RHYS LEWIS, AHS, DECD, UNISA / JON BAUGH / SCIENCE PHOTO LIBRARY RHYS LEWIS, AHS, DECD, UNISA / JON BAUGH / SCIENCE PHOTO LIBRARY
Thin-layer chromatography. Animation showing the use of the analytical technique of thin-layer chromatography (TLC) to separate food dyes. The sample has been prepared and placed on the TLC plate which is standing in a jar saturated with the solvent hexane. The solvent rises up the plate by capillary action, creating an advancing solvent front. The food dyes in the sample are drawn up the plate with the solvent, but rise to different heights depending on how much they bond to the silica in the TLC plate. Molecules of the food dyes move over the silica, swept along by the molecules of hexane solvent. This is shown in the animation for three food dyes (yellow, red and blue), with molecular structures and hydrogen bonding shown to account for the different amount of bonding for each food dye. The yellow food dye contains carbonyl and amine groups. The red food dye is shown with hydroxyl groups. The blue food dye does not contain chemical groups that bond strongly to the silica. The final scene shows the distances moved by the food dyes being measured and used to calculate a ratio called the retention factor (Rf). For the preparation of the sample and TLC plate, see clip K005/3728. For this animation with labels, see clip K005/3730.
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