Experiment 5 - lab report 2019 PDF

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lab report 2019...

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1 Tiffany Rutledge CH 237-021 Lisa Fealy 11 March 2020

TLC Analysis of Drug Mixtures Introduction: The goal of this experiment is to determine the contents of three separate unknown drug mixtures by utilizing thin layer chromatography to compare the three unknown drug components with four known components—aspirin, acetaminophen, ibuprofen, and caffeine. The problem in this experiment is that there are multiple possible identities for the three unknown components, so thin layer chromatography will be used to obtain and compare RF values of the unknown to those of the four known compounds. In order to conduct this experiment, the three unknown samples and the four known samples were obtained and both run on TLC plates. UV light was utilized to determine the distance each compound had traveled from the baseline. The Rf values were then calculated for the unknown and were then compared with the known in order to determine the composition of each unknown sample.

2 Results: Known Rf Values -

Distance from solvent front: 3.5 cm Compound Aspirin

Distance Traveled 2.7 cm

Acetaminophen

2.3 cm

Ibuprofen

3.2 cm

Caffeine

1 cm

RF 2.7 cm =0.77 3.5 cm 2.3 cm =0. 6 6 3.5 cm 3.2 cm =0. 91 3.5 cm 1 cm =0. 29 3.5 cm

Unknown Rf Values -

Distance from solvent front: 3.5 Compound

Distance Traveled

RF

Unknown 1

Spot 1: 1.1 cm Spot 2: 3 cm

Spot 1: Spot 2:

Unknown 2

Spot 1: 1 cm Spot 2: 2.2 cm Spot 3: 2.8 cm

Spot 1: Spot 2: Spot 3:

Unknown 3 TLC Plate

Spot 1: 2.5 cm

Spot 1:

1.1 cm =0.31 3.5 cm 3 cm =0. 86 3.5 cm 1 cm =0. 2 9 3.5 cm 2.2cm =0. 6 3 3.5 cm 2.8 cm =0. 8 0 3.5 cm 2.5 cm =0. 71 3.5 cm

3

Discussion: The goal of this experiment was to determine the unknown components of three unknown drug mixtures by analysis of thin layer chromatography (TLC) and comparing the three unknown drug mixtures to four known drug mixtures: Aspirin, Acetaminophen, Caffeine, and Ibuprofen. This was achieved by first adding 5 mm of 1:1 ethanol/ dichloromethane to a 100-mL beaker. Then obtaining a TLC strip, drawing a baseline, and using a pipette to place a drop of each drug mixture—Aspirin, Acetaminophen, Caffeine, Ibuprofen, Unknown one, two and three-- on the baseline of the TLC strip, ensuring use of a different pipette for each compound to avoid cross contamination. Then placing the TLC strip vertically in the 100-mL beaker containing 1:1 ethanol/ dichloromethane covered with a wash glass and allowing the solvent front to diffuse about 75% of the way up the plate. Upon removing the strip, the solvent front was marked and measured from the baseline to the solvent front at 3.5 cm. Then placing the strip under UV light and marking the center of greatest intensity for each of the drug mixtures. Finally, calculating the RF values for all of the drug mixtures, and comparing the known drug mixtures to the unknown. Based on the experimental RF values for these compounds, we can determine the relative polarity of the drug mixtures. The spots and their RF values are due to polarity. Caffeine had the

4 lowest RF Value of 0.29, revealing the compound had the highest affinity for the polar surface of the TLC plate and traveled the shortest distance from the baseline. Allowing us to infer that that Caffeine is most polar compound. The high polarity of Caffeine is most likely a result of the twoelectronegative amine and amide groups within Caffeine’s structure. The second most polar molecule, was acetaminophen with an RF value of 0.66. Acetaminophen’s polarity was likely due to the presence of an amide and hydroxyl group within the compounds structure. The third most polar molecule was Aspirin, with an RF value of 0.77. The polarity of aspirin is due to the carboxylic acid and ester groups within the compounds structure. The least polar out of the four known compounds was Ibuprofen, with an RF value of 0.91. This is likely due to the carboxyl group being less polar, and thus having less affinity for the TLC plate in comparison to the other three known compounds. Conclusion: In unknown drug mixture one, the recorded RF values were 0.31 and 0.86. These values were close to those obtained from aspirin (0.77) and caffeine (0.29). Therefore, unknown one was likely composed of caffeine and aspirin. In unknown drug mixture two, the recorded RF values were 0.29, 0.63, and 0.80. These values most closely correlate with that of caffeine (0.29), acetaminophen (0.66) and aspirin (0.77), reveling that unknown two is likely composed of these three compounds. In unknown drug mixture three, the recorded RF value was 0.71. Which is closest to that of aspirin (0.77), so unknown three was likely composed of aspirin. The book contains a table of major commercial drugs and their components. Based upon the table, Anacin contains aspirin and caffeine, indicating that unknown one is Anacin. Excedrin contains aspirin, acetaminophen, and caffeine, thus unknown two is likely Excedrin. Aspirin is composed of only Aspirin, therefore unknown three must be Aspirin.

5 Following the completion of this experiment, all of the unknown compounds were able to be identified using TLC analysis. Unknown one’s components matched up with that of Anacin. Unknown two’s RF values marched up with that of Excedrin. Lastly, unknown three’s RF values marched up with that of aspirin. None of results suggested the presence of Ibuprofen in the unknown drug mixtures.

Questions: 1. If the TA accidently made the solution using diethyl ether instead of ethyl acetate, the RF values would have been significantly lower. As diethyl ether is less polar than ethyl acetate, causing the polar compounds to not travel as far, less polar compounds to move further up the TLC plate, and a longer solvent front. As the compounds would have less affinity for the eluent solution, suggesting a decrease in RF values. 2. Phenacetin and acetaminophen are both composed of a benzene ring and secondary amide, yet the functional group located para to the amide on the benzene ring is an ester group in phenacetin and an alcohol group in acetaminophen. The ester group will cause phenacetin to be relatively less polar than acetaminophen. Therefore, phenacetin would have less affinity for the TLC plate, thus yielding a higher RF value. In summary, if the acetaminophen compound actually contained phenacetin, the RF value would have increased.

6 3. The chemical structure of Naproxen sodium is similar to the structure of Ibuprofen, as they both contain a benzene ring, with an alkyl group and a carboxylic acid. Thus, the two structures likely have similar functions and physiological effects....