Page 309 - Inorganic Mass Spectrometry - Fundamentals and Applications

296 s all id ay et al.

2
Fi~~~e Schematic for the Nu Instruments Nu Plasma.

that used in conventional ICP-MS, and the front end is fitted with a water-cooled
nickel sampler (1 .O-m-diameter aperture) and skimer (0*6-m-diameter aper-
ture) cones. The extracted 4-kV ions are accelerated imediately behind the skim-
mer and focused down onto and through an intermediate circular aperture (Fig.
8.3). This circular image is then matched to the rectangular defining slit of the mass
spectro~eter, using two independent (2-kV) Einzel lenses so as to ensure minimal
cross talk between the horizontal (y) and vertical (z) lens actions. Electrostatic
beam steering is provided at all necessary points to ensure the ion beam stays on
axis (Fig. 8.3). The ins~ment uses a 35-cm-radius ESA, followed by a 25-cm-ra-
dius magnet; the ion optics are designed to allow full transmission of the plasma
ions of interest with minimal degradation of peak shape quality. No deceleration
and reacceleration of the ions to accomplish energy focusing are used on this in-
s~ment. Hence, the standard C con~guration is possible and the focused ion beam
maintains 4-kV energy throughout the analyzer. Vertical (2) focusing of the ion
the
is
beam through the mass spectrometer achieved by the use of both Einzel lenses
placed in front of the ESA and the non-normal exit pole on the magnet.
Because the spatial separation between ion beams of adjacent isotopes is
mass dependent, in nearly all magnetic sector inst~ments it is necessary to alter
the distance between collectors mechanically. This is a particular problem for ICP