7.1.1.c.  Vacuum Chamber.  As helium enters the MS unit, it must be evacuated to minimize secondary collisions with the ionized analytes.  Two vacuum pumps are used to accomplish this.  First, a rotary vacuum pump evacuates the gases to approximately 10-2 torr.  Then a molecular turbo pump reduces the pressure to 10-4 to 10-6 torr.

 

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