Pre lab 4

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University Of Georgia *

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2211L

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Chemistry

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Dec 6, 2023

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Title: Using Thin Layer Chromatography to Separate and Identify Unknown Mixtures Introduction: In this week’s lab, various active ingredients of six unknown analgesic mixtures were identified using thin layer chromatography. Thin Layer Chromatography is a chromatography technique used to separate the components of a mixture using a thin stationary plate. Is an indispensable organic laboratory technique that is used in three primary ways: compound purity determination, compound/multi-component mixture identification, and monitoring the progress of a chemical reaction. The purpose of this lab was to use TLC to result in separate spots formed by different compounds to view under ultraviolet light. Table of Reagents: Name: Structure: MW (g/mol): MP (  C): BP (  C): Density (g/cm^3): pKa: Acetaminophe n 151.2 169 ------ ----- ----------- ------ ----- Acetylsalicylic acid 180.2 135 ------ ----- ----------- ------ -----

Caffeine 194.2 235- 238 ------ ----- ----------- ------ ----- Ibuprofen 206.3 75- 77 ------ ----- ----------- ------ ----- Methylene chloride 84.93 ------ ------ - 39 1.33 ------ ----- Ethanol 46.1 ------ ------ - 78 0.7893 ------ ----- Ethyl Acetate 88.1 ------ ------ - 75 0.902 ------ ----- Acetic Acid 60.1 ------ ------ - 117 1.048 4.75 Safety Information:  Safety glasses, lab gloves, and lab coat must be worn during the entire experiment.  Use caution as the spotting capillaries are very sharp and fragile. Dispose in proper waste receptacle.

 Both methylene chloride and ethyl acetate are highly flammable so avoid sparks, flames, and hot surfaces.  Methylene chloride is highly carcinogenic. Make sure snorkels are turned on a working properly before dispensing liquids.  Avoid breathing any fumes or allowing any liquid to come in contact with skin.  Acetic acid causes severe burns if contacted with eyes or skin.  Be careful when dispensing liquids.  Any vapor or liquid exposure should be reported immediately.  Dispose of all liquid waste in appropriate bottle in fume hood. Experimental Procedure:  Place a small amount (tip of a spatula) of each of the 6 powders into separate test tubes.  Add about 1 mL of a 1:1 ratio of methylene chloride/ethanol solution to each test tube to dissolve the samples. Label each test tube with its corresponding “unknown” number to keep track of which sample is what.  With the three pre-cut TLC plates, lightly draw a line approximately 1 cm from the bottom edge of each plate. Be cautious to not press too hard so the silica gel doesn’t get scraped away. Make the line faint, but visible.  On the first plate, label four lanes to indicate where each “known” analgesic compound will be spotted. Ib corresponds to ibuprofen, Act corresponds to acetaminophen, Caf corresponds to caffeine and Asp corresponds to aspirin (acetylsalicylic acid).  Spot each of the know analgesic compounds on the origin line using capillaries which should be approximately 5mm apart.

 Construct a developing chamber with a 100-150mL beaker and watch glass. Add enough developing solvent to barely cover the bottom of the beaker. Don’t add too much.  Place the TLC plate into the chamber with the labeled side facing the interior of the beaker. Cover with a watch glass. Monitor as the solvent elutes up the plate.  When the solvent travels to within 1 cm of the top of the plate, remove it and draw a line. Do this immediately.  Repeat with the other two TLC plates. Spot and label them appropriately with three samples per plate. Run them separately and draw a line when done developing.  When all three have been completed, look at them using an ultraviolet lamp. The components will stand out clearly against the fluorescent green silica gel.  Circle all the dark spots visible on the plate carefully.  Record the data. Data and Observations:

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