Separation and characterization of unknown impurities in cefonicid sodium by trap-free two-dimensional liquid chromatography combined with ion trap time-of-flight mass spectrometry.

Abstract

Seven unknown antibiotic impurities in cefonicid sodium were separated and characterized by a trap-free two-dimensional liquid chromatography coupled to high-resolution ion-trap time-of-flight mass spectrometry (2D-LC/IT-TOF MS) using both positive and negative modes of electrospray ionization. Trap-free 2D-LC and an online demineralization technique made it possible to characterize cefonicid sodium under the conditions of the official standard, and the TIC chromatogram obtained by LC/MS was in conformity with the LC chromatogram obtained by the official analytical method in the peak sequence of impurities. In the first dimension, the column was a GRACE Alltima C18 (250mm×4.6mm, 5μm), and the gradient elution used 0.02mol·L-1 ammonium dihydrogen phosphate solution and methanol as mobile phase. In the second dimension, the analytical column was a Shimadzu Shim-pack GISS C18 (50mm×2.1mm, 1.9μm) with 10mmol·L-1 ammonium formate solution and methanol as mobile phase. Full scan LC/MS was first executed to obtain the exact m/z values of the molecules. Then LC/MS2 and LC-MS3 experiments were performed on the compounds of interest. The structures of seven unknown degradation products in cefonicid sodium were deduced based on the high-resolution MSn data using both positive and negative mode. The problem of incompatibility between the non-volatile salt mobile phase and mass spectrometry was solved completely by multidimensional heart-cutting approaches and an online demineralization technique, which is worthy of widespread use and application for the advantages of stability and repeatability.