Analgesics and TLC

Abstract: Briefly describe the purpose of today experiment.
Procedures: Provide the reference to the procedure. Please state if any changes were made to the procedures. If there’s any, explain the changes you have made to today experiment.
Structure or reaction of compound interest: Draw the structure of compound.
Data and calculation:
Discussion, observation and Conclusion
Possible source of error?
caffeine; Baeyer Aspirin™ = acetylsalicylic acid; Excedrin® = acetylsalicylic acid, acetaminophen and caffeine; Tylenol® = Acetaminophen.
To identify an unknown by TLC (and also to monitor the progress of a reaction), the typical strategy is to run chromatograms of known substances [the standards) and the unknown at the same time (in parallel lanes). If the unknown has one or more spots that correspond with the same fl/values as the standards, then those substances are probably present
Chemicals & Equipment:
• One Silica gel 60 F254 TLC aluminum sheet (pre-cut, 50 x 100 mm)
• One TLC developing chamber (Ball mason jar with paper wick and lid)
• 10 mL graduated cylinder and ~12 mL 65% EtOAc, 30% Hexane, 5% HOAc developing solution
• 2 mL 50:50 ЕЮН/СН2СІ2
• Graduated plastic disposable pipette
• One sharpened No. 2 pencil
• One open-ended glass capillary spotter
• One culture tube
• One unknown analgesic tablet
• Glass rod
• Ruler
• Filter paper
• Pestle
• TLC station with standard solutions of (a) acetylsalicylic acid, (b) acetaminophen, (c) caffeine, (d) ibuprofen, (e) (S)-Naproxen in 1 dram scintillation vials

Procedure:

(1) Thin-Layer Chromatography: Obtain the necessary equipment. Record the number of your unknown analgesic in the notebook and on the worksheet You and one other person will share a TLCdeveloping chamber—this is essentially a glorified mason jar. (Commercial chambers are also available, but this is just as good, if not better. The lids create a nice seal and have enough head space to fit tall TLC plates.) Important notes: (a) Be sure that your TLC chamber is dry! There should be no water in the jar. If there is, rinse the chamber out with acetone or developing solution (and gently pour the acetone into the hazardous waste container). Acetone will dissolve any unwanted organics and is miscible with water—it will evacuate quickly (bp 56 °С)! (b) Be sure that the lid is not rusted and that there is a new rubber seal around the inside metal top. Obtain a new lid from your instructor if yours needs replacing, (c) Be sure that your jar has a wick inside. This will ensure the solvent will climb the plate via capillary action. The wicks are made out of pre-cut filter paper.

(12) Another useful visualization technique is to use an iodine (h) staining chamber. Elemental iodine is a purple-black solid halogen that sublimes a "purple haze" at ambient temperature. Certain compounds (e.g. alkanes, alcohols, amides and ethers) do not absorb UV light sufficiently to quench the fluorescence of the TLC and therefore will not show up under a UV lamp. However, they will adsorb iodine vapors and can be easily detected. After the residual solvent has evaporated and the spots traced, place the TLC plate in the large glass iodine chambers located in the chemical fume hoods. Record which spots stain with iodine; this could be further evidence for the content of your unknown tablet These yellow-brown spots should be outlined with pencil immediately after removing the plate from the iodine chamber because the stain is reversible and as the I2 sublimes off the plate they will soon disappear. (However, some of the analgesics stain for quite some time.)(13) Calculations: Calculate the Rf values for every spot while the plate is staining and record the values in both your notebook and on the worksheet Draw your TLC plate with the separated spots on the worksheet space provided. By comparing Rf values of known standards with the Rf value(s) of the unknown spot(s), provide a reasonable and logical conclusion as to the identity of your unknown analgesic tablet You may 'eyeball' the spots to provide a superficial, qualitative argument Chromatogram parameters, the quantitative Rf data, and iodine staining should support your argument

(2) With a 10 mL graduated cylinder, add around 12 mL of TLC developing solution (65% ethyl acetate, 30% hexane and 5% glacial acetic acid) to the chamber. The total final volume may vary! The jar has a concave glass bottom that you want the solvent level to rise above slightly so there is a shallow reservoir of solution. That is, make sure the entire bottom is filled with solvent so that no free glass shows (but not too much!). Cap the lid and shake the jar gently so to saturate the paper wick with solvent [If you get this solvent on your hands, it will feel cold. This is because of the heat transfer (it is boiling off of you). You may notice a white precipitate on your fingerprints. This is actually not a compound, but rather the grease of your hand that the solvent dissolved and lifted as it evaporated. You may wash your hands, but it is not necessary. Hexane is a neurotoxin, do not ingest or inhale the solvent] It is important that the solvent level is below the spots at the origin on the TLC plate.(3) Once the chamber has been prepared with the wick saturated in developing solution it should be placed on the bench to not be disturbed. Once the experiment is in progress, do not pick up or move the chamber!

(9) Plate Development. Unscrew the lid and gently submerge the plate into the TLC developing chamber. Do not simply drop the plate inside haphazardly; rather slowly rest in the shallow layer of solvent (the level should not exceed die origin line). Lean the plate so the aluminum backing faces the wick (do not touch wick to silica gel). Collaborate with your chamber mate to delicately balance the plates on either side of the wick so that they do not touch but run simultaneously. Quickly seal the lid. Once sealed, the developing solution will slowly rises upwards by capillary action. Allow the chamber to remain undisturbed as the solvent travels up the plate. Do not pick up the chamber or tilt it(10) Plate development will require approximately 15 minutes. Observe the solvent level and once it has almost risen to the top of the plate (~ 10 mm) unscrew the lid and quickly mark the solvent level with your pencil. Mark the solvent front once the plate leaves the chamber! Solvent will begin to evaporate from the plate instantly1. Once the plate is dry, observe it under the UV light again. Notice that the spots have now uniquely traveled and separated. With pencil, lightly trace the exact outline of each spot on the TLC plate.(11) Measure the distance from the origin (baseline) to the solvent front Measure the distance from the origin to the midpoint of each spot Record this information in your notebook. The unknown analgesic may have one or more spots.