Sustained off-resonance irradiation and collision-induced dissociation for structural analysis of polymers by MALDI-FTMS

A method is presented for collision-induced structure analysis of polymer samples using matrix-assisted laser desorption/ ionization Fourier transform mass spectrometry. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) can impart the energy required to initiate fragmentation of intractable low mass polymers with masses below 3000 Da. The method has been applied to both polar poly(ethylene glycol) polymers and nonpolar hydrocarbon polymers such as polyisoprene and polystyrene. For low-mass polymers, single oligomers are selected for SORI dissociation and the remainder of the polymer distribution is left intact, allowing the other oligomer ions to be used for internal calibration. Ions resulting from SORT-CID consist of lower mass intact oligomer species and, equally important, distributions of the oligomer fragments which have lost an end group through chain cleavage. This latter feature facilitates identification of the end groups. The upper mass limit of this technique is determined by cyclotron frequency spacing as one moves to higher masses. Decreased frequency spacing translates to SORI 'spill-over' to neighboring oligomers causing retention of some while ejecting others, rendering data interpretation more ambiguous. (C) 1998 Elsevier Science B.V. All rights reserved.