Validation of an automated liquid chromatographic method for omeprazole in human plasma using on-line solid-phase extraction

An automated system using on-line solid-phase extraction and HPLC with UV detection has been validated in order to determine omeprazole in human plasma. The extraction was carried out using C18 cartridges. After washing, omeprazole was eluted from the cartridge with mobile phase onto an Inertsil ODS-2 column. The developed method was selective and linear for drug concentrations ranging between 5 and 500 ng ml(-1). The recovery of omeprazole ranged from 88.1 to 101.5%, and the limit of quantitation (LOQ) was 5 ng ml(-1). The intraday accuracy ranged from 93.1 to 106.2% and the interday accuracy varied from 95.4 to 105.1%. For the LOQ, good values of precision (8.7 and 17.5% for intraday and interday, respectively) were also obtained. This automated system has been applied to determine omeprazole in human plasma samples from bioequivalence studies.