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 ammoniumacetate 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, T_max, C_max 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%.