Patent ID: 7855361

Claim:
An ion detector for selectively detecting positive and negative ions, the ion detector comprising: an ion guide including a plurality of electrodes arranged about a first axis and configured to apply an RF field to constrain ions to motions generally about the first axis; a positive ion detection device including a positive ion inlet disposed at a first side of an ion output section, the positive ion inlet being offset from and at an angle to the first axis, the positive ion detection device configured to apply a negative voltage bias and accelerate positive ions along a positive ion path directed from the ion guide into the positive ion inlet, the positive ion path including a component directed along a second axis orthogonal to the first axis; and a negative ion detection device including a negative ion inlet disposed at a second side of the ion output section opposite the first side, the negative ion inlet being offset from and at an angle to the first axis, the negative ion detection device configured to apply a positive voltage bias and accelerate negative ions along a negative ion path directed from the ion guide into the negative ion inlet, the negative ion path including a component directed along the second axis generally opposite to the component of the positive ion path.