A mass spectrometer ion reaction device, useful for performing ion-ion reactions (eg. ETD, PTR) is described. The device includes a plurality of non-linear rods, that form a pair of quadrupole rod sets. The device includes an axial passageway, that allows injections of ions of both polarities into the device, and a three dimensional trapping region. Anions and cations that are injected into the device are spatially separated into different trapping regions by a DC dipole electric field generated by a DC voltage source. The device also includes a plurality of lenses to confine, transmit or receive ions in/from the device.