Omeprazole determination using HPLC with coulometric detection

A sensitive high performance liquid chromatography (HPLC) method for the de termination of omeprazole and three related benzimidazoles is reported. Cou lometric detection was carried out at + 800 mV using a porous carbon electr ode. The linear range is 0.01-10 mug/ml. The method has a high degree of pr ecision; the relative standard deviation of omeprazole at a concentration o f 1.06 mug/ml was 0.7% (n = 4). The cyclic voltammogram of omeprazole is co nsistent with the hydrodynamic voltammogram exhibiting a single major irrev ersible oxidative wave with a peak potential at + 1105 mV. The response fac tors for the four compounds are similar indicating that the oxidative proce ss does not involve the sulfur moiety exclusively. The data are most consis tent with oxidation primarily of the benzimidazole groups. The method was a pplied successfully to the determination of omeprazole in a paste formulati on. (C) 2001 Elsevier Science B.V. All rights reserved.