Patent ID: 7034293

Claim:
A method for controlling ion motion comprising: (a) generating an ion trapping field comprising a quadrupole component by applying a main AC potential to an electrode structure of linear ion trap, the electrode structure having a central axis and comprising a pair of opposing electrodes positioned along an axis orthogonal to the central axis of the electrode structure; (b) applying an additional AC potential to the electrode pair to displace a central axis of the trapping field from a central axis of the electrode structure along the axis of the electrode pair; (c) introducing a nonlinear resonance condition in the trapping field; and (d) applying a DC offset potential to the electrode pair to set the a-q operating point for the electrode structure to a point in a-q space where the nonlinear resonance condition can excite ion motion only along the axis of the electrode pair and substantially in a single direction along the axis of the electrode pair.