Varian 4000 GCMS, Installation Procedures Manual

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2.3 Checking for High Mass Noise
Before baking out the system it should be checked for high mass noise (HMN).
NOTE: This check for HMN may not give usable results until after auto tuning the
system.
On the Full Scan Parameters tab in Manual Control (refer to Figure 2.9) enter a
Mass Range of 50 to 1000 m/z. On the Ionization Control tab turn off the fixed
ion time option (turned on in section 2.2) by un-checking the Fixed Ionization
Time check box (refer to Figure 2.7) and click
Activate Changes
. Alternatively,
one can use segment 2 of the C:\VarianWS\4000Service\4000 MS (Int or Ext)
Service.mth. Turn on the trap and click on the words
Ion Source
to turn off the
ion source. The RF and Multiplier should remain on (green is on, black is off). In
this configuration (refer to Figure 2.9) the Base Amount (monitored in the upper
right corner of the spectral window) should equal 1 or 2. In addition, no spiking
above the baseline should be observed. If the Base Amount is significantly > 2
and spiking is observed, the system should be shut down and trap should be
blown free of debris using a compressed inert gas. In a persistent case, the trap
cavity may require repeated efforts to free it of debris. If so, the surrounding area,
including the vacuum manifold and the center tube of the transfer line may also
need to be blown free of debris using a compressed inert gas.