Kinetic investigation on the degradation of lorazepam in acidic aqueous solutions by high performance liquid chromatography

A high performance liquid chromatographic method was developed for the kinetic investigation on the acidic hydrolysis of lorazepam in 0.01, 0.1, and 1.0 M hydrochloric acid solutions. In this study, the simultaneous determination of lorazepam and its main degradation product was performed on a reversed phase BDS C-8 column. The mobile phase consisted of a mixture of methanol : acetonitrile : buffer solution containing 0.005 M KH2PO4 and 0.1 M CH3COONH4 adjusted to pH 6.0 with glacial acetic acid (35 : 20 : 45, v/v/v) pumped at a flow rate of 1.5 mL/min. The UV detector was operated at 230 nm. The main degradation product attained under the above mentioned experimental conditions was 6-chloro-4-(2-chlorophenyl)-2-quinazolinecarboxaldehyde which was isolated and identified by H-1-, C-13-NMR and mass spectrometry. The proposed method showed a relative standard deviation of less than 2.04 % and detection limits of 0.16 and 0.17 mu g/mL for lorazepam and its main degradation product, respectively.