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Agilent 7500 ICP-MS ChemStation Operator's Manual
Tuning
ShieldTorch System
The ShieldTorch system is very powerful with features such as a Cool plasma for
Fe, K, Ca analysis at the ppt level, a High sensitivity mode and a Soft extraction
mode.
The ShieldTorch is not applicable to all sample types and it must be carefully
considered whether it is appropriate for the particular samples and elements that are
to be analyzed.
Theory of the ShieldTorch System
The polyatomic ion, such as ArO, is formed behind the interface and plasma.
At behind the interface
The potential in the plasma is grounded through the interface and the secondary
discharge occurs at this time. The secondary discharge ionizes molecules such as
ArO, ArH, and ArAr, and atoms behind the sampling cone. When the ShieldTorch
system is used, the shield plate inserted between the torch and the RF coil eliminates
the capacitive coupling between the plasma and the RF coil, so that the potential in
the plasma is lower than that without the ShieldTorch system. As a result, there is
no longer a secondary discharge and polyatomic ions such as ArO, ArH and ArAr,
are not ionized behind the sampling cone.
4-18
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- Tuning for Sensitivity (Agilent 7500A)
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