RP 12 Thin-layer chromatography

• What is the purpose of thin layer chromatography (TLC)?

  To separate a mixture into its constituent components for analysis.
• How does TLC allow for identification of components?

  By the calculation and comparison of Rf values.
• What is the formula to calculate an Rf value?

  Rf value = Distance travelled by component ÷ Distance travelled by solvent
• What are the steps to carry out thin layer chromatography (TLC)?

  1. Add solvent to a jar and seal it.
  2. Draw a pencil line on the TLC plate and spot samples along this line.
  3. Place the TLC plate in the jar, ensuring the solvent is below the pencil line.
  4. Allow the solvent to rise up the plate, carrying the components with it.
  5. Draw a pencil line where the solvent finishes and allow to dry.
• Why must any lines drawn on the TLC plate be in pencil?

  Because if drawn in ink, it will dissolve in the solvent and contaminate the plate.
• Why should the solvent be below the pencil line on the TLC plate?

  If above the pencil line, the solvent will dissolve all samples and they will not run up the plate.
• What happens if your sample is too concentrated in TLC?

  If your sample is too concentrated, then the spots overlap.
• What occurs if you use less solvent and have a high baseline in TLC?

  You will get large spots.
• How can you view the spots on a TLC plate?

  • Some spots may be visible, while others may require a UV lamp/light.
  • The plate can be sprayed with a chemical/locating agent to reveal 'invisible' spots.
• What does a diagram of thin-layer chromatography illustrate?

  A visual representation of the TLC process and setup.