Chromatography

• What are the basic principles of chromatography?

  Mixtures being separated if it's dissolved in a solvent and this mobile phase is passed over a solid
• What makes a substance move faster/further through stationary phase?

  • It's more soluble
  • It has an affinity or the mobile phase rather than stationary phase
• How do you calculate the Rf value

  Rf = distance travelled by substance /

  distance travelled by solvent
• What stationary phase is used in TLC?

  • Thin layer of silica
• What can be used to visualise sample spots?

  • UV light
  • Chemical staining
  • Locating agents like ninhydrin or iodine
• Why are Rf values useful?

  They can compare to known literature values that are unique to compounds. Making it more accurate.
• What precautions can be taken during TLC?

  • Plastic gloves - stops stains or fingerprints from interfering
  • Pencil line - it's insoluble
  • Developing tank - allows time for the solvent to rise up the page
  • Fume cupboard - fumes that are removed from plate may be toxic
• What is used as the stationary phase in column chromatography?

  • Powder e.g. silica, aluminium oxide or resin
• Why is mineral wool place in the end of the column in column chromatography?

  So the stationary phase dosnt block the biuret
• What's the advantage of column chromatography?

  Large amounts can be separated at once
• How does column chromatography work?

  1. Stationary phase is packed into the column
  2. Sample is placed at the top
  3. Solvent is continually added in the top and moves through the column via gravity
  4. Creates bands within the column
• What gases could be used as the mobile phase in gas chromatography,

  • Nitrogen
  • Helium
• What can you tell from the graph of gas chromatography?

  • Number of peaks = N of components
  • Height of peak = concentration
  • Position of peaks = Rf value
• How does gas chromatography work?

  1. Happens in a GC machine by an inert carrier gas
  2. The column is packed with a powdered solid which has a thin liquid on its surface
  3. Then inside an oven it's heated so the liquid quickly turns to gas
  4. The longer it takes to pass through the greater the Rf values
• Why is the gas used in gas chromatography inert?

  So it dosnt react with any compounds present in the sample
• How does gas chromatography work? 1. Happens in a GC machine by an inert carrier gas

  2. The column is packed with a powdered solid which has a thin liquid layer on its surface

  3. Then inside an oven it's heated so the liquid quickly turns to gas

  4. The longer it takes to pass through the greater the Rf values
• How does gas chromatography work? 1. Happens in a GC machine by an inert carrier gas

  2. The column is packed with a powdered solid which has a thin liquid layer on its surface

  3. Then inside an oven it's heated so the liquid quickly turns to gas

  4. The longer it takes to pass through the greater the Rf values