Paper Chromatography

Paper chromatography

• Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

Paper chromatography process

1. Water and ethanol solution is heated

2. As the paper is lowered into the solvent, some of the dye spreads up the paper

3.The paper has absorbed the solvent, and the dye has spread further up the paper

Chromatography phases

• Chromatography relies on two different ‘phases’:

  • the stationary phase, which in paper chromatography is very uniform, absorbent paper
  • the mobile phase is the solvent that moves through the paper, carrying different substances with it

• The different dissolved substances in a mixture are attracted to the two phases in different proportions.

• This causes them to move at different rates through the paper.

Interpreting a chromatogram

Separation by chromatography produces a chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances:

• a pure substance produces one spot on the chromatogram

• an impure substance, or mixture, produces two or more spots

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