Simple and Fast Liquid Chromatography-Mass Spectrometry (LC-MS) Method for the Determination of Omeprazole, 5-hydroxyomeprazole, and Omeprazole Sulphone in Human Plasma

A method was developed for the determination of omeprazole, 5-hydroxy-omeprazole, and omeprazole-sulphone in human plasma. The mobile phase with 0.1% formic acid in acetonitrile and 0.1% formic acid in water (40/60 v/v) was used successfully for the first time for the analysis of these analytes. Analysis was carried out using Hichrom RP18 (150x3.0mm, 3 mu m. UK) column interfaced with a LTQ Orbitrap mass spectrometer. The calibration range for omeprazole and omeprazole sulphone was 0.002-1 mu g/mL, whereas, for 5-hydroxy omeprazole was 0.005-1 mu g/mL. The extracted ion ranges ([M+H](+)) were; m/z 346.12-346.13 for omeprazole, 362.11-362.12 for 5-hydroxy-omeprazole, and omeprazole-sulphone and 384.07-384.09 for pantoprazole. The regression equation for omeprazole was 0.071x+0.445, for 5-hydroxy omeprazole was y=0.08x+0.017 and for omeprazole sulphone y=0.007x+0.05. This method was successfully applied for the determination of pharmacokinetic parameters of omeprazole and its metabolites in human volunteers (n=20).