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. The compounds that contain a carboxylic acid group would be expected to be more polar and have a lower Rf value. After doing the experiment, the two compounds with the carboxylic acid group are the two with the highest Rf values. Both Acetylsalicylic Acid and Ibuprofen have a carboxylic group which participates in hydrogen bonding when eluted on the TLC plate of Silica Gel. The hydrogen bonds causes the molecules to move further up along the plate than both Acetaminophen and Caffeine because of the attractive forces with the stationary phase of the Silica Gel.