TLC Pre Lab cf - Introduction, Table of Reagents, and Procedure Sections of TLC Lab Report PDF

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Introduction, Table of Reagents, and Procedure Sections of TLC Lab Report...

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Thin Layer Chromatography (TLC): Identification of Unknown Mixtures Introduction The purpose of this experiment is to identify the active ingredients of six unknown analgesic mixtures as well as match the unknowns to their commercial names. In order to identify the various active ingredients, the new technique of thin layer chromatography is employed. Thin layer chromatography has multiple purposes. This method can determine the purity of a compound, identify components of a mixture, and monitor chemical reactions as they progress. Thin layer chromatography, a type of solid-liquid chromatography, separates components of a mixture based upon each compound’s affinity for a mobile phase or a stationary phase. This method of chromatography depends on how strongly a compound is absorbed into a stationary phase. Varying compounds are held to the specific adsorbent used to differing degrees. Once the absorbent is added to the solution of organic compounds, the components of the solution are adsorbed onto the surface of the solid. Based on the structure of the compound, each component in the mixture is bound to the adsorbent via Lewis acid-Lewis base interactions, dipole-dipole interactions, and various intermolecular interactions. The stronger the absorption of a compound into the stationary phase, the slower it progresses through the system, thus resulting in the separation of the mixture’s individual components. Thin layer chromatography is thus named because it takes place on a glass surface that is coated with a thin layer of the chosen adsorbent. Once the organic solution has been placed upon the glass plate, the chromatography takes place as a solvent moves across the plate through capillary action. The choice of solvent is key as the solvent’s polarity, along with the polarity of the compounds, determines the distance each component moves up the plate and separates. Polar compounds will have stronger interactions with the polar stationary phase and thus progress slower. A constant called the retention factor (Rf) can be calculated by dividing the distance the compound traveled by the distance the solvent traveled. The chosen solvent should produce an optimal retention constant between 0.3 and 0.7 as the values can range from 0 to 1. An appropriate solvent should travel up to one third to two thirds of the plate. The ratio of the distances of the compounds to the distance of the solvent front is the measure of the plate. Each substance is spotted onto the plate at the line of origin. The edge of the stationary phase is positioned in a thin layer of the mobile phase. The chromatography is run until the mobile phase reaches the far end of the plate. The solvent is evaporated under a UV light. Each compound is observed as a dark spot on the plate at the point at which the chromatography halted. Safety/Materials Table of Reagents

Compound Name

Structur e

Molecular Weight (g/mol)

Melting/Boiling Point (C)

Density (kg/m3)

pKa

acetaminophen

151.163 g/mol

MP: 196C

N/A

N/A

acetylsalicylic acid

180.157 g/mol

MP: 136C

N/A

N/A

caffeine

194.19 g/mol

MP: 238C

N/A

N/A

ibuprofen

206.29 g/mol

MP: 76C

N/A

N/A

methylene chloride

84.93 g/mol

BP: 39.6C

1330 kg/m3

N/A

ethanol

46.068 g/mol

BP: 78.37C

789 kg/m3

N/A

ethyl acetate

88.11 g/mol

BP: 77.1C

897kg/m3

N/A

acetic acid

60.05 g/mol

BP: 118.1C

1050kg/m3

4.75

Mixture Composition Table Analgesic Mixture

Known Components

Anastasia’s Analgesic Elixir

acetaminophen

acetylsalicylic acid

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Excedrin

acetaminophen

caffeine

acetylsalicylic acid

Excedrin AF

acetaminophen

caffeine

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Tylenol

acetaminophen

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Motrin

ibuprofen

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Patrick’s Potent Powder

caffeine

ibuprofen

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Table of Reagents and Corresponding Safety Precautions Compound Name acetaminophen acetylsalicylic acid caffeine

Safety Precautions Causes genetic defects in germ cells. Organ toxicity after single exposure and/or repeated exposure. Toxic to aquatic environments. Acute oral toxicity. Causes serious eye damage. Reproductive toxicity. Organ toxicity after single exposure. Acute oral toxicity. Acute toxicity if inhaled. Reproductive toxicity. Toxic to aquatic environments. Acute oral toxicity. Reproductive toxicity. Organ toxicity after single exposure and/or repeated exposure. Toxic to aquatic environments.

ibuprofen

methylene chloride

Extremely flammable. Acute oral toxicity. Causes serious eye and skin irritation. Suspected carcinogen. Organ toxicity after single exposure and/or repeated exposure. Toxic to aquatic environments.

ethanol

Extremely flammable. Causes serious eye damage. Organ toxicity to respiratory tract. Organ toxicity after single exposure and/or repeated exposure. Carcinogen. Reproductive toxicity.

ethyl acetate

Extremely flammable. Causes serious eye damage. Acute toxicity if inhaled.

acetic acid

Flammable. Acute dermal toxicity .Causes severe burns and eye damage. Organ toxicity after single exposure. Toxic to aquatic environments.

Additional Safety Precautions Wear appropriate lab attire at all times including safety glasses and gloves. Many of the reagents for this experiment can cause serious damage to the eyes and skin. Take care when handling the spotting capillaries as they are fragile and sharp. Many of the reagents are also highly flammable. Be cautious when handling and keep them away from open flames and sparks. Furthermore, methylene chloride and ethanol are carcinogens. Always work under a fully functional snorkel and avoid inhaling any vapors. Dispose of all waste in the designated containers.

Procedure 1. Place a small portion of each of the sic unknown solids into individual test tubes. Label each test tube with the unknown code of each sample. 2. In order to dissolve the solids, add about 1mL of 1:1 methylene chloride/ethanol solution to each test tube. 3. Lightly sketch origin lines approximately 1 cm from the bottom edge of each precut TLC plate. Be cautious not to remove any silica gel by applying too much pressure with the pencil. 4. Further label the first plate by marking four lanes indicating where each known analgesic compound is spotted along the origin line. There should be four known compounds: ibuprofen (Ib), acetaminophen (Act), caffeine (Caf), and acetylsalicylic acid (AspirinAsp). 5. Use the capillaries to spot each of the known compounds, provided dissolved in solution, on the origin line. They should be evenly spaced and there should be 5 mm between the first and last compound and the edge of the plate. 6. Using a 100-150 mL beaker and a watch glass, put together the developing chamber. 7. The TLC plates will be developed utilizing ethyl acetate containing 0.5% acetic acid. A quantity of solvent that barely covers the bottom of the beaker is added. The watch glass covers the beaker to prevent evaporation.

8. Once the solvent has traveled to about 1 cm from the top of the plate, remove it. Sketch a line across the solvent front. 9. Repeat this process using a developing chamber for the next two plates, each containing three of the unknowns. 10. After developing all of the plates, use an ultraviolet lamp to visualize them. Compared to the fluorescent green silica gel, the components will stand out clearly. Circle all visible dark spots lightly....