Highly sensitive liquid chromatographic method combined with online ion suppression to remove interfering anions and mass spectrometry for impurity profiling of paromomycin sulfate

A previously developed high‐performance liquid chromatography method combined with pulsed amperometric detection allowed to separate many impurities of paromomycin. However, due to the presence of ion pairing agents and sodium hydroxide in the mobile phase, direct coupling to mass spectrometry for the identification of the chemical structures of the impurities was not an option. Indeed, ion suppression was encountered by trifluoroacetic acid and pentafluoroproponic acid in the mobile phase. A cation self‐regenerating suppressor, which was originally designed for increasing analyte conductivity of ammonia and amines analysis in ion chromatography, was coupled between the liquid chromatography and ion trap‐time of flight‐mass spectrometry and almost all trifluoroacetic acid and pentafluoroproponic acid in the mobile phase was removed. The limit of detection of paromomycin in this integrated system improved significantly to 20 ng/ml (0.4 ng). The chemical structures of 19 impurities were elucidated and seven impurities were reported for the first time.