Identification and Analysis of Impurities in Erythrosine by High-Performance Liquid Chromatography with Quadrupole Ion Trap Time-of-Flight Mass Spectrometry

A facile method using high-performance liquid chromatography/electrospray ionization quadrupole ion trap time-of-flight mass spectrometry (HPLC-ESI-QIT-TOF/MS) has been established for the analysis of impurities in erythrosine. The mass fragmentation scheme of erythrosine standard was studied systematically, and its fragmentation pathways were concluded. The impurities were separated by HPLC using Shim-pack XR-ODS column (3.0 mm i.d × 75 mm, particle size 2.2 μm) with gradient elution of 0.02 mol L−1 of ammonium acetate buffer solution (pH 4.5) and methanol as mobile phase. Molecular formulas of all impurities were determined by ESI-QIT-TOF/MS via the accurate mass measurement. A total of ten impurities, including seven new impurities, were identified or tentatively characterized with supporting results on the fragmentation pathways of erythrosine standard and accurate mass of impurities and their fragments. According to the chemical structures and fragmentation patterns obtained by high resolution measures with accuracy ranging from 0.3 to −7.6 ppm, these impurities have been classified into three groups. The above fragmentation pathways and seven new impurities were reported for the first time.