PICOGRAM DETERMINATION OF FINASTERIDE IN HUMAN PLASMA AND SEMEN BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION TANDEM MASS-SPECTROMETRY

A method based on high-performance liquid chromatography (HPLC) with a tmospheric-pressure positive-ion chemical ionization (APCI)-tandem mas s spectrometric (MS-MS) detection for the determination of finasteride (MK-906, I) in human plasma and semen has been developed. The drug an d internal standard (II) were extracted from biological matrices using a single solid-phase cyano cartridge. The eluent from the cartridge w as injected directly onto the a 33 x 4.6 mm I.D. C-18, 3-mu m column c oupled with a base deactivated C-18 20 x 4.6 mm I.D., 5-mu m guard col umn. The column eluate was passed into the corona discharge APCI sourc e by means of a heated nebulizer interface. The analyte and its intern al standard were detected using multiple reaction monitoring (MRM) mod e for enhanced selectivity and sensitivity. The chromatographic run ti me was 3 min, and the method had sufficient sensitivity, precision, ac curacy and selectivity for the analysis of clinical samples containing finasteride at concentration of 0.2 ng/ml. The assay methodology conf irms the versatility of APCI-MS-MS detection, combined with HPLC, for the quantitation of selected drugs in the sub-ng/ml range in biologica l fluids.