1Introduction
Precautions
24 5977C GC/MSD Operating Manual
Precautions
Take the following precautions when operating a a GC/MSD system with
hydrogen carrier gas or when operating the MSD with the JetClean option that
supplies hydrogen from an MFC located on the MSD.
Mass spectrometer
automated shutoff
valves closed
Some mass spectrometers are equipped with automated diffusion pump shutoff valves. In these instruments,
deliberate operator action or various failures can cause the shutoff valves to close. Shutoff valve closure does not
shut off the flow of carrier gas. As a result, hydrogen may slowly accumulate in the mass spectrometer.
Mass spectrometer
manual shutoff
valves closed
Some mass spectrometers are equipped with manual diffusion pump shutoff valves. In these instruments,
the operator can close the shutoff valves. Closing the shutoff valves does not shut off the flow of carrier
gas. As a result, hydrogen may slowly accumulate in the mass spectrometer.
GC off A GC can be shut down deliberately. It can also be shut down accidentally by an internal or external failure.
Different GCs react in different ways. If an 8890 or 9000 Series GC equipped with Electronic Pressure
Control (EPC) is shut off, the EPC stops the flow of carrier gas. If a GC’s carrier flow is not under EPC
control, the flow increases to its maximum. This flow may be more than some mass spectrometers can
pump away, resulting in the accumulation of hydrogen in the mass spectrometer. If the mass spectrometer
is shut off at the same time, the accumulation can be fairly rapid.
Power failure If the power fails, both the GC and mass spectrometer shut down. The carrier gas, however, is not
necessarily shut down. In some GCs, a power failure may cause the carrier gas flow to be set to maximum.
As a result, hydrogen may accumulate in the mass spectrometer.
Table 4 Hydrogen accumulation mechanisms (continued)
Mechanism Results
Once hydrogen has accumulated in a mass spectrometer, extreme caution
must be used when removing it. Incorrect startup of a mass spectrometer
filled with hydrogen can cause an explosion.
After a power failure, the mass spectrometer may start up and begin the
pumpdown process by itself. This does not guarantee that all hydrogen has
been removed from the system, or that the explosion hazard has been removed.
You must remove the plastic cover over the glass window on the front of a
5977C Series MSD. In the unlikely event of an explosion, this cover may dislodge.
You MUST make sure the top thumbscrew on the analyzer side plate is fastened
finger-tight. Do not over tighten the thumbscrew; this can cause air leaks.
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