Chromatography

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Chromatography
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• A means of separating one type of molecule from
  another
• Involves a solution of molecules, a solvent and
  chromatography paper

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Instructions

• Test solution is spotted onto paper using a
  dropper/micropipette (origin)
• You must make several applications of your test
  solution, allowing each to dry in between
  applications, in order to build up a concentrated
  spot

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• Solvent is placed in a suitable container and the
  paper dipped into the solvent below the origin
• Leave for sufficient time for the solvent to move
  up the paper

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front

• Molecules dissolve in the solvent to different
  degrees (molecules have differing solubilities in
  different solutions).
• Movement also depends on how easily molecules are
  absorbed by the paper

Origin
Solvent
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• Most soluble molecules move furthest
• Origin
• Solvent
• (this example shows the pigments found in ink)

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Identification of molecules there are two options

• Run the unknown solution next to a known
  solution. The same molecules will always appear
  at the same position under the same conditions
• Calculate the Rf value

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calculate Rf value

• Rf distance travelled by spot
• distance travelled by solvent
  front
• Rf is always less than 1.0
• Use tables of Rf values to identify molecules