IsoPrime User’s Guide
Version 1.01 IsoPrime100 User’s Guide Page 85 of 219
It is now advisable to recheck the instrument peak shape and, if acceptable, check instrument
stability and linearity.
INSTRUMENT LINEARITY
Instrument linearity is most affected by the relationship of the Extraction % (EX) and the Ion
Repeller (IR). If instrument linearity cannot be achieved it can be useful to change one of these
parameters to a new “fixed” setting and retune the instrument source around this.
For example:
IR “fixed” at -7 V
EX set at 75%
Run Linearity.
Linearity is outside specification.
Retune, reduce EX to 74%.
Optimise HP, EV, ZV
Run Linearity.
Linearity is better but still out of specification.
Retune, reduce EX to 72%.
Optimise HP, EV, ZV
Run Linearity
Linearity is now acceptable.
If, having reduced the EX to outside suggested levels, linearity cannot be achieved. The above
can be repeated after changing the IR to a different “fixed” setting and ensuring all other
parameters are maximised.
If tuning for maximum sensitivity it is advisable to start tuning from tuning parameters already
proven to be linear; change one source parameter at a time and recheck linearity. With this
approach it is easy to identify which source parameter is causing the instrument to be non
linear.
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