Introduction: The purpose of this lab was to determine the composition of four different over-the-counter drugs (Anacin, Bufferin, Excedrin, and Tylenol). These compositions were determined by using the method of thin-layer chromatography (TLC) of the four over-the-counter drugs, which were then compared to four different components of drugs (acetaminophen, aspirin, caffeine, and salicylamide). Experiment Scheme1: Figure 1. Structure formulas1 Under an open flame in the hood, 12 capillary micropipettes were made. Two silica TLC plates were obtained, along with a development chamber.
Each plate was prepared and labeled appropriately with a lead pencil. The first plate was spotted with acetaminophen, aspirin, caffeine, salicyclamide, and reference. The second plate was spotted with Anacin, Bufferin, Excedrin, Tylenol, and reference. The development chamber was then brought to the hood where 0. 05% glacial acetic acid in ethyl acetate was poured into the chamber. The first plate was placed in the chamber until the solvent was approximately 0. 5cm from reaching the top. Once dry, the plate was placed under the UV light to observe the differences in the over-the-counter drugs.
A circle was drawn around each dot that formed so a measurement could be taken to help determine the Rf value. The same steps were taken with the second plate as were done with the first. After all observations and measurements were taken the two plates were both plates were placed in a chamber with iodine crystals and then was heated with body heat from the hands until the formation of dots was noticeable. Both plates were taken out and observed to find similarities and differences. Data: Name Formula MW (g/mol) Amount Moles State Density (g/cm3) Melting Point (°C) Boiling Point (°C) Theo. Yield Hazards Acetaminophen C8H9NO2.
151. 17 ______ _____ Liq. 1. 2639 169 >500 ____ Taken in bulk can lead to stomach problems Aspirin C8H9O4 180. 16 ______ ______ Liq. 1. 4 136 140 _____ Anemia, gastrointestinal, allergies, hives, tinnitus, Reyes Syndrome Caffeine C8H10N4O2 194. 19 ______ ______ Liq. 1. 23 238 178 Metabolic stimulant dependency, restless, anxiousness, irritability, addiction Salicylamide C7H7NO2 137. 14 ______ _____ Liq. 1. 33 140 181 Emits toxic fumes, harmful if swallowed Table 1. Pre-lab chemical information1 Name Distance spot traveled (cm) Distance of solvent (cm) Rf Value (cm) Acetaminophen 3. 9 5. 7 0. 68 Aspirin 5. 2 5. 7 0. 91 Caffeine 2.
8 5. 7 0. 49 Salicylamide 4. 9 5. 7 0. 86 Table 2. Rf values of the reference plate (plate one) Name Distance spot traveled (cm) Distance of solvent (cm) Rf Value (cm) Anacin 1. 9 5. 9 0. 32 Bufferin 5. 1 5. 9 0. 86 Excedrin 1. 8 4. 1 5. 9 5. 9 0. 31 0. 69 Tylenol 4. 1 5. 9 0. 69 Table 3. Rf values of the sample plate (plate two) Discussion: The TLC experiment was designed to determine the components of Anacin, Bufferin, Excedrin, and Tylenol by comparing the physical observations and the statistical data (RF factor) on the sample plate to that of the reference plate; which had acetaminophen, aspirin, caffeine, and salicylamide.
The development solvent, ethyl acetate with 0. 5% glacial acetic acid, was used in the chamber because the acid supplied protons and suppressed ionization which in turn allowed the spot to travel upward instead of staying stationary. 1 The ultimate goal was to find out which components were present within the over-the-counter drugs and which components were not. This would differentiate the use for each of the drugs as well. Under the UV illumination, one spot formed for each crosshair of the reference plate, while multiple spots were formed for each cross hair on the sample plate.
As is shown in figure 2, the spots closer to the top (aspirin, salicylamide, and reference) are lighter in color and are more fluorescent, where as the spots closer to the bottom are more of a darker color without any appearance of fluorescence. Due to the appearance of the spots on each plate, a preliminary assumption of the components in each medication was determined. It was concluded, by strictly looking at the spots and their colors, that Anacin’s component was caffeine, Bufferin’s component was between aspirin and salicyclamide, Excedrin’s components were caffeine and acetaminophen, and Tylenol’s component was acetaminophen.
The appearance of the spots under the UV illumination was not enough to determine the specific components in each over-the-counter drug, so the Rf values were evaluated to further conclude the experiment. The Rf value is the ratio of distance travelled by the solute to the distance travelled by the solvent front. 2 According to table 2 and table 3, a comparison can be made between the Rf values. Anacin’s component is caffeine, Bufferin’s component is salicylamide, Excedrin’s component’s are caffeine and acetaminophen, and Tylenol’s component is acetaminophen.
These results, as compared to the those of the UV illumination, are similar, except for Bufferin. In the UV illumination, it was hard to determine which spot was closest to the that of Bufferin when comparing it to the reference plate because aspirin and salicylamide appeared to be very similar in distance. After the Rf values were determined, it was easier to see that Bufferin’s component (table2 and table 3) was salicylamide due to fact that they shared the same Rf value, 0. 86 cm. While looking at the TLC plates under the UV illumination, an ‘X’ was not placed within the circles that were fluorescent.
This source of error was particularly distinct when looking at the data and making conclusions about which components were in each of the over-the-counter drugs. Without the mark, it was hard to differentiate between aspirin and salicylamide when comparing it to the reference spot on the same page, and in comparing it to the sample plate. It was unclear to determine which of the two components were present in Bufferin. Next time, the spots will be marked appropriately as stated and those that fluoresce will receive an “X”2.
Another error that was encountered was mishandling of the plates. It was stated to handle the plates with care and to avoid touching the top because residue would affect the experiment. The oils that are on the body could potentially throw off the result, which in turn leads to misleading data to interpret. It wasn’t until the plate (reference) was placed within the iodine chamber that a fingerprint became noticeable closer to the top. Although it may or may not have caused any significant skews in the data, it was a precaution that was overlooked.
Next time, tweezers should be used more often and in the off chance that the hands need to hold the plate, it would be important handle from the edges instead of a big portion on the top. According to the information that was gathered and evaluated from the thin-paper chromatography under UV illumination and iodine analysis, the components of all four of the over-the-counter drugs were determined therefore the goal of the experiment was achieved. Questions2: 4. If the spotting on the line and positions marked on the plate were with a ballpoint pen, the ink would travel with the development solvent as the experiment continued to carry on.
The pigments and components of the pen would separate as it advanced and the data would not be useful due to the fact that the ink contamination. 5. It is possible to distinguish between two spots that have the same Rf value, even if they are representing two different compounds. One way to distinguish a difference is by looking at the plate under UV illumination. Under the light, the spots will appear differently and their colors will be different therefore they will be able to be distinguished as different compounds.
Another way to tell a difference is by using an iodine chamber and heating it with body heat until spots appear on the plates. The two plates show different brown spots according to the components they have within them. The difference in the tone of the color would be another alternative route in distinguishing the difference between two compounds.
References: 1. Rxlist the internet drug index. (2012, February 15). Retrieved from http://www. rxlist. com on January 26, 2013 2. Radke, K. , Stolzenberg, G. “Organic Chemistry: Laboratory Manual”, 3rd ed. Cengage Learning. N. D. 2009.