|MadSci Network: Botany|
Where did you get the idea to use acetone and petroleum ether (1:9) solvent? If you have a reference recommending that solvent, it might have some Rf values. Rf values will be unique for each solvent. However, the general order of the Rf values should be the same because the more nonpolar pigments move farther in nonpolar organic solvents. A recent plant physiology manual (Reiss 1994) identifies six pigments from spinach leaves extracted with hexane and chromatographed with petroleum ether- acetone-chloroform (3:1:1) on silica-gl chromatography. The pigments and their Rf's were: carotene - 0.98 chlorophyll a - 0.59 chlorophyll b - 0.42 pheophytin - 0.81 xanthophyll 1 - 0.28 xanthophyll 2 - 0.15 The color of the bands can be a general guide to identify the pigments. Carotene is orange. Chorophylls are green. Chlorophyll a is a blue-green. Chlorophyll b is a yellow-green. Xanthophylls are yellow. Phaeophytin is chlorophyll lacking the central magnesium ion. Pheophytin is an olive-green. Chlorophyll exposed to acid will be converted to pheophytin. Calcium carbonate is usually added during the leaf extraction process to prevent chlorophyll from degrading to pheophytin. You can differentiate phaeophytin from chlorophyll because it has weaker fluorescence in a fluorimeter. The geranium leaf might contain an additional carotenoid or xanthophyll. The two bands visible under UV light would technically not be pigments because pigments reflect some visible light and appear colored to the human eye, hence the term "chroma" (color) in chromatography. Geranium leaves often contain oils so maybe they represent the two nonvisible bands. References Reiss, Carol 1994. Experiments in Plant Physiology. Englewood Cliffs, NJ: Prentice Hall. Measuring Phaeophytin and Chlorophyll by Fluorescence New Crops Potential of Queensland-grown Geranium (Pelargonium hybrid) for Essential Oil
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