Part 1: Preparing TLC Plates

photo of the five TLC solutions used in this lab - five labeled 20 mL vials filled with clear liquid and varying amounts of white crystals

The answer to the previous question was Plate 1B. Make sure that the spotting line is approximately 1 cm from the bottom of the plate - otherwise, your spots might be below the solvent line once you put the plate in the chamber.

Now that we've drawn our spotting line, we need to spot the five compounds onto the plate. To do this, dip your spotter into a dilute solution of the compound, then touch the spotting line quickly and lightly. Drain the spotter onto a paper towel between each compound.

A TLC plate is in the foreground, while a paper towel is in the background. A gloved student holds up a vial labeled "BIPHENYL" as well as a thin glass capillary tube to the camera. She dips the capillary into the vial, then quickly touches the capillary to the TLC plate lane labeled "B" several times. She drains the capillary onto the paper towel, then repeats the process with a vial labeled "CAFFEINE."

Before you develop a TLC plate, you should look at the plate under a UV lamp to make sure you have loaded enough sample onto the plate (but not too much!). Here are three different possible TLC plates, visualized under a UV lamp prior to developing.

Plate 1C

Plate 1D

Plate 1E

Which TLC plate do you think you should develop: Plate 1C, Plate 1D, or Plate 1E?

Plate 1C

Plate 1D

Plate 1E

Previous Page: Drawing your Spotting Line

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