Characterisation of macromolecules using electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry
Multipole storage-assisted dissociation (MSAD), in which ions are stored for extended periods of time in a multipole ion-trap, represents one of the most recent and simplest methods by which structurally informative fragments can be obtained. A potential array investigation of MSAD is reported. It was found that the average kinetic energy of the ion was similar to the energy of a single IR photon and the average kinetic energy of an ion during sustained off-resonance irradiation collision-induced dissociation (SORICID), thus explaining the similar fragments that have been obtained using these techniques. The ion's average kinetic energy and its collision frequency was investigated as a function of the ion's charge, mass and mean free path, the space charge present in the hexapole ion trap and the applied radio frequency (RF) potential. All but one of the dependencies, namely the RF potential dependence, were in agreement with experimental results. The disagreement between the experimental results and the simulation results was due to the rate of charge accumulation depending on the applied RF potential. Without prior isolation, MSAD is limited in that it does not permit the isolation of a parent ion and the detection of all fragment ions. Collision-induced dissociation (CID) inside a Fourier transform ion cyclotron resonance (FTICR) cell permits the isolation, fragmentation and detection of all daughter ions. Furthermore the inherent advantages ofFTICR mass spectrometry, higher resolution and mass accuracy, are also afforded to the fragment ions as well as the initial parent ions. Using this technique, all of the components of a commercially available polymeric dye were assigned and the more intense components structurally characterised. This structural characterization highlighted new information regarding the low-energy multiple collision CID of substituted polyesters. Included in these findings was the charge-induced nature of the 1,4-H rearrangement, the participation of amino groups in the fragmentation mechanisms the collisional ring opening of a cyclic polymer. The two previous techniques involve collisions with neutral atoms to increase the internal energy (vibrational) of the ion to obtain the structurally informative fragments. In a similar manner, the fragments obtained after electronic excitation provide a powerful tool with which the electronic structure of molecules can be studied. An ion imaging study of HCI (2+ 1) resonance-enhanced multiphoton ionisation (REMPI) revealed new predissociation channels, an electronic-vibrational-rotational state dependence of the angular distribution of the fragments and vibrational state dependent HCI+ photodissociation. The additional predissociation channels continued the pseudoRydberg continuum of the superexcited states responsible for the previously detected predissociation channels. The complicated angular distribution behavior of the fragments is thought to reflect the diabatic state character of the resonant state, which then determines which superexcited states are accessible.