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
    
    
    • 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

Copyright © 1997-2005 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/matter/chromatography.shtml