MS/MS with High Detection Efficiency and Mass Resolving Power for Product Ions in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

We present a new FT-ICR method for MS/MS of trapped ions. Parent ions isolated in the source trap of a dual-trap FT-ICR/MS instrument are subjected to off-resonance dipolar excitation to promote collision-induced dissociation (CID), while product ions are simultaneously axialized by broad-band azimuthal quadrupolar excitation in the presence of argon collision gas. In this way, radial diffusional loss of product ions is greatly reduced; moreover, the axialized product ions may then be efficiently transferred to the analyzer trap for high-resolution detection. Significant improvements in FT-ICR detection efficiency, mass resolving power (m/delta m > or = 20,000 at m/z < or = 1000), and mass accuracy (< or = 50 ppm for peptide fragments of m/z < or = 1000) are demonstrated for CID product ions of the cyclic peptide, gramicidin S.