Patent ID: 7045797
Filing Date: 2006-05-16
Classification: H01J

Abstract:
1. A method of operating a mass spectrometer having an elongated rod set, said rod set having an entrance end and an exit end and a longitudinal axis, said method comprising: (a) admitting ions into said entrance end of said rod set, (b) trapping at least some of said ions in said rod set by producing a barrier field at an exit member adjacent to the exit end of said rod set and by producing an RF field between the rods of said rod set adjacent at least the exit end of said rod set, (c) said RF and barrier fields interacting in an extraction region adjacent to said exit end of said rod set to produce a fringing field, and (d) energizing ions in said extraction region to mass selectively eject at least some ions of a selected mass to charge ratio axially from said rod set past said barrier field, wherein said RF field is a two-dimensional substantially quadrupole field having a quadrupole harmonic with amplitude A 2 , an octopole harmonic with amplitude A 4 , and a hexadecapole harmonic with amplitude A 8 , wherein A 8 is less than A 4 , and A 4 is greater than 0.1% of A 2 .