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 su bjected to off-resonance dipolar excitation to promote collision-induc ed dissociation(CID), while product ions are simultaneously axialized by broad-band azimuthal quadrupolar excitation in the presence of argo n collision gas. In this way, radial diffusional loss of product ions is greatly reduced; moreover, the axialized product ions may then be e fficiently transferred to the analyzer trap for high-resolution detect ion. Significant improvements in FT-ICR detection efficiency, mass res olving power (m/Delta m greater than or equal to 20 000 at m/z less th an 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 demonstra ted for CID product ions of the cyclic peptide, gramicidin S.