Determinations of morin, quercetin and their conjugate metabolites in serum.

Morin and quercetin are isomeric antioxidant flavonols. High-performance liquid chromatographic methods were developed for the quantitation of morin and quercetin in serum. The method employed a Cosmosil RP-18 column, using acetonitrile/0.2% o-phosphoric acid 28/72 and 27/73 (v/v) as mobile phases, with ethyl paraben and 6,7-dimethoxycoumarin used as internal standards for morin and quercetin, respectively. Moreover, a strategy to stabilize morin/quercetin released from their glucuronides/sulfates in serum during hydrolysis was established. The present methods are applicable for determining morin, quercetin, and their glucuronides/sulfates in serum.