Learning Objective: Thin Layer Chromatography (TLC) is a form of chromatography in which components of a liquid mixture are separated by means of a thin layer of adsorbent material coated on a glass or plastic sheet. In this procedure you will learn how to use the equipment involved in TLC.

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Students may wish to wear gloves when working with chemicals.

In this experiment you will be using fluorene, fluorenone, ligroin tert-butylmethyl ether, and tert-butylmethyl ether. Fluorene is white, which gives a colorless solution when dissolved in a solvent. Fluorenone is yellow, which gives a yellow solution when dissolved in a solvent. Fluorene and fluorenone have very different polarities that we will take advantage of when we separate the components of a fluorene-fluorenone mixture.

The following equipment is needed for TLC: a TLC chamber, pre-cut filter paper, a TLC plate, a pipet, tweezers, capillary pipettes, and a UV light. When examining the products by TLC, you will need to use a UV light to visualize the colorless fluorene.

   
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The TLC chamber is a jar with a screw-top lid. Put a filter paper liner in the chamber, flat against the sides. Then transfer the developing solvent ligroin tert-butylmethyl ether to the chamber. The final depth of the solvent should be shallow, less than 1 cm. Screw on the lid and shake vigorously so the liner paper is completely saturated.

   
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Prepare the solids for analysis by placing 40 mg of fluorene in one vial and 40 mg of fluorenone in a second vial. Add a small amount (about 2 mL) of tert-butylmethyl ether solution to each vial, cap and shake vigorously. Then set aside while preparing the TLC plate.

   
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Our TLC plates are pre-cut. They are coated with silica gel and have a fluorescent indicator, which allows you to visualize a colorless compound under UV light. Do not touch the face of the plate with your fingers. About 1 cm from the bottom, use a pencil to mark the plate: two dots for the starting points and an "E" underneath one, for example, to identify fluorene. Using a separate capillary for each, spot the plate with the two substances. Spot each three times.

   
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Place the TLC plate in the chamber. Make sure the face of the plate is visible and oriented vertically. Be sure the filter paper does not touch the plate and that the level of the developing solvent is below the starting spots. Watch the solvent climb the face of the plate by capillary action. Remove the TLC plate from the chamber when the solvent approaches the top of the plate (about 3 or 4 minutes). Don't let the solvent front go to the top of the plate or you will have to begin again. Get down and look at eye level as you don't want to shake the TLC chamber.

   
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Remove the plate from the chamber and mark the position of the solvent front. Dry the plate and then analyze it under UV light by shining it on the face of the plate. Circle each spot. Note that fluorene and fluorenone travel different distances on the face of the plate. Your plate needs to be checked by your TA to ensure you're performing the technique properly. Store your plates in a sandwich bag and staple the bag to your post-lab assignment.



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