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A sensitive liquid chromatography tandem mass spectrometry method was developed to quantify amlodipine in human plasma. Alkalinized plasma spiked with desipramine, an internal standard, was extracted by liquid-liquid extraction and evaporated an organic part to dryness. The residue was reconstituted and injected into an Acquity Ultra Performance LC TM , (Waters, Co., Ltd. USA) with C 18 column. The isocratic elution of mobile phase was performed by 90% of acetonitrile and 10% of 10 mM ammonium acetate pH 4 at flow rate of 0.20 mL/min with 5 minutes of total run time. Mass spectrometric analysis was performed using a Quattro Premier XE mass spectrometer, (Micromass Technologies, UK) coupled with an electrospray ionization (ESI) source in the positive ion mode. The MRM transitions of m/z 409.17>238.19 and 409.17>294.09 were selected for amlodipine and 267.09>208.06 for desipramine. The retention times were 1.63 and 1.69 minutes for amlodipine and desipramine, respectively. The linearity of the method revealed a correlation coefficient of >0.998 within the concentration range of 0.05 -20 ng/mL. This work has been fully validated according to the Guidance for Industry: Bioanalytical Method Validation (USFDA CDER, 2001, BP) with high degree of accuracy and precision. This method was applied to quantify amlodipine concentrations in human plasma samples in a bioequivalence study.

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