chromatography Flashcards
what are the three types of chromatography
thin layer chromatography - plate coated in solid and solvent moves up
column chromatography - column packed with solid and solvent moves down column
gas chromatography - column packed with solid and gas is passed through under pressure at high temperature
separation depends on
the balance between solubility in moving phase and retention by stationary phase
what is a stationary phase and what is a mobile phase
stationary is solid substance which the mixture passes over in order to be separated
mobile phase is either the liquid or gas which carries over the solid material
high affinity to stationary phase means
it will travel more slowly
if mixture is highly soluble in mobile phase it will
travel more quickly with the solvent
in thin layer chromatography what is the stationary and mobile phases
stationary - silica gel which coats the glass
mobile phase - solvent
rf values
distance moved by component over the distance moved by the solvent front
advantages of TLC
limitations of TLC
advantages -
- faster than paper chromatography
- will work on small samples
- can be used to determine when a chemical reaction is complete
limitations -
- similar compounds have similar rf values
- conditions must be kept the same in order to fairly compare rf values
- new compounds have no reference
- cannot be used on large quantities
column chromatography
like a burette
column packed with powder such as silica which is the stationary phase
mixture to be separated is added
solvent is added and soaks down stationary phase
this is the mobile phase
diff compounds travel down and can be collected at different times
advantage of column chromatography
larger quantities can be separated
mobile phase in gas chromatography
stationary phase
gas which is unreactive such as nitrogen or helium
high molecular mass alkane with high boiling point
retention time
the time it takes from the point of injection for the component to the detector
limitations of gc
unknown compounds have no reference retention times
many have similar retention times peak shapes and detector responses
