Determination of cymipristone in human plasma by liquid chromatography-electrospray ionization-tandem mass spectrometry.

A rapid, specific and sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry method was developed and validated for determination of cymipristone in human plasma. Mifepristone was used as the internal standard (IS). Plasma samples were deproteinized using methanol. The compounds were separated on a ZORBAX SB C(18) column (50 mm x 2.1 mm i.d., dp 1.8 microm) with gradient elution at a flow-rate of 0.3 ml/min. The mobile phase consisted of 10 mM ammonium acetate and acetonitrile. The detection was performed on a triple-quadruple tandem mass spectrometer by selective reaction monitoring (SRM) mode via electrospray ionization. Target ions were monitored at M+Hm/z 498-->416 and 430-->372 in positive electrospray ionization (ESI) mode for cymipristone and IS, respectively. Linearity was established for the range of concentrations 0.5-100 ng/ml with a coefficient correlation (r) of 0.9996. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.5 ng/ml. The validated method was successfully applied to study the pharmacokinetics of cymipristone in healthy Chinese female subjects.