Lab: Identifying Plant Pigments by Chromatography

Lab: Identifying Plant Pigments by Chromatography

Tessa Czerlau & Grace D’Agostino

Mr.Brgan

28 April 2017

SBI 4U

Question: What types of pigments are found in green leaf extracts from three different species of plants?

        A plant pigment is a type of coloured chemical compound produced by a plant. These compounds absorb and reflect visible light radiation with wavelengths ranging from 380nm-760nm. Plant pigments give color to leaves, flowers, and fruits and are also important in controlling photosynthesis, growth, and development. The selective absorption of wavelengths determines the colour of the pigment. The wavelengths that are not absorbed are reflected and that is the colour seen.There are many different plant pigments found in various species of plants. Chlorophylls absorb red and blue wavelengths, but not green wavelengths, and this gives leaves their characteristic green color. They are used to drive photosynthesis and are the most important plant pigment. Chlorophylls absorb light energy to synthesize carbohydrates which are used to make plant material for growth. Carotenoids are yellow, orange or red pigments found in many plants. They give vegetables like carrots and sweet potatoes their orange colour. One main function of carotenoids are that they transfer some of the light energy they absorb to chlorophyll molecules to use to synthesize carbohydrates. Their second function is to protect plants from overexposure to sunlight. Carotenoids dissipate the excess light energy as heat. Without these pigments the excess light energy could destroy proteins, membranes, and other molecules. (“Plant Pigment”, n.d.) Xanthophylls pigments are yellow and they function similarly to carotenoids. They absorb wavelengths that chlorophyll do not therefore can transfer that energy to synthesize carbohydrates. They also are used in protection of plants by varying the light energy that the plant receives. (Xanthophyll, 2010)

        Chromatography is a way of separating out a mixture of chemicals. The chemicals in a mixture travel at different speeds over a stationary solid due to different solubilities, molar masses and hydrogen bonding with the paper. It is useful in the separation and identification of different plant pigments found in various plant species. Using this technique and the Rf formula, plant pigments can be identified and their properties and roles in photosynthesis can help determine properties of plants.

 Purpose:

        The purpose of this lab was to determine the different pigments found in three different species of plants, using spinach, swiss chard, and purple kale for this experiment.

Hypothesis:

        It was predicted that the plant leaves are different colours because they contain different plant pigments that reflect and absorb different wavelengths of light. Different combinations of plant pigments would result in different colours of plant leaves due to a combination different reflections of wavelengths. It was predicted that there will be more than one plant pigment in the extracts from the three plants. It was predicted that the pigments found in the plant extracts would be different in the three samples. The plants could have had some of the same pigments but different combinations.

Materials:

Safety goggles                                

Three 150-mL test tubes

Laboratory Apron                

Chromatography solvent (90% petroleum ether: 10% acetone, v/v)

Leaves from three different plants (spinach, swiss chard and purple kale)

3 chromatography tubes with cork

Mortar and pestle

Stopper and hook

20 mL of acetone

Scissors

Filter paper

Wax pencil

Capillary tube for spotting

Procedure:

Part I: Extraction of pigments

1. Safety goggles and lab apron were put on.
2. One leaf was ground from each plant separately with a mortar and pestle along with 3 mL of acetone. The mortar and pestle were cleaned with 1 mL of acetone between plants. The specimens were not cross contaminated in any way.
3. 1.5 mL of each sample was transferred to labelled microcentrifuge tubes. The samples were spun at high speed for 1 minute.
4. The supernatant (liquid portion of the mixture) was poured into two clean, labelled 150-mL test tubes, leaving behind the solid pellets of cellular debris.

Part II: Chromatography

      5. 3.0 mL of the chromatography solvent was placed into a chromatography tube with a cork stopper. The tube was kept stoppered while the chromatography paper was prepared.