Chromatography

• What is chromatography?

  Chromatography is an analytical technique that separates components in a mixture.
• What are the two phases involved in chromatography?

  The two phases are the mobile phase and the stationary phase.
• What can the mobile phase be in chromatography?

  The mobile phase may be a liquid or a gas.
• What can the stationary phase be in chromatography?

  The stationary phase may be a solid or a liquid on a solid support.
• How does a solid stationary phase separate components?

  A solid stationary phase separates by adsorption.
• How does a liquid stationary phase separate components?

  A liquid stationary phase separates by relative solubility.
• What happens if the stationary phase is polar and the mobile phase is non-polar?

  Non-polar compounds would pass through the column more quickly than polar compounds.
• What does separation by column chromatography depend on?

  Separation depends on the balance between solubility in the moving phase and retention in the stationary phase.
• What is the mobile phase in gas-liquid chromatography (GC)?

  The mobile phase is an inert gas such as nitrogen, helium, or argon.
• What is the stationary phase in gas-liquid chromatography (GC)?

  The stationary phase is a liquid on an inert solid.
• What are the types of chromatography?

  • Thin-layer chromatography (TLC)
  • Column chromatography (CC)
  • Gas chromatography (GC)
• What are the steps in the method for thin-layer chromatography (TLC)?

  1. Draw a pencil line on the TLC plate.
  2. Add a tiny drop of each solution to the plate.
  3. Add solvent to a chamber.
  4. Place the TLC plate in the chamber.
  5. Mark the solvent level when it reaches near the top.
  6. Dry the plate in a fume cupboard.
  7. Use a UV lamp to visualize the spots.
  8. Calculate the Rf values.
• What is the purpose of retention times and Rf values in chromatography?

  Retention times and Rf values are used to identify different substances.
• Why should gloves be worn during TLC?

  To prevent contamination from hands to the plate.
• Why is a pencil line used in TLC?

  A pencil line will not dissolve in the solvent.
• What happens if a drop is too big in TLC?

  A drop that is too big will cause different spots to merge.
• What is the effect of having the solvent too deep in TLC?

  If the solvent is too deep, it will dissolve the sample spots from the plate.
• What is the purpose of the lid in the TLC chamber?

  The lid is used to prevent evaporation of toxic solvent.
• Why should the TLC plate dry in a fume cupboard?

  Because the solvent is toxic.
• What is the purpose of using a UV lamp in TLC?

  A UV lamp is used if the spots are colorless and not visible.
• What is two directional chromatography?

  It is chromatography with two different solvents to separate complex mixtures.
• Why might two directional chromatography be necessary?

  It may be necessary if components in the mixture have the same Rf value or are not soluble in the first solvent.
• What does HPLC stand for?

  HPLC stands for high performance liquid chromatography.
• What is the stationary phase in HPLC?

  The stationary phase in HPLC is a solid silica.
• What is the mobile phase in HPLC?

  The mobile phase in HPLC is a liquid.
• What are the steps in simple column chromatography?

  1. Fill a glass tube with stationary phase (silica or alumina).
  2. Use a filter to retain the solid in the tube.
  3. Add solvent to cover the powder.
  4. Dissolve the mixture in a minimum of solvent and add to the column.
  5. Run a solvent or mixture of solvents through the column.
  6. Record the retention time for each component.
• What is the purpose of gas-liquid chromatography?

  Gas-liquid chromatography is used to separate mixtures of volatile liquids.
• What is the mobile phase in gas-liquid chromatography?

  The mobile phase is an inert gas such as helium.
• What is the stationary phase in gas-liquid chromatography?

  The stationary phase is a high boiling point liquid absorbed onto a solid.
• What is retention time in gas-liquid chromatography?

  Retention time is the time taken for a compound to travel from injection to the detector.
• How can retention times be used in gas-liquid chromatography?

  Retention times can be used to identify a substance.
• What does the area under each peak in gas-liquid chromatography represent?

  The area under each peak is proportional to the abundance of that component.
• What is GC-MS?

  GC-MS is a combination of gas chromatography and mass spectrometry.
• What are some applications of GC-MS?

  GC-MS is used in analysis, forensics, environmental analysis, airport security, and space probes.
• What factors can change the retention times in gas-liquid chromatography?

  Retention times can be changed by GC column temperature, column length, and flow rate.
• What happens if the temperature or flow rate is higher in gas-liquid chromatography?

  If the temperature or flow rate is higher, substances will move more quickly through the column.
• Why is it important to use an inert carrier gas in gas-liquid chromatography?

  An inert carrier gas will not react with the components being separated.