食品分析(英文课件)：Thin Layer Chromatography

1、Thin Layer Chromatography (TLC,Key Points,General principles and procedures Application in food analysis,Standard phase silica plates (stationary phase) will be used. Apply reaction mixture in solution to the plate and then run the plate by allowing a solvent (or combination of solvents) to move up

2、the plate by capillary action. Depending on the polarity of the components of the mixture, different compounds will travel different distances up the plate,Thin Layer Chromatography TLC,Steps for TLC,1) Cut TLC plates. 2) Determine an appropriate solvent system. A good solvent system is one that mov

3、es all components of your mixture off the baseline, but does not put anything on the solvent front - Rf values between 0.15 and 0.85. 3) Fill TLC chamber with 12 mL of the desired solvent system. Place a large piece of cut filter paper in the chamber as well. 4) Spot the compound on the baseline of

4、the TLC plate. 5) Run the TLC. Let the solvent go about 90% of the way up the plate. 6) Remove the plate from the chamber and mark the solvent front immediately with a pencil. You will use this to calculate the Rf. 7) Let the solvent dry off of the plate. 8) Visualize the TLC using non-destructive t

5、echnique(s). The best non-destructive method is the UV lamp. 9) Visualize the TLC using a destructive method. This will be critical for compounds that are not UV-active. 10) Revise your choice of solvent system based on the results of your initial TLC. 11) Label your TLC, calculate the Rf for each s

6、pot and draw a picture of it in your notebook,The measure of the distance a compound travels is called the Rf value. This number, between zero and one, is defined as the distance the compound moved from the baseline (where it was originally spotted) divided by the distance the solvent front moved fr

7、om the baseline,Thin Layer Chromatography TLC,General procedure of TLC,Preparation and activation of plates Spot the compound on the base line of the TLC plate Run the TLC Visualize the TLC with non-destructive or destructive techniques,Planar Chromatography /“Opening column,Preparation of plates,sl

8、urry of adsorbent on glass/plastic/aluminum foil plate stationary phase: adsorbentmaterial-silica gel,aluminium oxide, or cellulose(blotter paper) mixing the adsorbent with a small amount ofinertbinder likecalcium sulfate(gypsum) and water spread and dries to make a film over surface dried andactiva

9、tedby heating in an oven for thirty minutes at 110C. after activation all plates must be stored in desiccator until used,thickness of the adsorbent layer : analytical purposes :0.1 0.25mm preparative TLC:0.5 2.0mm,Eluent and Specific color reagents,Eluent For silica gel coated TLC plates, the elutan

10、t strength increases in the following order: Perfluoroalkane(weakest),Hexane,Pentane,Carbon tetrachloride,Benzene/Toluene,Dichloromethane,Diethyl ether,Ethylacetate,Acetonitrile,Acetone,2-Propanol/n-Butanol,Water,Methanol,Triethylamine,Acetic acid,Formic acid (strongest) Specific color reagents E.g.

11、 diphenylamine, dimethylaniline,Spot method,Application,Thin Layer Chromatography (TLC) is an extremely useful technique for monitoring reactions and determining the purity of a substance . It is also used to determine the proper solvent system for performing separations using column chromatography,

12、Application,Qualitative analysis（Rf ） Quantitative analysis Elute the compound on the plate and detect the absorbance Scan the spot density on the plate with UV scaner,Saccharides, amino acid, vitamine, aflatoxin, pesticide, etc。 One of chromatographic technique (GC, HPLC) Advantage： separate many sample at a time （HPTLC） very simple to use and inexpensive The solvents for the TLC plate can be changed easily and it is possible to use several different solvents depending on your desired results. disadvantage ： may not be reproducible the detection limit i