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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
- 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
- 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