A new high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS) was developed for quantitative analysis of atractylenolide I in rat plasma using buspirone as internal standard (I.S.). Rat plasma samples were deproteined with methanol and acetonitrile (1:1, v/v). Atractylenolide I and I.S. were separated on a Phenomenex Gemini C(18) column (50 mm × 2.0 mm, 5 μm) with gradient mobile phase at the flow rate of 0.4 ml/min. The detection was performed by positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode. The linear calibration curve of atractylenolide I in rat plasma ranged 2.0-5000 ng/ml (R>0.9979). The limit of detection (LOD) and the limit of quantification (LOQ) were 0.6 ng/ml and 2.0 ng/ml, respectively. Both accuracy and precision of the assay were satisfactory. The recoveries of atractylenolide I and I.S. were 91.4% and 87.8%, respectively. This fully validated method was applied to a pharmacokinetic study of atractylenolide I in rats administered with 20 g/kg Atractylodis extract. The main pharmacokinetic parameters T(max) (the time to peak), C(max) (the concentration to peak), T(0.5) (the biological half time), and K(e) (the elimination rate constant) were 0.81 ± 0.11h, 7.99 ± 1.2 ng/ml, 1.94 ± 0.27 h, 0.365 ± 0.06/h, respectively.
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