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 atmospheric-pressure positive-ion chemical ionization (APCI)-tandem mass spectrometric (MS-MS) detection for the determination of finasteride (MK-906, I) in human plasma and semen has been developed. The drug and internal standard (II) were extracted from biological matrices using a single solid-phase cyano cartridge. The eluent from the cartridge was injected directly onto the a 33 x 4.6 mm I.D. C18, 3-microns column coupled with a base deactivated C18 20 x 4.6 mm I.D., 5-microns guard column. The column eluate was passed into the corona discharge APCI source by means of a heated nebulizer interface. The analyte and its internal standard were detected using multiple reaction monitoring (MRM) mode for enhanced selectivity and sensitivity. The chromatographic run time was 3 min, and the method had sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing finasteride at concentration of 0.2 ng/ml. The assay methodology confirms the versatility of APCI-MS-MS detection, combined with HPLC, for the quantitation of selected drugs in the sub-ng/ml range in biological fluids.