Determination of Citalopram Enantiomers in Human Plasma with Normal Phase HPLC-MS/MS

A normal phase high performance liquid chromatographytandem mass spectrometry (HPLC-MS/MS) method for the determination of citalopram (CIT) enantiomers concentration in human plasma was established．CHIRALCEL OJ-H column (250 mm×4.6 mm×5 μm) was used. The mobile phase consisted of n-hexane， alcohol and diethylamine (V（n-hexane）∶V（alcohol）∶V（diethylamine）=70∶30∶0.1). The flow rate of mobile phase was 0.5 mL•min^-1. The analytes were determined using atmospheric pressure chemical ionization source and multiple reaction monitoring (MRM) detection mode, which was adopted to detect the concentration of CIT in positive mode. Lidocaine was used as internal standard. CIT and the internal standard are monitored at m/z 325.1→108.9 and m/z 235.4→86.1, respectively. Calibration curves are linear in range from 0.156 to 50 μg•L^-1for rac-CIT, from 0.078 to 25 μg•L^-1 for S-CIT and both the coefficient correlation were more than 0.99. For rac-CIT, S-CIT and R-CIT, the relative recoveries are 99.7%—101.5%, 99.1%—103.3%, 99.9%—100.2%; the extraction recoveries are 73.5%—75.1%, 73.9%—76.0%, 73.1%—74.3%, respectively. The inter-day and intra-day RSDs of the determinations of all species are less than 5.0%.