Simultaneous Determination of Omeprazole and its Metabolites (5′‐Hydroxyomeprazole and Omeprazole Sulfone) in Human Plasma by Liquid Chromatography‐Tandem Mass Spectrometry

Abstract A method for the simultaneous determination of omeprazole (OME) and its two metabolites (5′‐hydroxyomeprazole (H‐OME) and omeprazole sulfone (OME‐S)) in human plasma is described. OME and its metabolites were extracted from plasma with phosphate buffer (pH 7.4) by using solid phase extraction system, Oasis HLB μ Elution plates, and the eluate was directly injected into LC‐MS/MS system. The analytes were chromatographed with a reversed‐phase column, XTerra MS C18 column (150×4.6 mm) and an HPLC mobile phase which consisted of a mixture of acetonitrile/water (45/55, v/v) containing 10 mM ammonium hydroxide (pH 8.0). A Sciex API 4000 tandem mass spectrometer equipped with a heated nebulizer atmospheric pressure chemical ionization interface was used as a detector and was operated in the positive ion mode. Multiple reaction monitorings using the precursor product ion combinations of m/z 346.2→198.2, 362.0→214.0, 362.0→150.0, and 349.2→201.0 were used to detect OME, H‐OME, OME‐S, and internal standard (OME‐d3), respectively. The method was validated in the concentration range of 1–1000 ng/mL plasma with adequate assay precision, accuracy, and reproducibility. This sensitive and selective method with a rapid and simple sample preparation procedure was applied to a clinical pharmacokinetic study of OME.