Determination of the esculetin contents of medicinal plants by liquid chromatography–tandem mass spectrometry

We developed a LC‐MS/MS method for the determination of esculetin contents in medicinal plants. The analysis was performed using multiple reaction monitoring in negative mode, and an XBridge™ C 18 column (2.1 × 100 mm, 3.5 µm) was used. Methanol and 0.1% formic acid were used for gradient analysis. The calibration curve showed good linearity ( r 2  > 0.9993). The limits of detection and quantitation were 0.02 and 0.07 ng/mL, respectively. The intra‐day and inter‐day precisions were 1.5–6.8 and 2.0–5.3%, respectively, and the accuracy was 102.0–110.2%. The contents of esculetin in 35 different plants were determined, and Fraxini Cortex showed the highest content of esculetin (761–5475 mg/kg). In Mori Folium and Artemisiae Capillaris Herba, 5.2–21.5 and 7.0–17.6 mg/kg of esculetin were found, respectively. In other medicinal plants, no esculetin was detected, or it was present at a concentration less than 10 mg/kg. The analysis method appears to be simple, sensitive and reproducible. Contrary to expectations based on traditional medical knowledge, although Artemisiae Capillaris Herba contains a large amount of esculetin, it appears from this study that Fraxini Cortex contains a greater amount. The pharmacological effects of esculetin isolated from medicinal plants should be investigated as part of new medicines development. Copyright © 2012 John Wiley & Sons, Ltd.