Determination of (R)- and (S)-phenprocoumon in human plasma by enantioselective liquid chromatography/electrospray ionisation tandem mass spectrometry

Phenprocoumon is a commonly used oral anticoagulant of the coumarin type, and has found extensive clinical use in the treatment of thrombophlebitis, pulmonary embolism and atrial fibrillation. In the course of a clinical study to investigate the influence of genetic polymorphisms of the CYP2C9 enzyme on phenprocoumon metabolism, we developed a new enantioselective liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/MS/MS) method to quantify (R)‐ and (S)‐phenprocoumon in human plasma. HPLC separation of the enantiomers was achieved on a Chira‐Grom‐2 column under isocratic conditions using a water/acetonitrile/formic acid eluent. For detection and quantification a triple‐quadrupole MS system was used in the selected reaction monitoring (SRM) mode. As an internal standard the structurally homologous compound warfarin was chosen. The detector response was linear with a correlation coefficient of 0.988–0.999 for (R)‐phenprocoumon and 0.989–0.999 for (S)‐phenprocoumon in the investigated concentration range between 62.5 and 1000 ng/mL (per enantiomer). The limit of detection (LOD) was 12.5 ng/mL. Copyright © 2004 John Wiley & Sons, Ltd.