Development of a mass spectrometry method for the characterization of a series of chitosan

Chitosan has multiple biological activities, but a sensitive and rapid characterization method is yet to be developed for its further application. This study presented an optional mass spectrometry method for the characterization of chitosan. Nine kinds of chitosan (degree of deacetylation (DD), 63.08%-89.06% & MW, 106.1-485.0 kDa) were adopted for the method development. Most species of chitosan, detected by an ESI-MS technique, were observed below 1000 m/z, which seemed that only chito-oligosaccharide (COS) impurities were detected. Then, a sensitive UPLC-ESI-MS/MS method was established to assess the COS impurities in chitosan, and no COS impurities were detected. However, dissociation of chitosan and COSs in the ESI source were observed, and then the mass spectra patterns were deeply evaluated via an accurate Q-TOF mass spectrometer. Our research demonstrated that the mass spectra of COSs and chitosan resulted from the dissociation of glycosidic linkage and dehydration. Although the distribution of GlcN and GlcNAc units in these chitosan samples might be different, similar dissociation efficiencies were observed. Furthermore, good linearities were obtained between the intensities of product ions, detected by an UPLC-pseuedo-MS2 method, and DDs determined by conventional method. This method could be suitable for the DD determination and quantitative analysis of chitosan.