Characterization of impurities in the bulk drug lisinopril by liquid chromatography/ion trap spectrometry

Two trace impurities in the bulk drug lisinopril were detected by means of high-performance liquid chromatography coupled with mass spectrometry （HPLC/MS） with a simple and sensitive method suitable for HPLC/MSn analysis. The fragmentation behavior of lisinopfil and the impurities was investigated, and two unknown impurities were elucidated as 2-（6-amino- l-（l-carboxyethylamino）- l-oxohexan-2-ylamino）-4-phenylbutanoic acid and 6-amino-2-（l-carboxy-3-phenylpropylamino）-hexanoic acid on the basis of the multi-stage mass spectrometry and exact mass evidence, The proposed structures of the two unknown impurities were further confirmed by nuclear magnetic resonance （NMR） experiments after preparative isolation.