Leafy Chromatography

    Kids, did you ever wonder about the chemistry of autumn leaf colors? Most plants contain several pigment molecules. If you experiment with different leaves in this activity you will see the wide range of pigments.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

     You will need leaves, baby food jars with lids, rubbing alcohol, coffee filters (preferably the Melitta type), hot water, and a shallow pan. Take 2-3 large leaves (or the equivalent with smaller leaves), tear them into tiny pieces, and place them into small jars with lids. Add enough alcohol to just cover the leaves. Loosely cover the jars and set them into a shallow pan containing an inch or so of hot tap water. Let the jars sit in the hot water for at least a half hour. Replace the hot water as it cools and swirl the jars from time to time. The jars are 'done' when the alcohol has picked up color from the leaves. The darker the color, the brighter the chromatogram will be. Cut a long, thin (1/2”) strip of coffee filter paper for each jar. Place one strip of paper into each jar, with one end in the alcohol and the other outside of the jar. As the alcohol evaporates, it will pull the pigment up the paper, separating pigments according to their molecular size. Pigments with the largest size will move the shortest distance. After 30-90 minutes, remove the strips of paper and allow them to dry. From the information below, can you identify which pigments are present?

    The color of a leaf results from the different pigments produced by the plant. The main pigment classes responsible for leaf color are porphyrins, carotenoids, and flavonoids. The color depends mostly on the amount and types of these pigments. The pigment porphyrin has a compound called chlorophyll that is green. The pigment carotenoid has compounds carotene and lycopene that are yellow , orange , and red , as well as xanthophyll which is yellow. The pigment flavonoid has compounds flavone and flavonol ( yellow ) and anthocyanin that can be red , blue , purple , or magenta.

    When leaves are green, it is because they contain a lot of chlorophyll. Chlorophyll masks all other pigment colors. The anthocyanins will mask carotenoids. As summer turns to autumn, decreasing light levels cause chlorophyll production to slow and the green color will fade. At the same time, anthocyanin production in leaves increases in response to increasing sugar concentrations. Leaves with a lot of anthocyanins will turn red. Leaves with good amounts of both anthocyanins and carotenoids will be orange, and leaves with carotenoids but little or no anthocyanins will turn yellow. In the absence of these pigments, other plant chemicals can affect leaf color. An example is tannins, which cause the brownish color of some oak leaves.

    Options: Does the season in which the leaves are picked affect their colors? Also try using frozen chopped spinach leaves. If your chromatogram is pale, the next time use more leaves and/or smaller pieces.


    Kathleen Carrado Gregar, PhD, Argonne National Labs
    November 2006



    Dr. Anne Marie Helmenstine at and