Structural analysis of polymer end groups by electrospray ionization high-energy collision-induced dissociation tandem mass spectrometry

Chemical structures of polymer end groups play an important role in determining the functional properties of a polymeric system. We present a mass spectrometric method for determining end group structures. Polymeric ions are produced by electrospray ionization (ESI), and they are subject to source fragmentation in the ESI interface region to produce low-mass fragment ions. A series of source-fragment ions containing various numbers of monomer units are selected for high-energy collision-induced dissociation (CID) in a sector/time-of-flight tandem mass spectrometer. It is shown that high-energy CID spectra of source-induced fragment ions are very informative for end group structure characterization. By comparing the CID spectra of fragment ions with those of known chemicals, it is possible to unambiguously identify the end group structures. The utility of this technique is illustrated for the analysis of two poly(ethylene glycol)-based slow-releasing drugs where detailed structural characterization is of significance for drug formulation, quality control, and regulatory approval. Practical issues related to the application of this method are discussed.