Abstract: OBJECTIVE To study the unknown impurity in potassium aspartate and magnesium aspartate injection by heart-cutting two-dimensional liquid chromatography coupled with Quadrupole time-of-flight mass spectrometry (2D-LC-Q-TOF-MS). METHODS The Waters ACQUITY UPLC 2D system and Xevo G2-XS QTof-MS system were used. One- dimensional chromatographic conditions were as listed. An Agilent ZORBAX-NH2 column was used, and potassium dihydrogen thophosphate(0.05 mol·L^-1)-acetonitrile(37∶63) as the mobile phase, at a flow rate of 1.3 mL·min^-1. The detection wavelength was set at 200 nm. Two-dimensional chromatographic conditions were as listed. A Waters ACQUITY UPLC HSS T3 column was used, and 0.1% formic acid solution(ESI⁺)/5 mmol·L^-1 ammonium formate(ESI^-) as the mobile phase A, and acetonitrile as the mobile phase B, in gradient mode. The mass spectrometry used an electro spray ionization source(ESI) for positive and negative ion mode detection. RESULTS Combined the high resolution mass, MS² fragment ions and the UNIFI software, the possible structure of the unknown impurity in potassium aspartate and magnesium aspartate injection was infered. CONCLUSION The 2D-LC-Q-TOF-MS method can be used to identify impurities in potassium aspartate and magnesium aspartate injection, which provides reference for the improvement of quality control and process optimization of potassium aspartate and magnesium aspartate injection.