Ultrahigh Mass Accuracy in Isotope-Selective Collision-Induced Dissociation Using Correlated Sweep Excitation and Sustained Off-Resonance Irradiation: A Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Case Study on the [M + 2H](2+) Ion of Bradykinin.

Using electrospray ionization with a 9.4 T Fourier transform mass spectrometer, fragment ion spectra were acquired for a single isotopomer of doubly protonated bradykinin (molecular mass, 1059.6 Da). Correlated sweep excitation methods were applied to mass-select the single isotopomer (m/z = 530.8). Sustained off-resonance irradiation was used to activate and fragment the ions. The accuracy (in terms of m/z) in detection of the fragment ions was on average 1.2 ppm, making the assignments unambiguous. The methods employed would be generally applicable to ions in the mass range of approximately 50 Da to 50 kDa.