Collisionally activated decomposition of poly(ethylene glycol)s: An investigation of high‐mass ion abundances in the collisional activation technique with large molecules

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Abstract
The utility of the collisional activation technique in structure determination of ions is limited as parent ion mass increases. Optimum collisionally activated dissociation yield is often obtained at parent masses of 1000–2000 u, after which daughter ion yield decreases. The apparent decrease in the efficiency of the collisional activation process has been thought of as a degree‐of‐freedom effect: as new rotational‐vibrational modes are added to the parent ion, its lifetime with respect to dissociation increases. We have investigated this effect using an easily characterized system of several poly(ethylene glycol) homologs from the 15‐mer to the 35‐mer. Observed trends in the collisional activation spectra as parent mass increases support the postulated ‘degree‐of‐freedom’ effect in general. The loss of C2H4O from the [M − H]− parents, a fragmentation which has a high activation barrier, however, actually becomes more favored as the parent ion becomes larger. This effect is explained in terms of statistical rate theory.