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 ET-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 greater than or equal to 20 000 at m/z less than or equal to 1000), and mass accuracy (less than or equal to 50 ppm for peptide fragments of m/z less than or equal to 1000) are demonstrated for CID product ions of the cyclic peptide, gramicidin S.