A selective spectrophotometric method for determination of quercetin in the presence of other flavonoids

A simple, rapid and highly selective method for determination of quercetin in the presence of other flavonoids was developed. The method is based on the oxidation reaction of quercetin in neutral aqueous solution with N-bromosuccinimide (NBS) in the presence of phenol to give a violet chromogen measurable at 510 nm. Beer's law was valid within a concentration range of 2.5-30 mug/ml with a good correlation coefficient (r = 0.9990). All variables were studied to optimize the reaction conditions. The method is highly selective for quercetin. Other investigated flavonoids do not interfere. Mixtures of flavonoids were also analysed through native UV measurements of absorbance readings at 370 nm and then at 510 mn after adopting the proposed procedure. The method could also be utilized for the quantitative determination of quercetin in some plant extracts. Moreover, the proposed procedure could be considered as a good tool to follow the hydrolysis of quercetin glycosides.