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What is chromatography?

  • chromatography is a versatile technique for separating mixtures
  • strategy: flow the mixture over a material that retains some components more than others, so different components flow over the material at different speeds
    • a simple analogy for chromatography
      If you don't see the animation above, a nonanimated version is available; or you can download the free Flash plugin from Macromedia.

    • mixed swarm of bees and wasps swept by the wind over a flower bed...
    • bees visit flowers; wasps stay airborne
    • wasps leave the bed first; swarm separated on the basis of affinity for flowers
  • in chromatography, a mobile phase sweeps the sample over a stationary phase (as the wind sweeps the swarm over the flower bed)

Advantages of chromatography

  • can separate very complex mixtures
    • drugs, plastics, flavorings, foods, pesticides, tissue extracts, fuels, air samples, water samples, ...
  • very small sample sizes
  • separated components can be collected individually
  • analyses can be highly accurate and precise

Sheet chromatography

  • paper chromatography (PC)
    • stationary phase is liquid soaked into a sheet or strip of paper
    • mobile phase is a liquid solvent
    • some components spend more time in the stationary phase than others
    • components appear as separate spots spread out on the paper after drying or "developing"
  • thin layer chromatography (TLC)
    • stationary phase is a thin layer of adsorbent (Al2O3 or SiO2, usually) coating a sheet of plastic or glass
    • some components bond to the adsorbent strongly; others, more weakly
    • as with paper chromatography, components appear as spots on the sheet

Column chromatography

  • gas chromatography (GC)
    • sample mixture is injected into a long tube (the column)
    • mobile phase is an inert gas that sweeps the sample down the tube
    • stationary phase lining the tube selectively adsorbs or dissolves components
      • the stationary phase is a solid or very syrupy liquid
      • silicone polymers (like Silly Putty!) are often used as stationary phases in gas chromatography
    • a detector responds to separated components as they leave the tube

What is chromatography used for?

  • finding concentrations
    • gas chromatogram of gasoline
    • ion chromatogram of orange juice
      ion chromatogram of orange juice
      • each peak corresponds to a separate component in the mixture
      • area of each peak is proportional to concentration
  • chemical fingerprinting
    • species identification
      • "killer" bees can be distinguished from native bees by comparing gas chromatograms of cuticle extracts
    • tracing contraband sources
    • detecting drugs in urine
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General Chemistry Online! Chromatography

Copyright © 1997-2005 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 07/25/05.URL: http://antoine.frostburg.edu/chem/senese/101/matter/chromatography.shtml