Hardware manual

1-18 Agilent 7500 Series ICP-MS Hardware Manual
1Overview
Quadrupole
The quadrupole mass analyzer consists of four long metal rods with a
hyperbolic cross section which are arranged parallel to each other, and have
RF and DC voltages applied to them. By varying these voltages, the rods act as
a mass filter allowing only ions of a specific mass- to- charge ratio to pass
through the center of the quadrupole at any given combination of applied
voltages. All other masses are unstable and collide with the rods. These
voltages are ramped very rapidly so the quadrupole can scan the entire mass
range (2- 260 amu) in 100 milliseconds. As a result, spectra of mass versus
intensity can be obtained for all elements virtually simultaneously.
Quadrupoles are limited effectively to unit mass resolution so they can't
resolve polyatomic and isobaric interferences. However, of all of the elements
detectable by ICP- MS, only indium does not have an isotope that is free from
overlap by another element.
Detector
After passing through the quadrupole, ion signals are measured by the
electron multiplier detector. Both the quadrupole and detector are located in
the analyzer stage, which is evacuated by a second turbo- molecular pump.
The electron multiplier (EM) has many dynodes. When an ion enters the EM,
the ion hits the first dynode and a shower of electrons is generated. The
electrons then hit the next dynode generating more electrons.
Figure 12 Electron Multiplier
+ HV
Amp
Amp
- HV
Electron
Ion
M
+
e
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e
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