Determination of isocorynoxeine in rat plasma by liquid chromatography mass spectrometry and its application.

A sensitive and selective liquid chromatography mass spectrometry (LC-MS) method for determination of isocorynoxeine in rat plasma was developed. After addition of midazolam as internal standard (IS), sample preparation was performed by using liquid-liquid extraction with ethyl acetate. Chromatographic separation was achieved on a Zorbax SB-C18 (2.1 mm × 150 mm, 5 µm) column with acetonitrile-0.1% formic acid as mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used to quantify using target fragment ions m/z 383 for isocorynoxeine and m/z 326 for the IS. Calibration plots were linear over the range of 5-500 ng/mL for isocorynoxeine in plasma. Lower limit of quantification (LLOQ) for isocorynoxeine was 5 ng/mL. Mean recovery of isocorynoxeine from plasma was in the range of 93.6-96.6%. CV of intra-day and inter-day precision were both less than 15%. The newly developed method is simple, sensitive, and could function effectively in pharmacokinetic characterization of isocorynoxeine in rat plasma.