Applications of new mass spectrometric technologies for the structural characterisation of synthetic polymers

Abstract

The work detailed herein describes the developments made using new mass spectrometric techniques for the structural characterisation of synthetic polymers. Electron-based tandem mass spectrometry techniques Electron Induced Dissociation (EID) and Hot Electron Capture Dissociation (HECD) have proven to be highly effective methods of characterising synthetic polymers. The product ion spectra obtained provided comparable structural information to Collision Induced Dissociation, both in terms of the types of ion formed and the monomer sequence covered. The application of EID and HECD to copolymer analysis provided a facile method of differentiating copolymers with a variety of architectures, including identification of structural isomers.
Control of the charge carrier present demonstrated that electron-based tandem mass spectrometry results could be manipulated to maximise the amount of structural information obtained. For synthetic polymers, improved fragmentation efficiency using EID was achieved when the charge carrier present was a strong reducing agent. EID analysis of small organic molecules, demonstrated that the present of different charge carriers resulted in product ions that provided complementary structural information. This was proposed to be due to the different locations of charge carrier attachment within the molecule, which is supported by molecular modelling calculations.
The application of Atmospheric pressure Solids Analysis Probe (ASAP) mass spectrometry facilitated the analysis of common synthetic polymers directly from solids, circumventing issues regarding solubility. Key instrument parameters were identified that maximised the intensity of the molecular ion peaks whilst restricting in-source fragmentation. The synthetic polymers were ionised without the requirement for metal salts, forming protonated and radical cation molecular ions. CID tandem mass spectrometry of these precursor ions demonstrated that they fragmented readily, where analysis of radical cations resulted in product ions that are not observed during CID of even electron precursor ions. ASAP, for the first time, was successfully applied to the structural characterisation of an insoluble block copolymer. The product ions provided information about the individual components of the copolymer, which could not be obtained by any other analytical technique.