International Journal of

An impurity of Ampicillin sodium formed during a gradient reverse phase high performance liquid chromatography (HPLC) analysis of stress stability samples of the drug substance Ampicillin sodium, and the level of this impurity was found at up to 0.9%. This impurity was identified by LC-MS and characterized by (1H NMR, LC/MS/MS, elemental analysis). Based on the spectral data, the impurity was named as, 3-[[(2R,3S)-[3-methoxy-3-N-[2-(thiophen-2-yl)acetamido]]-4-oxoazetidin-2-ylthio]-2(carbamoyloxy)methyl]]-acrylic acids. The structure of this impurity was also established, prepared by isolation and co-injected into HPLC to confirm the retention time. Structural elucidation further confirms the impurity.