Artificial Colours - Chromotography

Artificial Colours - Chromotography

1. Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food.

2. Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, eg water. As the solvent soaks up the paper, it carries the mixtures with it.

   • Different components of the mixture will move at different rates. This separates the mixture out.

3. Rf value

   • Rf = distance moved by the compound ÷ distance moved by the solvent
   • The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

4. Paper Chromatography is a separation technique that is used to separate and identify the components of a mixture (see also gas chromatography). Paper chromatography is used to identify colouring agents (chemicals) for example in food or ink.

5. The distance travelled up the paper by a component divided by the distance travelled up the paper by the solvent is called the Rf value or retention factor

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