Enantiomeric separation and quantification of citalopram in serum by ultra-high performance supercritical fluid chromatography-tandem mass spectrometry

A method for enantiomeric separation and quantification of R/S-citalopram in serum was developed and validated using ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS). Sample preparation prior to UHPSFC-MS/MS analysis consisted of protein precipitation with acidic acetonitrile and filtration through a phospholipid removal plate. The UHPSFC-MS/MS method used an UPC2 Trefoil CEL2 column with a mobile phase consisting of CO2 and methanol/acetonitrile (70:30, v/v) with 10 mM ammonium acetate. The injection volume was 1 μL and run time was 4 min. MS/MS detection was performed with positive electrospray ionization and two multiple reaction monitoring transitions (m/z 325.1 > 262.0 and m/z 325.1 > 109.0). The calibration range was 5–500 nM for each analyte. The between-assay relative standard deviations were in the range of 3.4–4.5%. Recovery was 81–91% and matrix effects ranged from 96 to 101% (corrected with internal standard). After development and initial testing, the method has been successfully implemented in routine use in our laboratory for both separation and quantification of R/S-citalopram in more than 250 serum samples for therapeutic drug monitoring