Low resolution tuning 2-11
5. Optimize the values of the lens controls on the Lenses 1 and Lenses 2
tabs to obtain the best peak shape (with minimum tailing) and intensity.
Tip: The controls in the Lenses 1 page tune the instrument for optimum
intensity. The controls in the Lenses 2 tab tune the instrument for
optimum resolution, that is, peak shape.
With some of the lenses controlled via the Lenses 1 tab, a small sacrifice
in intensity can reduce or remove a peak tail and give better resolution
and improve transmission. An increased intensity does not necessarily
give greater sensitivity, because sensitivity is lost on an incorrectly
focused beam.
Note: When this tuning is complete, the peak has a flat top, because the
collector slit is still set to be wider than the ion beam, which scans across
the slit.
See “Collector slit” on page G-8.
Tuning controls :
Location in
Tune
window
Control Notes
Source tab Ion Repeller (V) Ion Repeller (V) and Focus 1 are
interactive and must be tuned in
conjunction with each other.
Focus 1
Beam Centre Beam Centre, Focus 2, and
Y Deflect 1 are interactive and must
be tuned in conjunction with each
other.
Focus 2
Lenses 1 tab Y Deflect 1
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