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 poly mer samples using matrix-assisted laser desorption/ ionization Fourier transform mass spectrometry. Sustained off-resonance irradiation coll ision-induced dissociation (SORI-CID) can impart the energy required t o 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 polyisopre ne and polystyrene. For low-mass polymers, single oligomers are select ed for SORI dissociation and the remainder of the polymer distribution is left intact, allowing the other oligomer ions to be used for inter nal calibration. Ions resulting from SORT-CID consist of lower mass in tact oligomer species and, equally important, distributions of the oli gomer fragments which have lost an end group through chain cleavage. T his latter feature facilitates identification of the end groups. The u pper mass limit of this technique is determined by cyclotron frequency spacing as one moves to higher masses. Decreased frequency spacing tr anslates to SORI 'spill-over' to neighboring oligomers causing retenti on of some while ejecting others, rendering data interpretation more a mbiguous. (C) 1998 Elsevier Science B.V. All rights reserved.