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

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 <4 ms, which allows fast tuning of the mass bandpass in concert with and at the speed of the analyzing quadrupole. When the cell is operated with ammonia, the field reduces ion-ammonia cluster formation, further enhancing the transmission of atomic ions that have a high cluster formation rate. Ni center dot(NH3)(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 O-2 for suppression of Xe-129(+), the formation of (IH2+)-I-127 by reactions with gas impurities limits the detection of I-129 to isotopic abundance of similar to10(-6). In-cell energy discrimination against (IH2+)-I-127 utilizing a retarding axial field is shown to reduce the abundance of the background at m/z = 129 to ca. 3 x 10(-8) of the I-127, signal. In-cell energy discrimination against (IH2+)-I-127 is shown to cause less I+ loss than a post-cell potential energy barrier for the same degree of (IH2+)-I-127 suppression.