Results and Discussion
The Color Reaction of Flavonoids and Chromogenic
System
The basic structure of flavonoids was presented in Fig. 2a,
and most of the flavonoids in P. oleracea L. have 3′,4′-
dihydroxy-substituted structure (as shown in Fig. 2b).
Flavonoids with 3′,4′-dihydroxy-substituted structure can
show special color by reacting with the system of NaNO2–
Al(NO3)3–NaOH. The color reaction of flavonoids and
chromogenic system is presented in Fig. 2c. As shown in
Fig. 2, this method is based on the reaction of aluminum
ion with flavonoid at alkaline medium forming red chelates.
By measuring the absorption of such red chelates, it is
possible to determine the flavonoids.
Selection of Detective Wavelength
Ultraviolet scanning (presented in Fig. 3) was performed to
determine the detective wavelength. The solution of rutin
and the solution of sample were prepared (as the description
in determination of flavonoids). From Fig. 3, we can see
that both rutin and sample showed maximum absorption at
the wavelength of 500 nm in visible range, so the
wavelength of 500 nm can be selected for detection of
target analyte.
Comparison of Extraction Efficiency with Different
Solvents
The extraction of the three mentioned solvents was
investigated with microwave-assisted extraction, including
Fig. 3