Simultaneous determination of six flavonoids from Paulownia tomentosa flower extract in rat plasma by LC–MS/MS and its application to a pharmacokinetic study

A simple, rapid and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of six components including apigenin, quercetin, apigenin-7-O-β-d-glucoside, quercetin-3-O-β-d-glucoside, 3′-methoxyluteolin-7-O-β-d-glucoside, and tricin-7-O-β-d-glucopyranoside in rat plasma using formononetin as the internal standard (IS). The plasma samples were pretreated by a one-step liquid–liquid extraction with dichloromethane. The chromatographic separation was carried out on a ZORBAX SB-Aq column with a gradient mobile phase consisting of acetonitrile and 2 mM aqueous ammonium acetate. All analytes and IS were quantitated through electrospray ionization in negative ion multiple reaction monitoring mode. The mass transitions were as follows: m/z 269.1 → 117.2 for apigenin, m/z 301.2 → 151.2 for quercetin, m/z 431.3 → 311.2 for apigenin-7-O-β-d-glucoside, m/z 463.2 → 300.2 for quercetin-3-O-β-d-glucoside, m/z 461.3 → 283.1 for 3′-methoxyluteolin-7-O-β-d-glucoside, m/z 491.3 → 313.1 for tricin-7-O-β-d-glucopyranoside, and m/z 267.2 → 252.2 for IS, respectively. All calibration curves exhibited good linearity with correlation coefficient (r) > 0.995. The intra-day and inter-day precisions (RSD) at three QC levels were both less than 14.0% and the accuracies ranged from 89.8% to 113.8%. The extraction recoveries of six compounds ranged from 82.3% to 92.5%. The validated method was successfully applied to pharmacokinetic study of the six components in male rat plasma after oral administration of Paulownia tomentosa flower extract.