Rapid and sensitive liquid chromatography–tandem mass spectrometry method for the determination of leuprolide in human serum

Leuprolide is a synthetic nonapeptide that has two basic amino acids, arginine and histidine, in its structure. By selection of an appropriate analytical column and optimizing the mobile phase composition, an improved analytical method has been developed and validated to determine leuprolide concentrations in human serum. After methanol-induced protein precipitation of serum samples and Oasis® HLB cartridge solid-phase extraction, leuprolide and an internal standard (alarelin) were analyzed on a C18 column interfaced with a triple quadrupole tandem mass spectrometer with positive electrospray ionization. The mobile phase consisted of acetonitrile–water–propionic acid (20:80:0.05). The analyte and internal standard were both detected in the selective reaction monitoring mode. The method exhibited a linear range of 0.018–45.2 ng/mL for leuprolide. The intra- and inter-assay precisions were 11.5% or less relative standard deviation (R.S.D.), and accuracy was within ±2.8% relative error (RE). The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.018 ng/mL, with acceptable precision and accuracy. The validated LC–MS/MS method was tested to a clinical pharmacokinetic study of leuprolide after a single subcutaneous injection of 1 mg leuprolide acetate in healthy male Chinese volunteers.