TLC Handout - CHE 231 Thin Layer Chromatography (TLC): Used...

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CHE 231 Thin Layer Chromatography (TLC): Used for monitoring separation of compounds using solvent extraction. Chromatography is a method for the separation and identification of substances (solutes) based upon their differential mobility on a supporting medium (stationary phase) under the influence of a flowing medium (mobile phase), which may be gas or liquid. Each component in a mixture interacts with (adsorbs on) the stationary phase and dissolves in the mobile phase to a different extent. Those that are bound less tightly to the stationary phase and are more soluble in the mobile phase travel farther than other components of the mixture. The various methods of chromatography differ with respect to the mobile phase (a liquid or a gas), the stationary phase (paper, gels, or solid packings) and the driving force for the motion of the mobile phase (pressure, gravity or an electric field). In thin-layer chromatography, a flat solid support such as a sheet of glass, plastic, or aluminum foil is coated with a thin layer of silica gel or alumina. The mixture of compounds to be separated is applied as small spots of a solution near one edge of the plate. This edge is immersed in a solvent that acts as the mobile phase, or eluent. The solvent moves upwards through the solid support by capillary action. In this experiment, you will determine the extent of separation/purity of each component after separation of three components from the mixture. None of the component will behave identically in thin layer chromatography on silica gel. The sample/solutions to compare are spotted on the TLC plate. To develop the chromatogram, put the plate in a solvent chamber of chloroform (CHCl 3 ), and allow the solvent to rise up the plate. Remove the plate and visualize the spots under UV light. You may then compare the behavior of each component to determine the purity. Record your observations as a diagram of each slide, and submit your conclusions and R f values in your lab report. Applying the Sample Your TA will provide you with TLC plates. The very thin or narrow-tipped glass capillary should be dipped into the solution to be applied and held there for 5 or 10 seconds until the solution has stopped rising in the capillary. Then touch the tip to the silica gel about 5 to 10 mm from the bottom (coated end) of the plate. You should be able to see the solution spreading onto the silica gel. Keep the spot as small as possible by lifting the tip of the applicator from the plate as soon as you see the solution spreading. You may want to touch the spot with the applicator again to make sure that you have transferred some solution to the plate but do not apply too much or your chromatogram will have poor resolution. Experience will show you how much solution to apply. Chromatograms for more than one sample can be obtained by placing other
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This note was uploaded on 02/26/2012 for the course CHEMISTRY 231 taught by Professor Uc during the Spring '12 term at Kentucky.

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TLC Handout - CHE 231 Thin Layer Chromatography (TLC): Used...

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