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Jalen Volz Jan 28, 2018 CHEM 243A –Section 7 Hannah Goodman TLC Analysis of Analgesic drugs In the experiment we were given one Tylenol, an aspirin and a Motrin pill. To find out what each drug contains, we found out the Rf values of the pills, and then compared those to the Rf values of the known drugs (Acetaminophen, Acetylsalicylic Acid, Caffeine and Ibuprofen). For the Tylenol pill, the Rf value was around .68. This matched most closely with the Rf value of Acetaminophen which I found to be .65. For the aspirin the Rf value was .8 and that was closest to the Acetylsalicylic Acid which was .75. The last pill, Motrin had an Rf of .97 which was closest to Ibuprofen at .942. None of our pills had caffeine as the active ingredient.  The eluent used in this experiment was ethyl acetate containing 0.5% acetic acid. This choice of solvent with the acetic acid was helpful in displaying better spots with more separation. A solvent without the acetic acid would have left tails on the molecules. Because of the eluents polarity it gave better separation to each molecule. The less polar molecules, Ibuprofen and Acetylsalicylic Acid both went further up the TLC plates because of their low polarities. While Acetaminophen and Caffeine molecules stayed closer to the baseline because they had higher polarities.  The structure of each of these compounds had an effect on the Rf values. All three compounds contained at least one functional group. Ibuprofen only contains one functional group, carboxylic acid. Carboxylic acid is polar, but there is also a benzene ring and other nonpolar groups attached to it, which results in it having the highest Rf value. Acetylsalicylic Acid had the next highest Rf value, meaning it was slightly more polar than Ibuprofen. It also contains a carboxylic acid group with a benzene ring which lowers its polarity. Acetaminophen was the next highest Rf, and it is only less polar than the caffeine because it also contains the benzene ring. It is still more polar than Acetylsalicylic Acid and Ibuprofen because the Nitrogen atoms contain lone pairs. Caffeine had the lowest Rf value, meaning it is the most polar out of the drugs we used. Caffeine contains many electronegative elements. Another way we can use the structure to rationalize the Rf values is by looking at the attractive forces. In caffeine there are Dipole-Dipole interactions and London dispersion forces. In the other drugs, there will be hydrogen bonding with the Silica Gel on the TLC plates. This will play a part in how far up the plate each drug travels. 


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