[Quantification of amlodipine in human plasma by LC-MS/MS method: elimination of matrix effects by improving...

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of amlodipine in human plasma. The influence of alkalizer, extraction solvent and the chromatographic conditions on the matrix effects was investigated. The stable isotope-labeled amlodipine (amlodipine-d(4)) was used as an internal standard. Sample preparation involved simple liquid-liquid extraction procedure using methyl tertiary butyl ether. Chromatographic separation was achieved on a Welch Ultimate XB-C18 (100 mm × 2.1 mm, 3 μm) column with acetonitrile/2 mmol·L(-1) ammonium formate (p H 3.0） under gradient condition at a flow rate of 0.6 m L·min(-1). Detection was performed using electrospray ionization (ESI) in positive ion multiple reaction monitoring (MRM) mode. The linear range of the analyte was 0.1-20.0 μg·L(-1), with the lower limit of quantitation (LLOQ) of 0.1 μg·L(-1). The matrix factor for low, medium, high concentration quality control samples and internal standard was (93.9 ± 1.8)%, (95.8 ± 4.9)%, (93.9 ± 1.5)% and (97.9 ± 5.3)%, respectively. The method showed excellent specificity, linearity, intra-day and inter-day accuracy and precision, extraction recovery and stability, according to the CFDA guidance for bioanalytical method validation. The matrix effect was significantly improved through optimizing the chromatographic conditions. This economical, simple, robust, sensitive and specific method is entirely able to meet the requirement of the determination of amlodipine in human plasma samples obtained from bioequivalence studies.