CHEM2411LClayton State University

Dr. Michael KirbergerThin Layer ChromatographyTLC of analgesic drugs

Common analgesic DrugsDrug (brand name) IngredientsAnacin Acetylsalicylic acid, caffeineMotrin IbuprofenTylenol AcetaminophenVanquish Acetylsalicylic acid, acetaminophen, caffeine

Place about 10 mg of each of the four reference compounds (Ibuprofen, Acetylsalicylic acid, acetaminophen, and caffeine) in labeled test tubes and dissolve them in 1.0 mL few drops of methanol.

Place 10 mg of an unknown compound in a 5th tube and add 1 mL of methanol. Obtain 2 or 3 TLC plates. Carefully mark the origin line with pencil (1 cm from the bottom). Spot samples on origin line using capillary tubes. Spots should be at least 1 cm apart. Place plate in solvent chamber, allow the solvent (1:1:2 petroleum ether:methylene

chloride:ethyl acetate) to move up the plate until it is 0.5 cm from the top (Figure 1) Remove the plate from the solvent chamber and immediately mark the solvent front

with a pencil mark or small scratch. Examine chromatogram under a UV lamp and carefully circle any spots with a pencil.

Then place the plate in a jar of iodine vapor for approximately 30 seconds, remove, and circle any additional spots. Make sure to take the plate out of the solvent chamber as soon as the spots begin to show to reduce the possibility for over-exposure.

Calculate the Rf value for each component in the samples (Dsample/Dsolvent). From the identity and number of the spots in the unknown and the composition of the possible unknown, deduce the identity of your unknown common analgesic.

Figure 1: Spotted TLC Figure 2: Marked TLC Platesplate in solvent chamber after placement in iodine chamber