LABGUIDE
Determination of analgesics by thin layer chromatography (TLC)
Equipment:
UV / VIS Spectrophotometer, UV Viewing cabinet, TLC spreader, Feeler guage.
Apparatus:
TLC developing tanks, TLC glass plates 20cm x 20cm, 5um capillaries, vol. flasks 10ml.
Sample: Analgesic mixture provided.
Chemicals:
Analgesics used are: aspirin, paracetamol (acetamenophen), caffein, and codeine.
Methanol, chloroform, toluene, diethyl ether, acetone, acetic acid.
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
delloyd.50megs.com
|