Each Of The Features For The Three Plasma Conditions - Agilent Technologies 7500 ICP-MS Operator's Manual

Agilent 7500 ICP-MS ChemStation Operator's Manual
Tuning

Each of the features for the three plasma conditions

There are 3 combinations to be considered: the standard system with normal plasma
conditions, the ShieldTorch system with normal plasma conditions, and the
ShieldTorch system with cool plasma conditions. Some features of each follow:
Standard system (normal plasma)
Advantage
• Relatively resistant to matrix effects.
Disadvantage
• Difficult to analyze those elements which suffer interferences by polyatomic ions
containing Ar and C, e.g. K, Ca, and Fe.
The ShieldTorch system (High Sensitivity mode)
With the ShieldTorch system, the pattern for extracting ions from plasma at the
interface varies. The Plasma gets into the backside of the Skimmer and the
interaction between the electric field from the extraction lens and the plasma decides
the extraction condition. At this time, the condition for the space charge effect and
ion focus will be quite different from those with no shield plate.
Under this condition, two ion lens modes are available to select. The Extraction
mode realizes the ion extraction under far advantageous conditions and higher
sensitivity. The Soft extraction mode reduces the background.
Advantages
• It gives a higher sensitivity than when it is under the Standard torch and Normal
plasma condition. The sensitivity can be especially high in the Extraction mode.
• In the Soft extraction mode, background caused by the interface will be reduced.
Especially, it is effective in decreasing the alkaline background with elements,
such as Li and Na, which are increased by the memory at the interface. Thus, the
detection limit of the element will be expanded.
• In the Soft extraction mode, low mass sensitivity is lowered in use and this will
reduce the random background. Then, the BEC(Background Equivalent
Concentration) will be substantially improved in mid mass or high mass.
Disadvantage
• Matrix effects are more severe when the shield plate is fitted.
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