Stereoselective determination of citalopram and desmethylcitalopram in human plasma and breast milk by liquid chromatography tandem mass spectrometry

Abstract

A high performance liquid chromatography (HPLC) tandem mass spectrometry (MS/MS) method was developed for the simultaneous, stereoselective quantification of the antidepressant citalopram and its active metabolite desmethylcitalopram in human plasma and breast milk. Sample preparation was performed by a two-step approach, including generic protein precipitation with acetonitrile followed by solid phase extraction. Enantiospecific separation of analytes was achieved on a Phenomenex® Lux Cellulose-2 column (4.6mm×150mm; 5μm), using reversed phase chromatography conditions characterized by a gradient elution of ammonium acetate buffer (pH 9.0; 20mM) and acetonitrile at a flow rate of 0.6ml/min. The compounds were detected by a tandem quadrupole mass spectrometer equipped with an electrospray ionization source and operating in multiple reaction monitoring mode. The method was fully validated in both biological fluids over a large concentration range of 0.1–100ng/ml for S-(+)- and R-(−)-citalopram, and 0.3–100ng/ml for S-(+)- and R-(−)-desmethylcitalopram. Trueness (90.0–113.3% and 97.1–103.6%), repeatability (0.9–15.9% and 0.9–8.4%) and intermediate precision (1.3–17.8% and 0.9–9.6%) in plasma and breast milk, respectively, meet international guidelines for method validation. Internal standard-normalized matrix effects ranged between 99 and 101% and 98–105%, respectively. The accuracy profiles (total error of trueness and precision) were mostly within the acceptance limits for biological samples defined as ±30%. The method was successfully applied to patient samples in a clinical trial setting.