Multiple stage mass spectrometer

Abstract

A highly sensitive multiple stage (MS ) mass spectrometer is disclosed, capable of eliminating losses of ions during the isolation stage. Ions of interest are isolated (by m/z value) without rejecting ions of other m/z values, permitting the selected ions to be dissociated, while the rest of the ion population is available for subsequent isolation, dissociation and analysis of fragment ions. One preferred instrument includes a pulsed ion source coupled with a linear array of mass selective ion trap devices, at least one trap being coupled to an external ion detector. Each ion trap is configured with a storing cell for ion trapping interspersed between a pair of guarding cells, all aligned along their z axis. Radio frequency (RF) and direct current (DC) voltages are applied to electrodes of the ion trap device to retain ions within the storing cells. Each trapping cell has a sub-region in which the dynamical motion of the ion exhibits m/z-dependent resonance frequencies along the z direction, allowing the ion motion to be selectively excited by m/z value. The AC voltages can be combined with time-resolved changes in the applied DC voltages to enable individual trapping cell to be switched between ion trapping, mass selecting and ion fragmenting modes. Ions may be selectively transferred between ions traps, and selectively dissociated within each trap to enable a higher sensitivity MS operation. Various ion trapping devices are disclosed, namely, harmonic linear traps, Paul traps, and quadrupole traps.