Hardware manual

1-16 Agilent 7500 Series ICP-MS Hardware Manual
1Overview
Interface/Vacuum System
After the analyte ions are formed, they are extracted into the first vacuum
stage through a hole in the front plate of the vacuum chamber referred to as
the sampling cone. Ions pass through the sampling cone into the interface,
which is an expansion region evacuated by a rotary pump. The ions then pass
through a second orifice called the skimmer cone, which acts as a differential
aperture between the interface and intermediate vacuum stage. Ions are
extracted from the interface stage and collimated by two conical extraction
lenses prior to focusing by the ion optics. (Figure 11). The intermediate stage
contains the ion optic system and is evacuated by a turbomolecular pump.
Ion Lenses
To achieve high signal sensitivity, the ion beam must be focused before
entering the quadrupole mass analyzer. The ion lenses perform the dual role of
focusing the ion beam and preventing photons and neutral species (arising
from the plasma) from reaching the detector, giving the Agilent 7500a very low
random background.
Figure 11 Ion Lenses (7500a)
Although electron multipliers are very sensitive ion detectors, they are also
sensitive to photons. To eliminate photon noise, the quadrupole and detector
are mounted off- axis to the ion beam entering the system from the interface.