Pigments in a leaf
During Autumn, the suburbs turn on a beautiful display of colour. Just prior to dropping their leaves for the winter trees exhibit wonderful colour changes as the leaves change from green to shades of red, orange and yellow. Where do this pigments come from. Does the plant destroy the green pigment and create the red, orange and yellow pigments? Is the red pigment present in the green leaves? How many pigments are present in the leaves.
To answer some of the questions above we need to separate the pigments from each leaf. So we collect samples of green and red leaves from the same plant. In this case we used an Elm tree.
We crush the leaf with sand using a mortar and pestle. We also add several drops of methylated spirits.
Using the end of an eye dropper suck up the pigment and place a small drop onto the chromatography paper as shown on the right.
The solvent drags the pigment mixture through the chromatography paper. As the pigment mixture rises the constituent pigments are separated according to size, solubility in the solvent and their attraction to the chromatography paper.
Using a different chromatography solvent produces slightly different results. Here the solvent consisted of 90% by volume of petroleum ether and 10% by volume acetone. Clearly shown are the different pigments in the leaf namely the carotenes (orange) at the very top, xanthophylls (yellow) chlorophyll-a (yellow-green), chlorophyll-b (blue-green) and anthocyanin (red).
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