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Thin Layer Chromatography Essay

Using the Thin Layer Chromatography experiment, caffeine was found to be the most polar due to the fact that it stayed closer to the stationary phase. Caffeine contains four amine groups that are extremely polar as a result of the hydrogen bond and amide functional group. Acetaminophen was found to be the second most polar analgesic drug tested. Acetaminophen contains a polar alcohol group on one side and amide group on the other but also includes non-polar functional groups that consisted of the benzene ring and methyl group. Acetylsalicylic acid low polarity results from only containing a carboxylic acid and ester and the presence of alkenes in the benzene ring. Ibuprofen was the least polar out of all analgesic drugs because it only contains one carboxylic acid and non-polar functional groups.

The behavior of these compounds in function of their structure and polarity were inversely associated. The TLC plate is made up of highly polar silica gel. Caffeine showed the smallest Rf value of (.278), shadowed by acetaminophen Rf value of .5556 cm, followed by acetylsalicylic acid’s Rf value of (.667), and then the largest Rf value that ibuprofen had of (.722). The polar molecules of the analgesic drugs were attracted to the highly polar silica gel, which explains the low retention rate of caffeine that and the high retention rate of the ibuprofen that is the least non-polar.

The eluent used for this experiment was a 50:50 mixture of ethanol and methyl chloride due to both liquids polarity. Caffeine and acetaminophen are very polar and the table itself is extremely polar so therefore needs an eluent that is reasonably polar or the experiment would not have the same result. The substances would not be able to move up the plate if the eluent was not as polar as the silica gel because of the abundant attraction to the plate. For this purpose, ethanol and methyl chloride were chosen. The mixture had to be a 50:50 because if the liquids were unequally mixed it would result into smaller Rf values and would become difficult to distinguish the different substances.

After performing this experiment and calculating Rf values, the same procedure was used to identify the ingredients in over the counter analgesics. The five over the counter analgesics extracted for testing were Tylenol, Excedrin, Motrin, Bayer, and a mixed solution. Following the procedure the Rf values calculated resulted in Tylenol with one Rf value of (.613). Comparing Tylenol’s Rf value with the Rf values from the first plate it can be that it can be concluded that it contains acetaminophen. Excedrin was composed of three Rf values of (.288), (.563), and (.688), based on those Rf values Excedrin must have caffeine, acetaminophen, and ibuprofen. Motrin traveled the farthest up the plate and showed a Rf value of (.763). Since it traveled the highest up the plate Motrin is the least polar and corresponds to Ibuprofen’s polarity and Rf value. Bayer displayed one Rf value of (.688) and based on that calculation Bayer contains Acetylsalicylic acid. Looking at the mixed solutions it is easily determined which solution is what based on their Rf values and behaviors. This experiment was successful because it was easy to determine what substances were what or what they contained based on their functional groups and how they would behave, and comparing calculated Rf values.


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