Abstract
Adsorption on cellulose using a batch procedure seems to be suitable for the separation of an excess of free quercetin from copper-complexed species in synthetic solutions and in an aqueous methanolic onion extract. Liquid/liquid extraction with chloroform is also suitable for separating free flavonoids from metal/flavonoid complexes. With gel-permeation chromatography, it is possible to fractionate the flavonoids in plant extracts without changing the chemical speciation. Determination of copper concentrations in the fractions, and ultraviolet/visible spectrophotometric studies of the flavonoids with shift reagents, provide information on the presence and type of the copper/flavonoid species in vegetables such as onions and tomatoes.
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