chromatography

• TLC phases

  SP - solid silica on a plastic or glass plate

  MP - liquid solvent eg. water or organic
• Column chromatography phases

  SP - solid silica

  MP - liquid solvent eg. water or organic
• gas-liquid chromatography phases

  SP - microscopic liquid film on a solid support

  MP - inert carrier gas eg. nitrogen
• Rf value

  Distance travelled by substance / distance travelled by solvent
• TLC stationary phase

  -thin metal sheet coated in alumina or silica

  -solute molecules absorb onto the surface

  -depending on strength of interactions with SP - different distances travelled

  -more interaction - more they stick - less they move
• TLC mobile phase

  -flows over the stationary phase

  -polar or non polar liquid solvent

  -polar - water or alcohol

  -non polar - alkanes
• to locate spots (TLC)

  -UV light

  -ninhydrin (carcinogenic)

  Iodine vapour
• column chromatography

  -inert solid (powdered silica or alumina) is stationary phase which is placed into the column

  -liquid solvent is mobile phase added to column

  -sample mixture dissolved in the solvent and added to the top of column

  -more solvent is added on top of sample

  -as solvent runs through more is added to prevent drying out

  -component with greatest attraction to stationary phase takes longer to flow through
• gas chromatography

  -used for analysing gases, volatile liquids, solids in their vapour form

  -sample injected into column through self-sealing disc and vapour formed is carried through stationary phase using the inert gas mobile phase
• gas chrom. stationary phase

  -non-volatile liquid

  -method usually uses a long coiled column for the stationary phase
• gas chromo. mobile phase

  -inert carrier eg. helium, nitrogen moves the sample molecules through stationary phase
• retention times (GC)

  -retention time depends on attraction between solute and stationary phase as well as volatility and nature of solute

  -recorded on chromatogram

  -each peak represents volatile compound in sample

  -sizes of peaks related to how much of each compound is present in the mixture
• interpreting GC

  -less polar components travel further up TLC plate - Rf values are higher - more soluble