Organic Chemistry 333L, section 03M LaboratoryPre-LabThin Layer Chromatography of Analgesics (TLC)By: Cameron Kahn14 January 2019TA: James Collie1 | P a g eObjective:In this experiment one will learn how to set up the apparatus and perform a thin layer chromatography analysis on various standard analgesics. The experiment will also teach one to calculate the Rf value and determine the identity of an unknown analgesic by comparing its Rf value to those of the standard analgesics[ CITATION Geo121 \l 1033 ]. By doing the experiment,one will learn to identify the content of over-the-counter analgesics. Theory:TLC is a simple, quick, and inexpensive procedure that gives the chemist a quick answer as to how many components are in a mixture. TLC is also used to support the identity of a compound in a mixture when the Rf of a compound is compared with the Rf of a known compound (preferably both run on the same TLC plate).A TLC plate is a sheet of glass, metal, or plastic which is coated with a thin layer of a solid adsorbent (usually silica or alumina). A small amount of the mixture to be analyzed is spotted near the bottom of this plate. The TLC plate is then placed in a shallow pool of a solvent in a developing chamber so that only the very bottom of the plate is in the liquid. This liquid, or the eluent, is the mobile phase, and it slowly rises up the TLC plate by capillary action.As the solvent moves past the spot that was applied, equilibrium is established for each component of the mixture between the molecules of that component which are adsorbed on the solid and the molecules which are in solution. In principle, the components will differ in solubility and in the strength of their adsorption to the adsorbent and some components will be carried farther up the plate than others. When the solvent has reached the top of the plate, the plate is removed from the developing chamber, dried, and the separated components of the mixture are visualized. If the compounds are colored, visualization is straightforward. Usually the compounds are not colored, so a UV lamp is used to visualize the plates.The retention factor, or Rf, is defined as the distance traveled by the compound divided by the distance traveled by the solvent.For example, if a compound travels 2.1 cm and the solvent front travels 2.8 cm, the Rf is 0.75:2 | P a g eThe Rf for a compound is a constant from one experiment to the next only if the chromatography conditions below are also constant:- solvent system- adsorbent- thickness of the adsorbent- amount of material spotted- temperatureSince these factors are difficult to keep constant from experiment to experiment, relative Rf values are generally considered. "Relative Rf" means that the values are reported relative to a standard, or it means that you compare the Rf values of compounds run on the same plate at the same time.The larger an Rf of a compound, the larger the distance it travels on the TLC plate. When comparing two different compounds run under identical chromatography conditions, the compound with the larger Rf is less polar because it interacts less strongly with the polar adsorbent on the TLC plate. Conversely, if you know the structures of the compounds in a mixture, you can predict that a compound of low polarity will have a larger Rf value than a polar compound run on the same plate.The Rf can provide corroborative evidence as to the identity of a compound. If the identity of a compound is suspected but not yet proven, an authentic sample of the compound, or standard, is spotted and run on a TLC plate side by side (or on top of each other) with the compound in question. If two substances have the same Rf value, they are likely (but not necessarily) the same compound. If they have different Rf values, they are definitely different compounds. Note that this identity check must be performed on a single plate, because it is difficult to duplicate all the factors which influence Rf exactly from experiment to experiment [ CITATION Dep13 \l 1033 ].Procedure:REMINDER: Close and cap all reagent and waste containers.Start by obtaining a TLC plate and jar. Next pick an end of the TLC plate and make a light pencilline about 1 cm from one side to the other (this will now be the bottom of your TLC plate). Nowadd the TLC solvent system made of 95% ethyl acetate / 5% acetic acid to the TLC jar. Make sure the solvent does not go above 1 cm the TLC plate. Check this by placing the TLC plate beside the jar and eyeing the line you placed on the TLC plate. Now spot one small circle of each of the three standards (standards: aspirin, acetaminophen, caffeine, ibuprofen) and one unknown onto the pencil line on the TLC place. Take CAUTION: to make sure that the spots areapplied along the drawn pencil line. Label these spots lightly with a pencil and make sure not to dig deep into the TLC place with the pencil[ CITATION Geo121 \l 1033 ]. Now gently place the TLC plate into the jar, and be sure not to splash the solvent on the paper nor should the solvent go higher than 1 cm. Wait for the solvent to reach approximately 1 cm to the top of the plate, remove the plate, and draw a line where the solvent has traveled. This is known as the solvent front. Now take the UV light and observe your TLC plant. Place circles around the highlighted spots. Now measure the distance from the center of each spot to the pencil line and record the values. Next, measure and record the distance travelled by the solvent (starting from the pencil 3 | P a g eline). Use this information to calculate the Rf value of each of the spots, and compare this information with the Rf value of the unknown. With this information, determine the identity of the unknown.Apparatus:Figure 1: UV LightFigure 2: TLC Apparatus4 | P a g eReagent Table:Name StructureMolecularweight(g/mol)Meltingpoint (oC)Boilingpoint(oC)Density(g/mL)Ethyl AcetateC4H8O288.10 -83.6 77.1 0.8945Acetic AcidCH3COOH60.0524 16.6 117.9 1.0492MethanolCH3OH32.042 -98 64.6 0.791AspirinC6H8O4180.1598 135 140 1.35AcetaminophenC8H9NO2151.1646 169 - 1.293CaffeineC8H10N4O2194.1926 238 - 1.23IbuprofenC13H18O2206.28 76 - -Mechanism-No mechanisms for this labDisposal:Please dispose of the TLC plate in the proper container, and this does not mean throwing it in thetrash can! The excess standard solution can be washed down the drain with excess water. The 5 | P a g eorganic solvents go in the predestinated organic liquid waste containers. Soiled gloves and