Lab 10 Activities

Photosynthetic Pigments

Overview

In this activity, you will use chromatography to compare the pigments found in a spinach leaf to the pigments found in spirulina. Spirulina is a powdered dietary supplement made of cyanobacteria from the genus Arthrospira. Both spinach and members of Arthrospira are photosynthetic.

Materials

Each lab group will need the following materials:

• spinach leaf
• chromatography strip
• coin
• chromatography solvent (2 parts isooctane: 1 part acetone: 1 part diethyl ether)
• 1 test tube
• test tube rack
• pencil
• dowel, wooden stirrer, or paperclip
• ruler

Method

Note: Your instructor will prepare and run the chromatography for spirulina.

1. Lay a strip of filter paper on the bench and mark a line with a pencil about 2 cm from the bottom.
2. Place a fresh spinach leaf and rub a coin across the leaf to transfer pigment to the strip along the pencil line.
   • Do not move the spinach leaf along the chromatography strip. Try to keep the pigment on the pencil line.
3. Add about 3 ml of chromatography solvent to the test tube.
4. Suspend the chromatography strip by a dowel or paper clip in the test tube.
   • Make sure the bottom of the strip is in the solvent, but do not allow the spinach pigment to be submerged.
5. Develop the strip until the solvent reaches about 2 cm from the top.
6. Remove the strip from the test tube and quickly mark the solvent front with the pencil.

Chromatography Analysis

Fill in the following table. D_A represents the distance traveled by the pigments. D_S represents the solvent front. Your instructor will provide you with the measurements for the spirulina.

Based on your data, answer the following questions:

1. How many different pigments separate from the spinach extract? From the spirulina?
2. Are all pigments represented between the two extract?
3. The mobile phase is non-polar. Based on this information, what are the properties of each pigment?
4. Measure the R_f of each pigment.

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