Synchrotron UV photoactivation of trapped sodiated ions produced from poly(ethylene glycol) by electrospray ionization

Rationale By taking advantage of the gas-phase decompositions of polymer ions, tandem mass spectrometry of polymers allows us to obtain more accurate structural information than from a simple mass measurement. Applied to a model polymer, the goal of this work was to evaluate the performances of an activation technique based on ultraviolet (UV) irradiation, as an alternative to conventional collisional activation. Methods Sodiated poly(ethylene glycol) produced by electrospray ionization was isolated in a linear ion trap, then submitted to synchrotron UV irradiation over a range of wavelengths (52 to 248 nm). Fragmentation pathways resulting from UV photoactivation were investigated. The proposed mechanisms take into account: (i) the comparison with collision-induced dissociation (CID) product ions, (ii) the effect of wavelength-tunable UV activation, and (iii) deuterium-labeling and various other complementary experiments. For the highest molecular weight compounds, ion mobility spectrometry was used before UV photoactivation. Results Synchrotron UV irradiation can induce dissociation of poly(ethylene glycol) sodiated ions without the requirement of the presence of a specific chromophore, if the photon energy is above 10 eV. UV photoactivation of poly(ethylene glycol) ions can yield fragmentations that differ from those in classical low-energy CID, especially from higher masses (>4000 g mol-1 ). A successful coupling of UV photoactivation with ion mobility pre-filtering was presented. Conclusions UV activation combined or not with pre-filtering ion mobility is a promising alternative approach for the structural characterization of polymers. UV synchrotron radiation with a tunable wavelength was a great opportunity to study the effect of the photon energy, and to probe the mechanisms of ion decomposition from poly(ethylene glycol).