Characterization of Polypeptide Antibiotics of the Polymyxin Series by Liquid Chromatography Electrospray Ionization Ion Trap Tandem Mass Spectrometry

A selective reversed phase liquid chromatography/mass spectrometry (LC/MSn) method is described for the identification of related compounds in commercial polymyxin B samples. Mass spectral data for these polypeptide antibiotics were acquired on a LCQ ion trap mass spectrometer equipped with an electrospray ionization probe operated in the positive ion mode. The LCQ ion trap is ideally suited for the identification of the related substances because it provides on‐line LC/MSn capability. The main advantage of this hyphenated LC/MSn technique is the characterization of novel related substances without time‐consuming isolation and purification procedures. Using this method six novel related substances were partially identified in a polymyxin B bulk sample. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd.