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Abstract
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 (150 × 3.0 mm, 3 µm. UK) column interfaced with a LTQ Orbitrap mass spectrometer. The calibration range for omeprazole and omeprazole sulphone was 0.002–1 µg/mL, whereas, for 5-hydroxy omeprazole was 0.005–1 µg/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).