66 5975/5977 Series MSD Operation Manual
3 Operating in Electron Ionization (EI) Mode
The MSD can be used to measure actual column flow. You inject a small
amount of air or other unretained chemical and time how long it takes to
reach the MSD. With this time measurement, you can calculate the column
flow. See “To Calibrate Column Flow Linear Velocity”on page 72.
Venting the MSD
A program in the data system guides you through the venting process. It turns
off the GC and MSD heaters and diffusion pump heater or the turbo pump at
the correct time. It also lets you monitor temperatures in the MSD and
indicates when to vent the MSD.
The MSD will be damaged by incorrect venting. A diffusion pump will
backstream vaporized pump fluid onto the analyzer if the MSD is vented
before the diffusion pump has fully cooled. A turbo pump will be damaged if it
is vented while spinning at more than 50% of its normal operating speed.
WARNING
Make sure the GC/MSD interface and the analyzer zones are cool (below 100 °C)
before you vent the MSD. A temperature of 100 °C is hot enough to burn skin; always
wear cloth gloves when handling analyzer parts.
WARNING
If you are using hydrogen as a carrier gas, the carrier gas flow must be off before
turning off the MSD power. If the foreline pump is off, hydrogen will accumulate in
the MSD and an explosion may occur. Read “Hydrogen Safety”on page 18 before
operating the MSD with hydrogen carrier gas.
CAUTION
Never vent the MSD by allowing air in through either end of the foreline hose. Use the
vent valve or remove the column nut and column.
Do not vent while the turbo pump is still spinning at more than 50%.
Do not exceed the maximum recommended total gas flow. See “5977B Series MSD
features”on page 14.
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