AQA A Level Chemistry

Revision Notes

7.11.3 Column Chromatography

Column Chromatography

Column Chromatography

  • In column chromatography, the column is often a long vertical glass tube or in the laboratory a burette is suitable
  • An inert solid (usually powdered silica gel or alumina) is the stationary phase which is placed in the column
  • A liquid solvent phase, mobile phase, is added into the column until it is saturated with solvent
    • Care should be taken when setting up the column because cracks in the stationary phase can lead to issues during separation
  • The sample mixture is dissolved in the solvent and introduced at the top of the column
    • A pipette is usually used to carefully add the dissolved sample to the top of the column
    • The aim here is to add the sample without disturbing the surface of the column so that the sample runs from one level through the column
  • Once the sample has been added, more solvent (eluent) is added on top of the sample
  • As the solvent runs through, fresh solvent is added to the top of the column so that it does not dry out
  • The sample flows through the column via gravity
    • This process can be sped up by pushing the sample and mobile phase through the column
    • In school laboratories, this can be achieved by attaching a gas syringe to the top of the chromatography column
    • In industrial / research laboratories, this is achieved by attaching an air line to the top of the chromatography column
  • The component with the greatest attraction / affinity to the stationary phase takes the longest time to flow through the column
  • If the components are coloured, then they can be identified using the Rf value
  • If the components are colourless, then other techniques such as fluorescence under UV light can be used to show their position in the column

Column chromatography, downloadable AS & A Level Chemistry revision notes

Column chromatography showing the separation of coloured compounds in a glass burette

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