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Abstract

Methods and apparatus for improving the performance of triple quadrupole tandem mass spectrometers consisting of constructing the collision cell surrounding the second quadrupole structure, into which collision gas is admitted, with end plates composed of leaky dielectric material which appear to radio-frequency electric fields as a dielectric and to dc electric fields as a conductor. The result is that the rf fringe fields extend farther away from the ends of the poles of the first and third analyzing quadrupole mass filter than do the dc fringe fields, thus keeping the ions on stable trajectories in the regions between the analyzing quadrupoles and the end plates of the collision cell, and improving the transmission of ions. The effect is enhanced by applying the same frequency and phase of the ac voltages applied to all three quadrupole structures.

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