Chromatography: Amino Acids (AQA AS Biology): Revision Note

Chromatography: amino acids

• Chromatography separates a mixture into its components based on their solubility.

• It involves two phases:

  • Mobile phase – moves through the system

  • Stationary phase – does not move

• As the mobile phase passes over the stationary phase, components separate

• Components that are more soluble in the mobile phase travel further, as they spend more time moving and less time bound to the stationary phase

• Paper chromatography can be used in school laboratories to separate a mixture of amino acids

Using chromatography to separate a mixture of amino acids

Method

1. A spot of the unknown amino acid sample mixture is placed on a line at the bottom of the chromatography paper

2. Spots of known standard solutions of different amino acids are then placed on the line beside the unknown sample spot

3. The chromatography paper is then suspended in a solvent

   • Each amino acid will be more or less soluble in the mobile phase than others and will therefore separate, travelling with the solvent at different times/distances from the line, depending on their:

     • charge

     • size

Identification of amino acids

• The unknown amino acid(s) can then be identified by comparing and matching them with the chromatograms of the known standard solutions of different amino acids

  • If a spot from the amino acid mixture travels the same distance as a spot from a known standard, it indicates that the mixture contains that amino acid

• To view the spots from the different amino acids, it may be necessary to first dry the chromatography paper and then spray it with ninhydrin solution; this chemical reacts with amino acids, producing an easily visible blue-violet colour