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quadrupole mass spectrometer analyzer. After dispersion the ions are detected in the normal way with
an electron multiplier tube. A diagram of the ICP interface and the quadrupole mass spectrometer is
shown in Figure 9.3.

Figure 9.3
The Liquid Chromatography/Inductively Coupled Plasma
Mass Spectrometer (LC/ICPMS) Tandem Instrument

The quadrupole mass spectrometer separates the ions on a basis of mass-to-charge ratios (m/z).
Unfortunately, the ICP is not a very efficient excitation/ionization source for nonmetals such as the
halogens and for elements such as arsenic and selenium. Helium plasma has an ionization potential of
24.5 eV compared with that of argon, 5.75 eV, and is consequently a more efficient
excitation/ionization source. It follows that the microwave induced helium plasma is likely to be more
efficient. The arrangement for the microwave induced helium plasma is very similar to that of the ICP
torch as depicted in Figure 9.3, except that the plasma is induced by a resonant microwave cavity
surrounding the body of the