Patent ID: 8227751

Claim:
An ion guide or ion trap comprising: a plurality of electrodes; an AC or RF voltage supply arranged and configured to apply an AC or RF voltage to at least some of said plurality of electrodes in order to confine at least some ions radially within said ion guide or ion trap; first means arranged and adapted to maintain one or more DC, real or static potential wells along at least a portion of the axial length of said ion guide or ion trap in a first mode of operation; and second means arranged and adapted to apply a supplemental AC voltage or potential to said electrodes in order to excite parametrically at least some ions, in use, within said one or more potential wells, wherein said supplemental AC voltage or potential has a frequency σ which excludes the fundamental frequency ω of the at least some ions which are excited parametrically; wherein said ion trap or ion guide comprises a linear ion trap or ion guide; and wherein said second means is arranged and adapted to cause certain ions to be parametrically excited and axially ejected from said ion guide or ion trap.