Studies on the metabolism of omeprazole in the rat using liquid chromatography/ionspray mass spectrometry and the isotope cluster technique with [ 34 S] omeprazole

This paper describes the application of the ionspray (pneumatically-assisted electrospray) interface for liquid chromatography (LC) and atmospheric-pressure ionization mass spectrometry (API MS) to samples obtained in a study on the metabolism of omeprazole. In this study [34S]omeprazole was utilized for the stable isotope cluster technique. Over forty metabolites in a sample of partially purified rat urine were resolved by gradient elution LC with ionspray API MS detection, and each of them produced molecular ion 1:1 clusters (MH+ and [MH + 2]+). The chromatographic fidelity of the total-ion current (TIC) was excellent. The endogenous matrix of the sample was quite low, allowing a background-subtracted averaged mass spectrum of the entire TIC trace to produce a 'metabolite mass profile' depicting all the molecular ion 1:1 clusters in the sample. From this mass profile, it was possible to obtain direct information concerning oxygenation and conjugation reactions of the parent compound.