Page 307 - Inorganic Mass Spectrometry - Fundamentals and Applications

al.
294 ~ull~~uy
et
high mass
Faraday

Outline of the multiple-collector inductively coupled plasma mass spectrome-
ter (VG Elemental Plasma 54) at the University of Michigan (U-M). The U-M inst~ment
is equipped with an extra 30-cm energy filter for high-abundance sensitivity measurements.
(From Halliday et al., 1998b.)

2,
sua1 Basic, rather than the more intractable Modula and the latest instrumenta-
tion operates from Windows 95, NT, or Unix platforms.
We first describe the P54 and then outline the ways in which the most recent
inst~ments differ from it. Schematics for the inst~ments are shown in Figs. 8.1
to 8.6.

The P54 is a double-focusing forward geometry inst~ment equipped with an array
of
of mechanically adjustable Faraday collectors (Fig. 8.1). Most the instrument is
at ground, but the source and its associated pumping are floated high potential.
at
The ions are extracted at high voltage and two quadrupole dc lenses are used to
focus the ion beam profile onto the analyzer entrance slit (Fig. 8.1). A small elec-
trostatic analyzer (ESA) is then used to provide energy focusing and match the en-
of
ergy dispersion of the plasma source with that the magnetic sector analyzer, such
that the ions are energy-focused in the directional focal plane at the collectors. To
permit effective energy focusing by a small radius (10-cm) ESA with a small volt-
a
age offset, the entrance utilizes deceleration lens. The ions are then reaccelerated