Patent ID: 7759637

Claim:
A method of analyzing ions with a mass spectrometer, the method comprising: (a) providing a first ion guide having a first end and a second end; (b) introducing a first group of ions and a second group of ions into the first ion guide, the second group of ions being opposite in polarity to the first group of ions; (c) applying an RF voltage potential to the first ion guide for confining the first group of ions and the second group of ions radially within the first ion guide; (d) providing a trapping barrier to the second end of the first ion guide for trapping the first group of ions within the first ion guide, wherein the trapping barrier is a DC voltage barrier of the same polarity as the first group of ions; and (e) providing an axial field for pushing the first group of ions toward the trapping barrier and for pushing the second group of ions toward the first end.