Chromatography

• What is chromatography?

  Analytic technique for separating mixtures
• Describe the three types of chromatography

  TLC

  • thin-layer chromatography
  • separates solids

  CC

  • column chromatography
  • separates liquids

  GC

  • gas chromatography
  • separates gases
• Describe how chromatography works

  Stationary phase

  • POLAR
  • Greater affinity to polar molecules
  • TLC spots don't move much
  • CC/GC retention times are long

  Mobile phase

  • NON-POLAR
  • Greater affinity to non-polar molecules
  • TLC spots move a lot
  • CC/GC retention times are short
• Why does an alkene have a shorter retention time than an alcohol?

  The alkene is less polar than the alcohol

  And so has a greater affinity to the mobile phase
• What is the point of using a lid in TLC?

  Stops solvent from evaporating at the end of the TLC plate
• What is the equation to calculate Rf?

  Distance travelled by spot / distance travelled by solvent
• What does a large Rf indicate?

  Non-polar sample
• What does a small Rf indicate?

  Polar sample
• How are species identified in chromatography?

  Compare Rf value to a data bank and find species

  Compare with samples I suspect are in the unknown
• How are invisible spots identified?

  Dying spots:

  • Ninhydrin for amino acids
  • Iodine

  Highlighting spots:

  • Use UV light