AQA A Level Biology

Revision Notes

1.1.6 Chromatography: Monosaccharides

Chromatography: Monosaccharides

  • Chromatography is a technique that can be used to separate a mixture into its individual components
  • Chromatography relies on differences in the solubility of the different chemicals (called ‘solutes’) within a mixture
  • All chromatography techniques use two phases:
    • The mobile phase
    • The stationary phase
  • The components in the mixture separate as the mobile phase travels over the stationary phase
  • Differences in the solubility of each component in the mobile phase which affects how far each component can travel
  • Those components with higher solubility will travel further than the others
  • This is because they spend more time in the mobile phase and are thus carried further up the paper than the less soluble components

Paper Chromatography

  • Paper chromatography is one specific form of chromatography
  • In paper chromatography:
    • The mobile phase is the solvent in which the sample molecules can move, which in paper chromatography is a liquid e.g. water or ethanol
    • The stationary phase in paper chromatography is the chromatography paper

Paper chromatography method

  • A spot of the mixture (that you want to separate) is placed on chromatography paper and left to dry
  • The chromatography paper is then suspended in a solvent
  • As the solvent travels up through the chromatography paper, the different components within the mixture begin to move up the paper at different speeds
    • Larger molecules move slower than smaller ones
    • This causes the original mixture to separate out into different spots or bands on the chromatography paper
  • This produces what is known as a chromatogram

Chromatogram example, downloadable AS & A Level Biology revision notes

An example of a chromatogram that has been produced by using paper chromatography to separate a spot of ink

Using chromatography to separate a mixture of Monosaccharides

  • Paper chromatography can be used to separate a mixture of monosaccharides
  • Mixtures containing coloured molecules, such as ink or chlorophyll, do not have to be stained as they are already coloured
  • Mixtures of colourless molecules, such as a mixture of monosaccharides, have to be stained first
  • A spot of the stained monosaccharide sample mixture is placed on a line at the bottom of the chromatography paper
  • Spots of known standard solutions of different monosaccharides are then placed on the line beside the sample spot
  • The chromatography paper is then suspended in a solvent
  • As the solvent travels up through the chromatography paper, the different monosaccharides within the mixture separate out at different distances from the line
  • The unknown monosaccharides can then be identified by comparing and matching them with the chromatograms of the known standard solutions of different monosaccharides
    • If a spot from the monosaccharide sample mixture is at the same distance from the line as a spot from one of the known standard solutions, then the mixture must contain this monosaccharide

Chromatography of monosaccharides (1), downloadable AS & A Level Biology revision notes

Chromatography of monosaccharides (2), downloadable AS & A Level Biology revision notes

Chromatography of monosaccharides (3), downloadable AS & A Level Biology revision notes

How chromatography can be used to separate a mixture of monosaccharides and identify the individual components

Exam Tip

Paper chromatography is the name given to the overall separation technique while a chromatogram is the name given to the visual output of a chromatography run. This is the piece of chromatography paper with the visibly separated components after the run has finished.

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