SIMULTANEOUS DETERMINATION OF NORETHISTERONE AND 6 METABOLITES IN HUMAN PLASMA BY CAPILLARY GAS-CHROMATOGRAPHY WITH MASS-SELECTIVE DETECTION

A method for the simultaneous determination of norethisterone (NET) an d six metabolites in human plasma by capillary gas chromatography-mass -selective detection (GC-MS) is described. The compounds are determine d in plasma after enzymatic hydrolysis. After addition of norgestrel a s the internal standard, the compounds are extracted from plasma at pH 5 using an Extrelut column and elution with dichloromethane. After ev aporation, the compounds are converted into bistrimethylsilyl derivati ves which are determined by gas chromatography using a mass-selective detector at m/z 429 for the two dihydro-NET (5 beta-NET and 5 alpha-NE T), m/z 431 for the four tetrahydro-NET (3 alpha,5 alpha-NET, 3 alpha, 5 beta-NET, 3 beta,5 beta-NET and 3 beta 5 alpha-NET), m/z 442 for NET and m/z 456 for the internal standard. The reproducibility and accura cy of the method were found suitable over the range of concentrations between 0.50 and 8 ng/ml for NET, and metabolites except for 5 alpha-d ihydro-NET (between 1 and 8 ng/ml). The method was applied to clinical samples.