Mass-selective ion accumulation and fragmentation in a linear octopole iontrap external to a Fourier transform ion cyclotron resonance mass spectrometer

Electrosprayed protein ions are accumulated and mass selected in an externa l linear octopole trap before injection into a Fourier transform ion cyclot ron resonance (FTICR) mass spectrometer. Mass selection is performed by app lication of superimposed rf and de octopole electric potentials during ion accumulation. Ion trajectory stability and mass selection in the octopole f ield are explained qualitatively by analogy to a quadrupole mass filter. Ac cumulation of ions from a selected m/z range is demonstrated experimentally for 7 and 9.4 T electrospray ionization (ESI) FTICR mass spectrometers. Io n fragmentation in the octopole may occur under certain operating condition s. (C) 2000 Elsevier Science B.V.