Identification of Monomethyl Sulfate and Sulfate Impurities in Zidebactam Using LC–MS and Application of Mixed-Mode Liquid Chromatography with Charged Aerosol Detection and Ion Chromatography for Quantification

Zidebactam (ZID), a novel β-lactam enhancer drug being developed to treat infections caused by Gram-negative bacteria, currently is in phase III clinical development. Two ionic impurities observed in liquid chromatography with charged aerosol detector (CAD) analysis were identified through liquid-chromatography mass spectrometry (LC–MS) as sulfate (SO 4 −2 ) and monomethyl sulfate (CH 3 OSO 3 −1 , MMS). There genesis was attributed to the use of pyridine sulfur trioxide as a reagent in ZID synthesis. A new chromatographic method using mixed-mode stationary phase and CAD was developed and validated. The separation of ionic impurities was achieved on Obelisc-N column using buffer gradient. The new method was found to be simple, specific, sensitive, precise, accurate and robust for controlling these impurities in new drug substance. Accuracy of the method was verified by comparing the results with that of ion chromatography (IC) with conductivity detector. The IC method was employed to monitor the impurities in ZID drug substance used for clinical trials and stability analysis. Graphic abstract