Obtaining the Dielectric Constant of Polymers from Doubly Charged Species in Ion-Mobility Mass Spectrometry

Abstract

Ion-mobility mass spectrometry of doubly charged polyethylene glycol (PEG) is performed after electrospray-ionization time-of-flight mass spectrometry and the dependency of the effective collision cross-section, CCSeff, on the number of monomer units, n, is evaluated with the help of molecular dynamics simulations. Assuming a balance between elastic and Coulomb forces inside short and asymmetric doubly charged chains, a method is developed for evaluating the dielectric constant, e, which is found to be 7.87 for PEG for n = 14–28. From the same experiment at higher chain lengths, the characteristic ratio Cn of 4.30 for PEG (n ≥ 63) can be evaluated according to an earlier reported method, which is demonstrated here to also work with doubly charged species. The proposed method enables an extremely swift and precise measurement both of e and Cn of polymer that is free of solvent or impurities from one single experiment.