520 Gases
Cryogenic cooling requirements
10 of 14
Jun 2001
Site Preparation
Agilent 6890 Gas Chromatograph Service Manual
Using carbon dioxide
WARNING Pressurized liquid CO
2
is a hazardous material. If CO
2
escapes its container,
it exits at high pressure and low temperatures that can be dangerous to
personnel. CO
2
in high concentrations is toxic to humans. Consult your local
supplier for recommended safety precautions and delivery system design.
Caution Liquid CO
2
should not be used as a coolant for temperatures below –40°C
because the expanding liquid may form solid CO
2
—dry ice—in the GC oven. If
dry ice builds up in the oven, it can seriously damage the GC.
Liquid CO
2
is available in high-pressure tanks containing 50 pounds of liquid.
The CO
2
should be free of particulate material, oil, and other contaminants.
These contaminants could clog the expansion orifice or affect the proper
operation of the GC.
Additional requirements for the liquid CO
2
system include:
• The tank must have an internal dip tube or eductor tube to deliver liquid
CO
2
instead of gas (see Figure 520-4).
• The liquid CO
2
must be provided to the GC at a pressure of 700 to 1,000 psi
at a temperature of 25°C.
• Use 1/8-inch diameter heavy-wall stainless steel tubing for supply tubing.
The tubing should be between 5 to 50 feet long.
• Coil and fasten the ends of the tubing to prevent it from “whipping” if it
breaks.
• Do not install a pressure regulator on the CO
2
tank, as vaporization and
cooling would occur in the regulator instead of the oven.
• Do not use a padded tank (one to which another gas is added to increase
the pressure).
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