Inductively coupled plasma mass spectrometer with axial field in a quadrupole reaction cell

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Abstract
A novel reaction cell for ICP-MS with an electric field provided inside the quadrupole along its axis is described. The field is implemented via a DC bias applied to additional auxiliary electrodes inserted between the rods of the quadrupole. The field reduces the settling time of the pressurized quadrupole when its mass bandpass is dynamically tuned. It also improves the transmission of analyte ions. It is shown that for the pressurized cell with the field activated, the recovery time for a change in quadrupole operating parameters is reduced to n + cluster formation in a cell operated with a wide bandpass (i.e., Ni+ precursors are stable in the cell) is shown to be dependent on the axial field strength. Clusters at n = 2–4 can be suppressed by 9, 1200, and >610 times, respectively. The use of a retarding axial field for in-situ energy discrimination against cluster and polyatomic ions is shown. When the cell is pressurized with O2 for suppression of 129Xe+, the formation of 127IH 2 + by reactions with gas impurities limits the detection of 129I to isotopic abundance of ∼10−6. In-cell energy discrimination against 127IH 2 + utilizing a retarding axial field is shown to reduce the abundance of the background at m/z = 129 to ca. 3 × 10+ of the 127I+ signal. In-cell energy discrimination against 127IH 2 + is shown to cause less I+ loss than a post-cell potential energy barrier for the same degree of 127IH 2 + suppression.

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