Experiment 1: TLC Analysis of Analgesic Drugs 1/23/2011 Purpose: The goal of this experiment is to test our knowledge and understanding of TLC analysis by having us do a TLC analysis of analgesics to figure out their main chemical components. Calculations: 1. ) Rf = Distance spot traveled/ distance solvent traveled Results: Table 1: TLC Analysis Analgesic Drugs| Rf Value| Acetaminophen| 0. 323| Aspirin| 0. 597| Caffeine| 0. 081| Unknown 154 (Plate 1)| 0. 081, 0. 306, 0. 597| Ibuprofen| 0. 698|
Salicyclamide| 0. 587| Unknown 154 (plate 2)| 0. 079, 0. 397, 0. 587| Discussion: The goal of this experiment was to use TLC Analysis to determine the analgesic drug present in the unknown solution 154. One observation of the unknown spotting solution was that it was cloudy. After forming the unknown spotting solution it was then heated to make it a more saturated solution thus enabling the spots on the TLC plate to contain more of the drug making it easier to compare it with the other drugs.
After the TLC plates were developed and visualized first through UV light and then through an Iodine chamber ( though no more spots were visualized with iodine chamber) , Rf values were then taken of each spot on the plate. The Acetaminophen had a value of 0. 323, Aspirin had a value of 0. 597, Caffeine had a value of 0. 081, Unknown 154 on the first plate had 3 different values; 0. 081, 0. 306, 0. 597, Ibuprofen had a value of 0. 698, Salicylamide had a value of 0. 587, and Unknown 154 on the second plate had three different values as well; 0. 079, 0. 97, and 0. 587. Through analysis it was determined that unknown 154 was Aspirin. This was found by comparing the Rf values of all the analgesic drugs to unknown 154. After comparing them it was seen that the Rf value for Aspirin matched one of the Rf values for unknown 154 exactly. The determination of the unknown was further supported by looking at the samples in solution. Both the unknown 154 and Aspirin were cloudy in solution thus further supporting the identification of unknown 154. In this experiment there were not too many sources of error.
One source could have been that the glassware being used may not have been cleaned thoroughly before using it thus possibly contaminating the unknown or the other analgesic drugs. This Experiment definitely was an efficient way to help determine what type of drug the unknown 154 was but there are a few improvements that could have been done to help better determine the unknown. One improvement could be to examine the solvent used because different solvents create different separations between spots.
Another improvement could be to also run an Infrared Spectroscopy on the unknown and known compounds. Answers to Questions: 1. ) When running TLC plates three common mistakes that can be made are using a pen instead of a pencil to mark on the plate, using the wrong solvent, and touching the plates thus getting grease on them. 2. ) The Starting line and the spotting line are marked with pencil rather than pen because the ink from the pen would move with the solvent front thus interfering with the results. 3. ) Acetaminophen Aspirin Caffeine
Ibuprofen Salicylamide Pretty much all of the functional groups can determine the polarity of a compound. This includes Amides, Acids, Alcohols, Ketones, Aldehydes, Amines, Esters, Ethers, and Alkanes. Even though they all can determine the polarity of the compound Amides, Acids, Alcohols, Ketones, and Aldehydes are the most polar and therefore are the best at determining polarity in compounds. 4. ) In order of increasing polarity Ibuprofen is the least , then it is Aspirin, then Salicylamide, then acetaminophen, and Caffeine is the most polar. 5. The Acetic Acid in the TLC solvent is used to increase the polarity of the developing solvent thus reducing the amount of attraction the polar compound has for the stationary phase. 6. ) TLC is a good way to determine an unknown, but not to determine composition of an unknown. One good way to determine the composition of an unknown is to run an Infrared Spectroscopy which when analyzed functional groups can be identified. Another way to determine the composition of an analgesic drug could be to run a Mass Spectroscopy which when analyzed could determine the elemental composition of the drug.