Thin Layer Chromatography (TLC)

Learn that thin layer chromatography separates compounds based on differing polarity. Examine TLC plates composed of silica gel on glass, which contain polar hydroxyl groups that interact with sample components.

Draw a pencil line near the bottom of the TLC plate. Use a capillary tube to spot the sample solution onto the plate at the pencil line, pressing gently two to three times to deposit the mixture.

Place a small amount of solvent in a developing chamber and position the spotted TLC plate so the pencil line sits above the solvent surface. Cover the chamber to prevent evaporation and allow the mobile phase to rise up the stationary phase by capillary action.

When the solvent approaches the top of the plate, remove it and immediately mark the solvent front with a pencil. Allow the plate to dry completely.

Use UV light or a staining agent like iodine to reveal the location of separated components on the plate. Under UV light, use protective glasses and trace visible spots with a pencil. Alternatively, dip the plate in stain, rinse, and heat until spots appear.

Measure the distance from the spotting line to the center of each spot and divide by the distance from the spotting line to the solvent front. This yields the Rf value for each component, ranging between zero and one.

Use TLC to track reaction progress by spotting the reaction mixture before and after reagent addition. Compare Rf values of reactant and product spots to determine reaction completion.

Test various solvent mixtures (hexanes, ether, ethyl acetate, dichloromethane) by running TLC plates to find a system that maximizes separation of target components. Select a solvent system where components are well-separated with one near the top and one near the middle of the plate.