Thin-Layer Chromatographic Analysis of Drug Components

Experiment Objective:
To identify the components of an analgesic drug tablet and then correctly identify the tablet from a group of others with acquired data.

Experiment Summary:
In this experiment, we use TLC to identify components of an unknown analgesic drug. We prepare a solution of the drug by dissolving part of a tablet in 1:1 ethanol/dichloromethane, then spotting a TLC plate with the solution along with standard solutions of all active substances the drug tablet is likely to contain. Once the TLC plate develops and dries, it is viewed under ultraviolet light to properly visualize and mark the greatest intensity of spotting.

Experiment Data:

Rf Value = distance from baseline travelled by solute/distance from baseline travelled by solvent Unknown =

Trial 1:
Rf1 Unknown 5.1cm/7.4cm = .689
Rf1 Unknown 5.0cm/7.4cm = .676
Rf2 Aspirin 5.0cm/7.4cm = .676
Rf3 Acetaminophen 2.9cm/7.4cm = .392
Rf4 Ibuprofen 2.9cm/7.4cm = .392
Rf5 Salicylamide 5.0cm/7.4cm = .676
Rf6 Caffeine 1.0cm/7.4cm = .135

Trial 2:
Rf1 Unknown 5.0cm/7.4cm = .676
Rf1 Unknown 5.0cm/7.4cm = .676
Rf2 Aspirin 5.2cm/7.4cm = .703
Rf3 Acetaminophen 3.3cm/7.4cm = .446
Rf4 Ibuprofen 4.9cm/7.4cm = .662
Rf5 Salicylamide 5.1cm/7.4cm = .689
Rf6 Caffeine 0.9cm/7.4cm = .122

Observations, Results, & Discussion:
After performing the experiment twice to improve the accuracy of our findings, we were still left somewhat unsure with our outcome. After computing the Rf values for each of our trials, our final calculations did not leave us with clear cut and easily discernable results. Overall, between the two separate trials, we spotted and calculated our knowns twice each, and our unknown 4 times total, in 2 different concentrations. The column for our unknown contained only 1 solid and pronounced mark, which was measured most consistently at Rf = .676 which matched our calculations for Aspirin and Salicylamide. Immediately we can rule out a couple possible compositional elements. Acetaminophen measured at .392 and .446 so Tylenol and Excedrin were excluded.

Caffeine alone measured at .135 and .122, and not once did we see the slightest mark for caffeine in our unknown column. We felt it could not be entirely ruled out as a component to our unknown because it is only an ingredient in such miniscule concentrations that the possibility for it to not leave an easily viewable mark would be too great. Our results for Ibuprofen testing produced 2 very different numbers, .392 and .662. Overall, we felt it was reasonable to eliminate this in our unknown since it is only apparent in Advil and would have shown a lower marking in our unknown column. But ultimately, by logical deduction we narrowed down our unknown to one of 2 possible drugs; if we did make an error in plate reading and our caffeine concentration was not fully visible, then there is a possibility for our unknown to have been B.C. Tablets.

In the end, with our markings considered fully correct, the final determination of our unknown was Aspirin, primarily due to the lack of any other ingredient present. As with any experiment, there is always the possibility for an error to occur that can damage the data collected and skew the results. During our first trial we ran into some issues with the clarity of spotting on our plates, causing difficulty marking, which led us to restarting our investigation. A step we may have made a mistake during was the application of the known and unknowns to the plate. We may have over-blotted, not allowed our application to fully dry between additional blots, placed our blots to low and entirely submerged them in the developing solution. All of these errors would have affected our data, but ideally performing the experiment twice gave us a more reliable set of results.