Figure 1.
Variations of optical densities of quercetin solution at wavelength 294 ± 2 nm in result of its slow stepwise titration by NaOH within the pH range 6-10. The anomaly at pH 7.2-7.1 is caused by the interruption of the process for ca. 30 min; the second one (at pH 8.2-7.7) was obtained after the storage of the solution during one week.