Question

List six problems in doing thin layer chromatography. Explain what happens in each of the problems, and say how these problems can be fixed.

Answer 1

1. In preparing TLC plate : It is a very deficult task to prepare a TLC plate because the solvent of silica gel, if the quanytity of water is increases it get  fallen off from the sides of the glass plate. So make sure the quantity of water in it shoud be proper.

2. The sample runs as a smear or rising upward : Compounds which possess strongly acidic or basic groups (amines or carboxylic acids) sometimes show up on a TLC plate with this behavior. Add a few drops of ammonium hydroxide (amines) or acetic acid (carboxylic acids) to the eluting solvent to obtain clearer plates.

3. The sample runs as a downward crescent: Likely, the adsorbent was disturbed during the spotting, causing the crescent shape.

4. Many random spots are seen on the plate: Make sure that you do not accidentally drop any organic compound on the plate. If get a TLC plate and leave it laying on your workbench as you do the experiment, you might drop or splash an organic compound on the plate.

5. You see a blur of blue spots on the plate as it develops: Perhaps you used an ink pen instead of a pencil to mark the origin you will see different blue spots so make sure use pencil to makr spots.

6. No Spots Seen on the Plate: The concentration/quantity of the sample is too low. You can overcome this problem by spotting the sample multiple times in the same place on the slide (allowing the solvent to dry in between applications). Or the development method needs to be changed.