Determination of omeprazole, hydroxyomeprazole and omeprazole sulfone using automated solid phase extraction and micellar electrokinetic capillary chromatography

A sensitive method for the determination of omeprazole and its metabolites has been developed. It involves an automated solid phase extraction (SPE) procedure and capillary electrophoresis with UV detection. Omeprazole, hydroxyomeprazole and omeprazole sulfone could be separated by micellar electrokinetic capillary chromatography using a background electrolyte composed of 20 mM borate buffer and 30 mM sodium dodecyl sulfate, pH 9.5. The isolation of omeprazole and its metabolites from plasma was automatically accomplished with an original SPE procedure using surface-modified styrene–divinylbenzene polymer cartridges. Good recovery data and satisfactory precision values were obtained. Responses were linear for the three analytes, from 0.08 to 2.0 μg/mL of plasma. Intra- and inter-day precision values of about 1.6% R.S.D. (n = 10) and 2.5% R.S.D. (n = 36), respectively, were obtained. The method is highly robust and no breakdown of the current or capillary blockages were observed during several weeks of operation. The validated method was applied to the determination of omeprazole in pharmaceutical preparations and for the analysis of plasma samples obtained from three volunteers who received oral doses of omeprazole.