Structural identification of degradants of moexipril by LC-MS/MS

A gradient LC-MS method was developed for the identification and characterization of degradants of moexipril using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Moexipril was subjected to hydrolysis (acid, base and neutral), oxidation, photolytic and thermal degradation conditions as mentioned in ICH guidelines Q1A (R2). The drug degraded under hydrolysis, oxidation and photolytic conditions, but it was stable under thermal conditions. In total, five degradants were formed and separated on an Agilent XDB C-18 column (4.6 × 150 mm, 5 μm) in a gradient elution method. Four degradants (D1, D2, D4 and D5) under acidic conditions, three degradants (D2, D3 and D4) under basic conditions and three degradants (D1, D4 and D5) under neutral and oxidative stress conditions were formed. In addition, two degradants (D4 and D5) were formed under photolytic stress conditions. To elucidate the structures of degradants, fragmentation of moexipril and its degradants was studied using LC-MS/MS experiments and accurate mass measurements (HRMS) data. The fragment ions in the product ion tandem mass spectra of all the degradants were compared with those of moexipril and assigned the probable structures for the degradants.