6.6 - Chromatography Flashcards
What is chromatography used for?
to separate individual components from a mixture of substances
e.g analysis of drugs, plastics, flavourings, air samples
What is the stationary phase?
doesn’t move (usually solid/liquid supported on solid)
- greater affinity to this: moves shorter distance and/or slower
What is the mobile phase?
moves (usually liquid/gas)
- more soluble in this: moves further and/or faster
Describe how to carry out TLC
- draw baseline with pencil on TLC plate
- spot small amount of solution on line with capillary tube
- pour solvent in beaker to depth below base line and add TLC plate, covering with watch glass on top
- leave solvent to rise until 1cm from top
- remove plate and mark solvent front with pencil
- allow plate to dry, then draw circles around visible spots
- calculate retention factor = distance moved by component/solvent
What are the benefits of TLC?
- quick
- inexpensive
- indicates no. components in mixture
How is separation achieved in TLC?
different components have different affinities for adsorbent and bind w/ different strength to surface
Describe how gas chromatography works
- small amount of mixture injected into column and carried by mobile phase (inert carrier gas e.g He)
- slows down as interacts with liquid stationary phase
- more soluble in stationary phase = moves more slowly through tube so larger retention time
- more soluble in mobile phase = moves faster so smaller retention time
- each component produces a peak on gas chromatogram
- compare to known values to determine concs
What is gas chromatography used for?
to separate/identify volatile organic compounds
Describe how to interpret a gas chromatogram
relative peak size: how much of each compound present in mixture
- to identify unknown molecules, compare Rf with data book
