Purpose: In this experiment, TLC will be used to determine the composition of various over the counter Analgesics.
Observations, Data, Procedure, Results
The first thing we had to do is get 12 capillary micropipettes to spot the plates. In order to get these pipettes the way we want them, we had to place each one over the flame of a micro-burner and gently pull on it. If we pull it out too far it would result in getting very little sample and this would cause us not seeing any spots. After we prepared the micropipettes we went and four silica gel sheet plates to be used for spotting. The first plate we spotted had Acetaminophen and Aspirin. The second one had Ibuprofen and caffeine, and the third one had aspirin and Ibuprofen. We spotted them right on the 1.5 cm. line we drew on the plates. We did this three times for each one and then we waited for it to dry. After the reference plate has been spotted, we got a screw cap jar to use as our development chamber. In the chamber we poured the development solvent, which was 0.5% glacial acetic acid in ethyl acetate. We put the plates in there gently allowing the solvent to reach about 0.5 cm. to the top. This process took about 10 minutes. After it was done we waited till the plates dried, and then took the plates under the UV Visualization light to observe the spots. All the spots were purple, but the one with the Ibuprofen was a little faint and harder to see; we circled the spots on each plate and then took them back to our workplace to measure the distant, and to calculate the Reference Factor (Rf) for each one, which is: Rf = Distant of solute Distant of solvent
For the first plate (Acetaminophen & Mixture A) there were three spots and two of them were the same they measured at 3.4 cm; one of the spots was for the Mixture A and the other one was for the acetaminophen. The other one was for the Mixture A and it was measured at 4.4 cm. The Rf value for Acetaminophen is 3.5 cm/5 cm = 0.7 and the Rf values for Mixture A is 3.4 cm/ 5 cm = 0.6, & 4.4 cm/5 cm = 0.9. The second plate (Ibuprofen & Mixture B) also had three spots and again two of them were the same, the distance was measure at 4.7 cm one spot was for the Ibuprofen and the other for Mixture B, and the last spot was measured at 1.6 cm, which belonged to the Mixture B. The Rf value for Ibuprofen is 4.7 cm/ 5.1 cm = 0.92 and the Rf values for Mixture B were 4.7 cm/ 5.1 cm = 0.92 & 1.6 cm/ 5.1 cm = 0.31. The third plate (Aspirin & caffeine) only had two spots; the one for aspirin was measured at 4.6 cm, and the one for caffeine was measured at 1.5 cm. The Rf value for the aspirin was 4.6 cm/ 5.5 cm = 0.84 & the Rf value for the caffeine was 1.5 cm/ 5.5 cm = 0.27. Our professor had us do this again, but this time with an unknown analgesic tablet. We received unknown # 7 and we used a separate plate to test it. We used Acetaminophen as out other analgesic. We did all the same steps as before and after we took it out of our development chamber and put it under the UV light, we noticed two spots but the one that was supposed to be for the unknown was very faint just like the Ibuprofen. We went back to measure the distance. The distance for the Acetaminophen was 3.5 cm and the distance for the unknown was 4.8 cm. The Rf value for the acetaminophen is 3.5 cm/ 5.3 cm = 0.66 & the Rf value for the unknown is 4.8 cm/ 5.3 cm = 0.91. We determined the unknown had to be Ibuprofen, because the spot was faint and barely visible when we took it under the UV light just like our second plate.
Discussion
When we were preparing our development chamber we had to omit the liner because the TLC plates are very thin and if they touch the filter paper liner of the development chamber, the solvent will begin to diffuse onto the absorbent surface. We placed both reference mixtures in the same jar at the same time because the solvent needed to be the same. If the bottom edge of the plates weren’t parallel to the bottom of the jar, then