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Experiments Overview

Thin layer chromatography - Determination of an analgesic mixture

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UV / VIS Spectrophotometer, UV Viewing cabinet, TLC spreader, Fielder guage.

TLC developing tanks, TLC glass plates 20cm x 20cm, 5um capillaries, vol. flasks 10ml.

Sample: Analgesic mixture provided.

Analgesics used are: aspirin, paracetamol (acetamenophen), caffein, and codeine.
Methanol, chloroform, toluene, diethyl ether, acetic acid, acetone.

Solutions preparation:

1. Solvent for standards, pure research grade Methanol.
2. Extraction solvent, 1:1 methanol / chloroform.
3. Analgesic standards, Provide a 0.001M for absorbance measurements by preparing a 100ml volume of 0.01M and then diluting 1 in 10.

Aspirin MW = 180.16 = 0.18g in 100ml = 0.01M
Paracetamol MW = 151.165 = 0.15g in 100ml = 0.01M
Caffein MW = 194.20 = 0.19g in 100ml = 0.01M
Codeine MW = 294.40 = 0.3g in 100ml = 0.01M

(2.5 ml made up to the mark in a 25ml vol. flask = 0.001M)

4. Developing solvent: Toluene 120mls, acetic acid 30mls, diethyl ether 30mls, methanol 20mls.
5. Analgesic mixture: grind together in the following proportions. Bottle and label A, B, and C.

Sample silica gel aspirin paracetamol caffein codein
A 4.0g 2.4g 1.6g 0.0g 2.0g
B 0.0g 4.0g 2.4g 1.6g 2.0g
C 2.4g 1.6g 0.0g 4.0g 2.0g

Analytical notes:

1. TLC plates: Make slurry with 25g silica gel and 62.5 mls water.
2. Apply 0.1mm thick silica gel layer on plates, using a fielder gauge to set thickness measurement on puller.
3. Give only one (1) sample mixture for analysis.
4. Digest 1.5g mixture with about 4 mls 1:1 chloroform/methanol, wash with more methanol through filter paper into a 10ml vol. flask and make up to the mark with methanol.
5. Make up fresh standards each week.

Operation of Instrument:

Follow User Guide: obtain help and advice from Demonstrator or Technician

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