Application of heart-cutting two-dimensional liquid chromatography-mass spectrometry to the characterization of highly polar impurities in calcium gluconate injection

•A heart-cutting IPRP-HILIC-MS system with a make-up flow was developed.•The interface conditions were optimized to achieve good peak shape and peak intensity of highly polar impurities.•Five impurities were separated and identified, four of them were confirmed by reference substances.