Tandem mass spectrometry of large biomolecule ions by blackbody infrared radiative dissociation

A new method for the dissociation of large ions formed by electrospray ionization is demonstrated, Ions trapped in a Fourier transform mass spectrometer at pressures below 10(-8) Torr are dissociated by elevating the vacuum chamber to temperatures up to 215 degrees C. Rate constants for dissociation are measured and found to be independent of pressure below 10(-7) Torr, This indicates that the ions are activated by absorption of blackbody radiation emitted from the chamber walls, Dissociation efficiencies as high as 100% are obtained, There is no apparent mass limit to this method; ions as large as ubiquitin (8.6 kDa) are readily dissociated, Thermally stable ions, such as melittin 3+ (2.8 kDa), did not dissociate at temperatures up to 200 degrees C. This method is highly selective for low-energy fragmentation, from which limited sequence information can be obtained, From the temperature dependence of the dissociation rate constants, Arrhenius activation energies in the low-pressure limit are obtained, The lowest energy dissociation processes for the singly and doubly protonated ions of bradykinin are loss of NH3 and formation of the b(2)/y(7) complementary pair, with activation energies of 1.3 and 0.8 eV, respectively, No loss of NH3 is observed for the doubly protonated ion; some loss of H2O occurs, These results show that charge-charge interactions not only lower the activation energy for dissociation but also can dramatically change the fragmentation, most likely through changes in the gas-phase conformation of the ion, Dissociation of ubiquitin ions produces fragmentation similar to that obtained by IRMPD and SORI-CAD, Higher charge state ions dissociate to produce y and b ions; the primary fragmentation process for low charge state ions is loss of H2O.