Liquid chromatography–positive ion electrospray mass spectrometry method for the quantification of citalopram in human plasma

A rapid, sensitive and novel narrow-bore liquid chromatography–mass spectrometric method was developed and fully validated for the quantification of citalopram in human plasma. The analyte and internal standard (imipramine) were extracted by liquid–liquid extraction with a mixture of hexane–heptane–isopropanol (88:10:2, v/v/v). The use of a Hypersil BDS C8 micro-bore column (250 mm × 2.1 mm i.d.; 3.5 μm particle size), results in substantial reduction in solvent consumption. The mobile phase consisted of 10 mM ammonium formate–formic acid (pH 4.5) and acetonitrile (30:70, v/v), pumped at a flow rate of 0.15 ml min−1. The analytes were detected after positive electrospray ionization using the selected ion-monitoring mode of the species at m/z 325 for citalopram and m/z 281 for imipramine. The method had a chromatographic run time of 10.0 min and a linear calibration curve over the range 0.50–250 ng ml−1 (r2 > 0.996). The limit of quantitation was 0.50 ng ml−1. Accuracy and precision were below the acceptance limits of 15%.