Development and validation of LC-MS method for the determination of lisinopril in human plasma and its application in...

A rapid, simple, and specific liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method has been developed and validated for the determination of lisinopril in human plasma. Enalaprilat was used as the internal standard (IS). Sample preparation of the serum involved deproteination with methanol twice, repeatedly. Samples were separated using a Thermo Hypersil-HyPURITY C18 reversed-phase column (150 x 2.1 mm i.d., 5 microm). Mobile phase consisted of formic acid solution (pH 2.9)-methanol-acetonitrile (58:25:17, v/v). Lisinopril and its internal standard were measured by electrospray ion source in positive selected ion monitoring mode. The method was validated with a linear range of 2.5-320 ng/mL and the lowest limits of quantitation were 2.5 ng/mL for lisinopril. The extraction efficiencies were approximately 80% and recoveries of method were in range of 94.4-98.2%. The intra-day relative standard deviation (RSD) was less than 8.8% and inter-day RSD was within 10.3%. QC samples were stable when kept at ambient temperature for 24 h, at -20 degrees C for 30 days and after four freeze/thaw cycles. The method has been successfully applied to the evaluation of pharmacokinetics and bioequivalence of 2 lisinopril formulations in 18 healthy Chinese volunteers after an oral dose of 20 mg.