Function and setup of the PlasmaQuant MS
PlasmaQuant MS product family
28
The electric fields produced by ion optics can alter the path of ions in much the same
way as optical components like lenses, prisms or a parabolic reflectors can alter the
path of photons in a beam of light.
The patented ion optics system captures ions emerging from the back of the skimmer
cone and focuses them into the mass analyzer, set 90° off the axis. The central
component of the ion optics is the ReflexION. This ion mirror is a flat ring consisting of
four electrodes that uses a parabolic electrostatic field to reflect and focus the ion
beam into the aperture of the mass analyzer. The ion mirror concept allows for
controlling the ion beam along x, y and z-axis (3D), disregarding the energy spread of
the ions. As a result, a sharply focused, round shaped ion beam (
∅
1 mm) enters the
mass analyzer guaranteeing the highest possible sensitivity. Furthermore, the open
structure lets photons, neutrals, droplets and particles pass straight through. As shown
in Fig. 12 ions are reflected by the electrostatic field while neutrals, photons, droplets
and solids continue straight through and are pumped away.
Fig. 12 ReflexION
1 Ion source
2 Interface cones
3 Ion beam
4 ReflexION Ion mirror
5 Entrance lens of the mass analyzer
6 Beam of neutral gas and photons
3.2.3
Mass analyzer
The high-definition mass analyzer system consists of the quadrupole mass filter and
patented curved pre-filters (see Fig. 13 p. 29). Pre-filters are placed in the first part of
the mass analyzer. They are composed of a set of four curved rods that are supplied
with RF power and act as a ion guide. These pre-filters cause the ions to follow a
curved trajectory. This effectively shields the mass filter from high-energy neutrals,
which are unaffected by the RF fields and continue on their original linear trajectories.
Thus, by setting the mass analyzer off the axis, continuous background is kept low and
the mass analyzer is shielded from contamination. This self-cleaning system
guarantees stable and maintenance free operation. Ions are separated according to
their mass-to-charge ratio (m/z) by the quadrupole mass filter. This consists of a set of
four conductive rods, mounted in insulating supports so that the rods are parallel and
the axes of the four rods lie on the corners of a square.
Ion Optics