A sensitive and selective LC-MS/MS method for determination of citalopram in human plasma was established to study the bioequivalence of different formulations containing citalopram.The samples were simply pretreated by protein precipitation using acetonitrile,and then analyzed on a Zorbax Extend C8 column.The mobile phase consisted of acetonitrile-water-formic acid（60∶40∶0.2）,at a flow-rate of 0.5 mL·min-1.A Thermo Finnigan TSQ Quantum Ultra tandem mass spectrometer equipped with electrospray ionization source was used as detector and was operated in the positive ion mode.Selected reaction monitoring using the precursor to product ion combinations of m/z 325 → m/z 109 and m/z（265 →） m/z 167 was performed to quantify citalopram and the internal standard,respectively.The pharmacokinetic parameters of citalopram in different formulations were calculated by non-compartment model.The linear calibration curves were obtained in the concentration range of 0.10-100 μg·L-1.The lower limit of quantification was 0.10 μg·L-1.The intra-and inter-day relative standard deviation（RSD） over the entire concentration range was less than 5.2%.Accuracy determined at three concentrations(0.25,8.00 and 90.0 μg·L-1 for citalopram) ranged from-4.7% to 1.3%.Each plasma sample was chromatographed within 3.0 min.The method was successfully used in bioequivalence study of citalopram in human plasma after oral administration of 20 mg citalopram.Calculated with AUC0-120 h,the bioavailability of two formulations was（102.1±10.9）%.The method is rapid,selective,robust and is proved to be suitable for bioequivalence evaluation of different formulations containing citalopram.
