   • To save time in analysing chromatograms, chemists use the retention factor (Rf)
   • Any chemical will always travel the same distance up a standard paper in the same time in the same solvent. the retention factor can be calculated like this: Rf =(Distance moved by the substance) divided by (distance moved by the solvent front).
   • Thin-layer chromatography uses a glass plate coated with a thin layer of absorbent materials. It is quicker than paper chromatography, but also more expensive.