This paper provides chemical information of controlled degradation processes on omeprazole, and its main degradation products in aqueous solutions, using CE as the analytical technique. Both diode-array and ESI-IT-MS were employed as detectors in order to generate analytical data of the drugs studied. This information could be used to determine potential impurities for pharmaceuticals of omeprazole because it may influence not only the therapeutic efficacy but also the safety of active pharmaceutical ingredients. For this purpose, a new capillary zone electrophoresis method using diode-array detection for the simultaneous determination of omeprazole and its main degradation products was developed. Some different less aggressive degradation processes were studied, the fastest of which was found to be that of omeprazole in aqueous solutions exposed to UV light (254 nm). Using a background electrolyte (10 mM phosphate buffer, pH 12) the analytes were determined in less than 6 min. Electrophoretic behaviour using an optical detector revealed the presence of seven products under the different experimental conditions used. More analytical chemical information was obtained on omeprazole degradation products using direct infusion electrospray ionization-mass spectrometry operating in negative ion mode [M − H]⁻, and even some chemical structures of omeprazole degradation products have been proposed.