Liquid chromatography-mass spectrometry method for the determination of amlodipine in human plasma and its application in a bioequivalence study.

A sensitive and selective liquid chromatographic-mass spectrometric (LC-MS) method for the determination of amlodipine (CAS 88150-42-9) in human plasma has been developed. Sample preparation was based on liquid-liquid extraction using NaOH and cyclohexane. Analytical determination was carried out on a C18 column interfaced with a single quadrupole mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase was 10 mmol/L ammonium acetate solution-methanol (30:70, v/v) at the flow rate of 0.2 mL/min. The method was linear in the concentration range of 0.2-20 ng/mL. The lower limit of quantification was 0.2 ng/mL. Amlodipine was sensitive to UV light. The method was validated in terms of accuracy, precision, absolute recovery, and stability. The intra- and interday relative standard deviation across three validation runs over the entire concentration range was less than 8.17%. The accuracy determined at three concentrations (0.4, 2.0 and 10 ng/mL for amlodipine maleate) was within +/- 3.17% in terms of relative error. The method herein described was successfully applied for the evaluation of pharmacokinetic profiles of amlodipine maleate tablets in 20 healthy volunteers. The results showed that AUC, Tmax, Cmax and T 1/2 between the test and reference formulation have no significant difference (P > 0.05). The relative bioavailability was 103.7 +/- 12.3%.