Selective removal of matrix ion peaks in plasma source time-of-flight massspectrometry: ion deflection and detector gating

A significant problem in plasma source time-of-flight mass spectrometry (TO FMS) is the saturation of detectors due to plasma gas and matrix ions. This paper outlines two experimental procedures to minimize the detector respon se to large ion currents in a glow discharge time-of-flight mass spectromet er. One novel solution is a deflection device that includes two parallel pl ates for ion ejection and two sleeve plates (after the deflection plates) t o reduce ion and neutral scattering. Another approach is to gate the detect or, by lowering the voltage on the microchannel plates, when an intense ion pack is expected. Both approaches are efficient in eliminating the plasma gas peaks and matrix ions in plasma source time-of-flight mass spectrometry . The matrix ion intensity can be reduced by several orders of magnitude, w ith minimal influence on the analyte ions. The detector gating technique re quires a high peak current pulse with a flexible rise time. However, this a pproach will cause an electrical ringing to be superimposed on the analytic al signal. Therefore, ion deflection is the method of choice for plasma TOF MS.