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How to Identify Carbonyl Compounds in Orange Peels by Thin Layer Chromatography

Thin layer chromatography (TLC) is a method of determining the identity and quantity of unknown substances in a mixture. It is based on the principle that each substance has a unique molecular weight and size which determines the distance that it travels via capillary action through a stationary phase. In the case of TLC, the stationary phase is a thin, absorbent layer, applied to a glass, metal or plastic plate. A solution of many compounds - such as prepared orange peel solution - can be separated to reveal each component using this method.

Things You'll Need

  • Thin layer chromatography plate
  • Large beaker
  • Tin foil
  • Micropipettes
  • Ruler
  • Pencil
  • Lab notebook
  • Orange peel solution
  • Solutions of individual carbonyl compounds
  • Developing solution
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Instructions

  1. Performing Thin Layer Chromatography

    • 1
      Make the line visible but be careful not to press too hard as this can pierce the TLC plate.

      Draw a straight line about 1 cm above the base of the TLC plate using the pencil and ruler.

    • 2
      Leave enough space between zones to ensure that the samples do not mix.

      Mark "spot zones" along this line with a pencil. Ensure that there is at least 1 cm of space between each spot zone.

    • 3

      Number the spot zones on the TLC plate with a pencil. Place the numbers underneath the pencil line. This prevents sample contamination.

    • 4
      Check on the plate often to prevent over drying.

      Dry the plate in an oven preheated to 50 degrees Celsius for up to 20 minutes.

    • 5
      It may be helpful to create a diagram of the TLC plate and the position of all the solutions for future consultation.

      Use micropipettes to apply small samples of the orange peel solution and different known carbonyl solutions to the spot zones. Apply each solution with a new, clean, dry micropipette to avoid contamination. Apply a different solution in each spot zone. Carefully draw and label each application in a lab notebook.

      For example, zone 1 = methanal, zone 2 = orange peel solution, zone 3 = propanal.

    • 6

      Allow the spot solutions to dry.

    • 7
      To ensure a tight seal, curl the edges of the foil cover under the lip of the beaker.

      Pour developing solution into a large beaker until the solution is 5mm deep. Place a tight tin foil cover over the beaker to prevent the developing solution from evaporating.

    • 8
      Be very careful when inserting the TLC plate.

      Gently place the TLC plate in the beaker, touching only the edges of the plate. Re-cover the beaker with the tin foil cap and let the plate develop.

    • 9
      Since many developing solutions are harmful, dry the plate in a closed fume hood.

      Remove the TLC plate when the line of developing solution is approximately 1 cm from the top of the plate. Mark this line with the pencil and ruler. Let the TLC plate dry.

    • 10
      Keep the original plate because you may have to hand it in with your lab report.

      Reveal the spots on the TLC plate by passing the plate under UV light or placing it in a chamber with a few iodine crystals. Lightly outline each spot with a pencil. Draw a second diagram of the plate in your notebook, noting the size and location of each spot.

    Identifying Compounds on a TLC Plate

    • 11
      If you can, estimate the distance to two decimal points.

      Measure from the bottom pencil line to the center of each spot with the ruler. Record the distance each spot has traveled In your lab notebook.

    • 12

      Measure the distance between the pencil lines. Record this measurement in your lab notebook.

    • 13
      Each spot should have its own Rf value.

      Calculate the Rf value for a spot by dividing the distance the spot traveled by the distance between the two pencil lines.

    • 14

      Compare the Rf values of the orange peel spots to the known carbonyl spots. The spots that have the same Rf values are matches.

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