A method of analyzing ions is provided having a first ion guide with first and second ends and introducing a first group of ions and a second group of ions of opposite polarity into the first ion guide, and applying an RF voltage potential to the first ion guide for confining the first and second groups of ions radially within the first ion guide. A first trapping barrier is provided to the first end of the first ion guide for trapping the first group of ions within the first ion guide and a second trapping barrier is provided to the second end of the first ion guide for trapping the second group of ions within the first ion guide and an axial field is provided for pushing the first group of ions toward the first trapping barrier and pushing the second group of ions toward the second trapping barrier.