The standards used in this work were isolated from other plant
species, such as carrots and green vegetables, by using open column
chromatography (OCC), according to Kimura and Rodriguez-Amaya
(2002), with a glass column of 2.5 25 cm packed with MgO:Hyflosupercel
(1:1), activated for 2 h at 110 C and developed with
petroleum ether containing varying quantities of acetone and ethyl
ether. Concentrations of the standard solutions were determined
through a spectrophotometer (Hitachi, U-1800, Tokyo, Japan) and
corrected according to their purity through HPLC, considering 90%
as minimum purity to be used as standard.