Simultaneous determination of five free and total flavonoids in rat plasma by ultra HPLC–MS/MS and its application to a comparative pharmacokinetic study in normal and hyperlipidemic rats

• A uHPLC–MS/MS method was developed for the pharmacokinetic study of Shixiao San.
• Simultaneous determination of five free and total (free and conjugated) flavonoids. The validated method was successfully applied to a comparative pharmacokinetic study.
• The pharmacokinetic profiles in the normal and hyperlipidemic rats were elucidated.

A simple and rapid ultra-high performance liquid chromatography–tandem mass spectrometry (uHPLC–MS/MS) method has been developed for the simultaneous determination of five free flavonoids (amentoflavone, isorhamnetin, naringenin, kaempferol and quercetin) and their total (free and conjugated) forms, and to compare the pharmacokinetics of these active ingredients in normal and hyperlipidemic rats. The free and total forms of these flavonoids were extracted by liquid–liquid extraction with ethyl acetate. The conjugated flavonoids were deconjugated by the enzyme β-Glucuronidase and Sulfatase. Chromatographic separation was accomplished on a ZORBAX Eclipse XDB-C8 USP L7 column using gradient elution. Detection was performed on a 4000Q uHPLC–MS/MS system from AB Sciex using negative ion mode in the multiple reaction monitoring (MRM) mode. The lower limits of quantification were 2.0–5.0 ng/mL for all the analytes. Intra-day and inter-day precision were less than 15% and accuracy ranged from −9.3% to 11.0%, and the mean extraction recoveries of analytes and internal standard (IS) from rat plasma were all more than 81.7%. The validated method was successfully applied to a comparative pharmacokinetic study of five free and total analytes in rat plasma. The results indicated that the absorption of five total flavonoids in hyperlipidemia group were significantly higher than those in normal group with similar concentration–time curves.