Patent ID: 8785847

Claim:
An ion guide comprising: (a) a plurality of electrodes arranged about a device centerline to form an internal volume, at least two of the electrodes including a longitudinally extending gap, in which the longitudinally extending gap splits the electrode into two portions displaced from one another, the electrodes including an inward surface facing the device centerline to form a periphery of the internal volume; (b) a plurality of resistive inserts, each configured to be proximate to a gap, and radially aligned with respect to the device centerline, the resistive inserts including an innermost surface that faces the device centerline where the innermost surface is a first distance from the periphery of the internal volume; (c) a RF voltage supply configured to apply a RF voltage to the plurality of electrodes that establishes a RF field to radially confine ions, wherein the RF voltage supply is also configured to apply the RF voltage to the plurality of resistive inserts; and (d) a DC voltage supply configured to apply a first DC voltage to a first location of the resistive insert and a second DC voltage to a second location of the resistive insert that establishes an axial electric field gradient along at least a portion of the device centerline, in which the second DC voltage is different than the first DC voltage and the second location is longitudinally spaced apart from the first location.