In this experiment, pigments were isolated at first, and observed by using thin-layer chromatography. During extraction, petrol ether, acetone and calcium carbonate were added to spinach leaves and grinded together by using mortar and pestle. Because pigments only dissolve in organic solvent but some impurities such as flesh and fiber dissolve in inorganic solvent, aqueous sodium chloride and petrol ether were added to purify the extract. By using thin-layer chromatography, pigment fractions showed on the TLC silica gel plate. The solubility of different pigments in solvent was found out through calculating the Rf values of different pigment fractions. The results showed that yellow pigment has the smallest solubility strength in mobile phase; the olive green color has the biggest solubility strength. Golden pigment which should have the bigger solubility than olive green pigment, had the smaller absorption strength than olive green pigment in this experiment; the error will be discussed later.
The colored in plants are usually fall in two major categories: carotenoid and chlorophylls. β-carotene is golden colored pigment which is non-polar. Chlorophylls contain two types: chlorophyll a and chlorophyll b; chlorophyll a is blue green colored and chlorophyll b is yellow green colored. Different from β-carotene, chlorophyll contain several polar C-O, C-N bonds and magnesium chelated ion to an nitrogen atom thus they has strong polarity. There exist other small amount pigments such as lutein, xanthophylls and pheophytin. Xanthophylls look like chlorophylls but the magnesium ion is replaced by two hydrogen ions.
Pigments isolation depends on different polarities of pigments. During using thin-layer chromatography to separate and purify the pigments, mobile phase and stationary phase are necessary. Mobile phase also called Developing solvent, which consists of several organic chemicals that can be changed. The components of mobile phase... [continues]
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