Effect of various salts on the stability of lansoprazole, omeprazole, and pantoprazole as determined by high-performance liquid chromatography

A fast and reproducible reverse-phase high-performance liquid chromatography (HPLC) assay method has been developed for the simultaneous quantitation of omeprazole, lansoprazole, and pantoprazole. The three compounds were monitored at 280 nm using Zorbax Eclipse XDB C-8 (5 mu m, 250 cm x 4.6 mm i.d.) and a mobile phase consisting of 700:300 phosphate buffer: acetonitrile with the pH adjusted to 7.0 with phosphoric acid. The method was used to study the effect of pH and various salts on the stability of the three compounds. The pH rate profile curve showed that pantoprazole was the most stable compound and lansoprazole the least stable. The stabilities of the compounds in salt solutions were found to be in the following order: phosphate buffer < trisodium citrate < citrate buffer less than or equal to acetate buffer < citric acid less than or equal to monosodium citrate less than or equal to calcium carbonate < sodium bicarbonate < sodium chloride < water. The rate of degradation had a direct relationship with the H+ and salt concentration.