Depending on the polarity of the components in a

Depending on the polarity of the components in a mixture, different compounds will
travel different distances up the plate. More polar compounds will have interactions with
polar stationary phase and therefore will travel slower. Non-polar compounds will be
present in the solvent more (due to less interaction with stationary phase) and will travel
faster (larger distance) on the plate. The relative distance moved by the component with
respect to the distance moved by the solvent is called Rf values, which can be calculated
by:
Rf = distance moved by a component
distance moved by solvent
Tips for TLC
Cutting TLC plates: Silica plates are bought as glass pieces that are cut using diamond
tipped glass cutter after scoring it using a ruler and pencil lightly. (This process is
frustrating in the beginning but you will become comfortable with some practice)

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Determination of appropriate solvent: The compounds will travel different distances
depending on the solvent you choose. In non-polar solvents, polar compounds will not
travel, while the non-polar compounds will travel up the plate. A good system therefore
is the one that moves all components in a mixture off the baseline but does not put any
component on the solvent front. (This is not always possible)
Some solvents and their polarity:
Very Polar Methanol> ethanol> isopropanol
Moderately Polar Acetonitrile>ethylacetate> dichloromethane>diethylether>Toluene
Non-Polar Cyclohexane, petroleum ether, ether, hexane, pentane
Visualise TLC plates using non-destructive method: The TLC plates can be visualized
by placing the plate under UV lamp and circle any UV active spots with a pencil. The
plate can also be stained with iodine.
Materials:
3 leaves 1 stirring rod 1 glass teat pipette
TLC plate 1 watch glass 1 x 250 ml beaker
mortar and pestle capillary/spotting tubes test-tube
Extraction Solvent : 88%: 12% mixture of acetone: petroleum ether
Running Solvent : mixture of 100ml petroleum ether, 11ml 2-propanol and 5 drops of
distilled water.
Procedure:
Extraction of Pigment
1. Place 3 leaves and one spatula of sand into a mortar.
2. Crush the leaves with the help of a pestle.
3. Transfer the crushed leaves into a clean test-tube and add extraction solvent just
enough to cover the leaves.
4. Add half spatula of anhydrous Sodium Sulfate and cover the test-tube mouth with
aluminium foil.
5. Shake the test-tube well and leave it for about 15 minutes.

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Preparation of TLC Chamber (in the fume cupboard)
6. Add running solvent to completely cover the beaker to a depth of approximately
0.5cm.
7. Cover the beaker with aluminium foil and give a gentle shake. Keep the chamber
covered so that evaporation does not change the solvent composition. The chamber
will be saturated with vapor in about 15 minutes.