A selective and sensitive liquid chromatography tandem with mass spectrometry was developed and validated for accurate determination of monotropein in rat plasma and tissues. All biological samples were prepared by simple protein precipitation method using catalpol as an internal standard. The analyte and internal standard were separated on a C18 analytical column with 2 min of run time, at flow rate of 0.5 ml/min. The detection was performed on a triple-quadrupole tandem mass spectrometer equipped with negative-ion electrospray ionization by selected-reaction monitoring of the transitions at m/z 389→147 for monotropein and m/z 361→169 for the internal standard. The calibration curves for plasma and tissue samples were linear over the concentration range of 4–2000 ng/ml, with a lower limit of quantification of 4 ng/ml. The method was successfully applied to a pharmacokinetic and tissue distribution study of monotropein in rats.
