Science Home Page

Chromatography & Plant Pigments



Discussion:

During photosynthesis chloroplasts function to create food (the sugar glucose) for plants  The process involves using light energy, carbon dioxide and water to create glucose and release oxygen.

6CO2 + H20---> C6H12O6 +  6O2

 

The green color comes from the pigment chlorophyll a & b. There are other pigments called carotenes and xanthophylls. However the best pigment for catching light energy is chlorophyll.

 

Chromatography is a method of separating material by dissolving it in a solvent.

Solvent: something that dissolves material

Solute: The material that is dissolved.

In chromatography the solute is placed on a piece of filter paper. The paper is put in a  a chromatography chamber which can be a beaker or a small glass. The bottom of the chamber is filled with a solute, in this case isopropyl alcohol or acetone. The solvent will climb up the paper because of wick action. As the solvent climbs passed the solute it will dissolve the material and carry it along. As the solvent continues to climb up the paper various components of the solute will be deposited on the paper at different points. The components are carried along at different rates because they are not equally soluble in water and are attracted in various degrees to the paper. Chromatography can be used to separate the components of almost any material that is soluble in a solvent. 

Try using washable markers to create chromatography art work.

Chloroplasts contain a variety of pigments that function in photosynthesis. The green chlorophyll hides some of these pigments. This experiment  will separate these pigments using paper chromatograph.

Materials

§ 1 green leaf

§ 1 red leaf

§ A penny

§ 2 pieces of filter paper (coffee filters work too)

§ 1 chromatography chamber

§ Isopropyl alcohol (rubbing alcohol)

§ Acetone (nail polish remover)

§ Metric ruler

§ Pencil

Procedure

1). Take a filter paper strip. Using a pencil draw a base line 1.5 cm from the bottom of the strip.

2). Place the leaf over the pencil line. Roll the penny over the leaf along the pencil line. Make sure that you have rolled the penny until you have a green line horizontal to the pencil line.

3). Add just enough isopropyl alcohol to the chromatography chamber to cover the bottom. Do not add more than one centimeter.

4). Place the filter paper in the chamber with the pencil line down.

The solvent will begin to move up the paper and cause the pigments to move as well.

5). Cover the chamber to prevent evaporation. Do not disturb the chamber until the solvent is about 1 cm from the top of the filter paper.

6). Remove the paper and mark the solvents furthest point with a pencil and allow the strip to dry.

7). Repeat with different type of leaves.

8). The colors you should observe will include

Faint yellow - carotenes

Yellow – xanthophylls

Bright green- chlorophyll a

Yellow green – chlorophyll b

Red – anthocyanin