Lab Report: Isolation of Plant Pigments
The presence of different pigment molecules in the leaves of plants is due to the presence of carotenoids and chlorophyll. These pigments are of different colors such as red, green, yellow and orange. Separation of these different colors involves the application of three different processes namely solvent extraction, chromatography and spectrophotometry. Solvent extraction is used to extract these pigments from the leaves, chromatography applied to separate the extracted pigments. Finally, spectrophotometry is used to identify the different colors separated by chromatography. These three different processes follow each other in succession, and must be done with accuracy and precision. The most common plant pigment is chlorophyll that is green in color. On the other hand, carotenoids because of their oxygen component may be orange, red or yellow in color. Chlorophyll absorbs light at 450 nm and 650-700 nm in the blue and red wavelength regions. In the paper chromatogram, there will be different regions representing the different pigments. Beta carotene appears as yellow-orange, pheophytin as grey, chlorophyll a as blue-green, chlorophyll b as green and xanthophylls as yellow. There are also other pigments called the anthrocyanins that appear reddish in color.
All these pigments absorb light at different wavelengths and resolute on the paper chromatogram at different speeds. As a result, they will occupy different regions on the paper chromatogram based on their resolution. A look at the results of the paper chromatography reveals a chromatogram with five different regions occupied by different pigments. We observe an orange pigment, yellow pigment, yellow-green pigment, blue-green and reddish pigments in that order. These are the pigments that are clearly visible on the chromatogram. These pigments appear in this order from the solvent front. Remember the solvent used in this process must not dissolve any of these pigments. There are other pigments in blurred and appear grey in color. They appear at the bottom of the rest of the pigments. Continue Reading »