A liquid chromatography-electrospray ionization-mass spectrometry （LC-ESI-MS） method was developed for the determination of montelukast in human plasma. After precipitation of plasma proteins, the plasma samples were separated on a C18 column with a mobile phase consisted of 20 mmol/L ammonium acetate buffer solution containing 0.2% formic acid-methanol （12：88, v/v）. LC-ESI-MS was performed in the selected-ion monitoring （SIM） mode using target ions [M＋H]^＋ at m/z 586.2 for montelukast and m/z 515.2 for telmisartan, the internal standard （IS）. The calibration curve was linear over the plasma concentration range of 1 ng/mL-1000 ng/mL. The lower limit of quantification （LLOQ） was 1 ng/mL for montelukast. The relative standard deviations ofintra- and inter-batches were less than 5.9% and 10.0%, respectively. The method was successfully applied to study the pharmacokinetics of montelukast sodium tablets in healthy Chinese volunteers.
