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Figure 2.5
2.2 Quick Check of Air / Water
It is important to monitor the progress of the manifold pump down before initiating
a bakeout. Once the Pump Spin Speed reaches 100%, check for the presence of
a massive water peak (18 and 19 m/z, unlikely to be resolved) and the absence
of a nitrogen peak (28 m/z).
Only turn the trap on for a short period of time
(<5 seconds) so the filaments and multiplier are not adversely affected.
NOTE: This check of air water may not give usable results until after auto tuning
the system.
Go to Manual Control and click the
Active Segment
tab. Enter a Mass Range of
15 to 45 m/z (refer to Figure 2.6, Full Scan Parameters tab). Also enter a Fixed
Ionization Time of 100 microseconds for internal mode or 5000 microseconds for
external mode (refer to Figure 2.7, Ionization Control tab). Click
Activate
Changes
. Alternatively, one can use segment 1 of
C:\VarianWS\4000Service\4000 MS (Int or Ext) Service.mth.
This is a quick check to confirm the absence of a m/z 28 signal. The m/z 28
signal should not be present due to the massive intensity of the 18/19 signal
before bakeout. Presence of a m/z 28 signal can indicate a leak or contaminated
gas.
Summary of Contents for 4000 GCMS
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