• 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

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

   

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