TLC Analysis of Analgesic Drugs
In this experiment, thin-layer chromatography (TLC) was used to determine the composition of various over-the-counter (OTC) analgesics: Anacin, Bufferin, Excedrin, and Tylenol. The TLC plates were first viewed under ultraviolet (UV) light and then treated with iodine vapor in order to visualize the spotting.
Experiment Scheme Initially, sixteen capillary micropipets were created in order to spot the TLC plates. Two TLC plates were then obtained and marked with pencil for spotting. A line was drawn 1 cm from the bottom of each plate, and five small, evenly spaced marks were made along those lines (see Figure 1). Each mark indicated where a substance would be spotted.
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Excedrin and Anacin contain aspirin as well, but this was not shown by the data. One problem that arose in this experiment was that the reference plate gave very similar Rf values for aspirin and salicylamide and neither of them turned color after exposure to the iodine. This made it difficult to tell which compound was in Bufferin. Salicylamide and aspirin are similar compounds2, so it would make sense for our tests to show them to have similar properties. The other problem encountered with the results was that aspirin did not spot in Excedrin or Anacin. There were two spots on the top left and right side of the sample plate and some coloration in between. These things were all ignored and considered erroneous because they weren’t in line with the other spots. The two larger spots were in the approximate location of where the plate was handled, so this could be what created those spots. It could be that the aspirin was in the coloring between the two spots. If too much of the sample was applied, it could cause the aspirin to tail and not create defined spots. It could also be that too little sample was applied and no spots were created for the aspirin. The problem of not applying the correct amount of solvent could be resolved by using better capillary micropipets. The ones used in this experiment were crudely made, and it was difficult to judge exactly how much sample had been applied. It would have been