Lab Report 5_CH 237-016

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Dec 6, 2023

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Patti Smith CH 237-016 TA: Deblina Bhowmick 3/2/23 Experiment 5: Thin Layer Chromatography Analysis of Drug Compounds I. Introduction This lab addresses the composition of various unknown analgesic drugs. There are four standard components to this type of mixture: aspirin, acetaminophen, ibuprofen, and caffeine. Each of these compounds contain unique properties that can provide information about unknown compounds when compared side by side. Through these comparisons, three unknown drugs will be identified per the goal of this experiment. According to the literature, the unknowns may be as follows: Advil (200mg Ibuprofen), Anacin (400mg Aspirin, 32mg Caffeine), Aspirin (325mg Aspirin), Excedrin (250mg Aspirin, 250mg Acetaminophen, 65mg Caffeine), or Tylenol (325mg Acetaminophen). In order to compare the standards to the unknowns and determine which drugs are being tested, a variety of techniques are used. A small spot of each solution (three unknowns and the four standards) is added in its own section to the starting line of a silica gel thin layer chromatography (TLC) plate with a fluorescent indicator. The TLC plate is developed in 200:1 ethylacetate/acetic acid and then allowed to dry. Once dry, short-wavelength (254nm) UV light is used to identify the centers of intensity for each spot. These intensity centers are compared so as to identify each component. Each standard shows a unique spot placement on and the unknowns reflect this with their component(s). II. Results R f (aspirin): 2.4cm/2.9cm = 0.83 R f (acetaminophen): 1.7cm/2.9cm = 0.59 R f (ibuprofen): 2.6cm/2.9cm = 0.90 R f (caffeine): 0.6cm/2.9cm = 0.21 R f (unknown 1) 1 st spot: 0.5cm/2.9cm = 0.17 2 nd spot: 2.1cm/2.9cm = 0.72 R f (unknown 2) 1 st spot: 0.6cm/2.9cm = 0.21 2 nd spot: 1.7cm/2.9cm = 0.59 3 rd spot: 2.1cm/2.9cm = 0.72 R f (unknown 3): 2.5cm/2.9cm = 0.86

III. Discussion A TLC was run in order to identify the presence of various standard active ingredients in three unknown samples. Comparisons are made between the unknowns and standards through the calculated R f values. The R f values and molecular structures communicate a great deal about each standard. It can be assumed that of the four standards caffeine is by far the most polar, followed by acetaminophen, aspirin, and ibuprofen. Compounds that are highly polar are highly retained in the TLC which is shown by a low R f value, such as that of caffeine (0.21). The molecular structure of caffeine contains a good amount of both nitrogen atoms and carboxylate groups, which are more polar than carbon and pull electrons closer through lone pairs. Caffeine is also bicyclic, which can increase polarity. Acetaminophen and aspirin contain a similar number of polar atoms to each other, but less than caffeine, which could explain some of the similarities and differences in polarity. The differences mainly come in the presence of a benzene ring in acetaminophen and aspirin, while there is not one present in caffeine. The lone pairs of nitrogen and electronegative hydroxyl and carbonyl groups of acetaminophen make it more polar than the ester of aspirin. Ibuprofen is much less polar than any of the other standards because it lacks multiple polar functional groups. The observed R f values for the unknown components are not exactly the same as the standards, but they are comparable enough to infer. For example, the first spot of unknown 1 had an R f value of 0.17 which is slightly lower than the caffeine standard (0.21). However, these two values are close enough to each other that it can be assumed that the unknown is caffeine. The discrepancies between the two values are likely due to some spots overlapping during the spotting process as some spots were larger than desired. Overlaps could cause the TLC to appear as if other compounds were in a row that they were not or slightly affect the solutions polarity. Both could result in the TLC being less accurate. Other than the possibility of initial overlap, there were not many noticeable errors as the solvent did not reach the start line and wash away any spots.

IV. Conclusion The R f values for unknown 1 align with aspirin and caffeine at 0.72 and 0.17 as compared to the standards of 0.83 and 0.21. Unknown 2 shows caffeine, acetaminophen, and aspirin at 0.21, 0.59, and 0.72. The standard values for these components are 0.21, 0.59, and 0.83, respectively. Unknown 3 contains one component determined to be aspirin at 0.86 which is slightly higher than the standard of 0.83. From this data it can be determined that unknown 1 is most likely Anacin, unknown 2 is Excedrin, and unknown 3 is Aspirin. Despite not perfectly aligning on the TLC, this interpretation should accurately reflect the identities of the unknowns. V. Additional Questions 1) What would have happened to the Rf values of the 4 components if the TA had accidentally made the solution using diethyl ether instead of ethyl acetate? If the TA had prepared the eluent solution with diethyl ether instead of ethyl acetate, the R f values would likely appear to be much lower than they should. Diethyl ether is less polar than ethyl acetate because it is not an ester. This lower polarity would cause the spots to move less than if they were in the presence of an ester. It is possible that the spots may not move at all if diethyl ether is not polar enough. This could affect the accuracy of the TLC interpretation. 2) Suppose that the generic acetaminophen that we used actually contained phenacetin (see experiment 1 for the structure). Would you expect phenacetin to have a higher or lower Rf value than acetaminophen. Briefly explain your answer. Phenacetin would likely display a slightly higher R f value than acetaminophen if it was set as the acetaminophen standard. This difference is due to small discrepancies in the molecular structures of each compound. Acetaminophen has an alcohol group, but phenacetin contains an ether with an alkyl group attached (this takes the place of the original hydrogen). The alkyl group makes phenacetin slightly less polar than acetaminophen which, in turn, causes it to travel slightly farther and show a higher R f value. 3) Another common pain reliever, Aleve, contains naproxen sodium as the active ingredient. Find and draw the structure for naproxen sodium. The physiological effects of naproxen sodium are very similar to one of the compounds analyzed in this experiment. Which one do you think it is, and how are they structurally related? The structure of naproxen sodium is seen below. It is most similar in physiological effects to ibuprofen. They are somewhat similar in structure as both contain at least one benzene ring. Naproxen contains two while ibuprofen only has one, but both have functional groups in similar spots (across from each other on the ring). These groups are not exactly the same, but they do share similar properties, such as a carboxyl group.

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4) List three common applications for thin layer chromatography. TLC is a highly versatile separation method. It can be used to analyze virtually any substance class, including pesticides, steroids, alkaloids, lipids, nucleotides, glycosides, carbohydrates, and fatty acids. A common application for TLC is the analysis of drug residues and antibiotics in food and environmental samples. It can also be used to identify and quantify colors, ingredients, preservatives, and sweetening agents in food and cosmetic products. Another common use of TLC is in the quality control and purity testing of pharmaceutical formulations.