Using Liquid Nitrogen - Agilent Technologies ALS Handbuch

7890 Series GC Site Preparation

Using liquid nitrogen

Liquid nitrogen is a hazard because of the extremely low temperatures and high
WA R N I N G
pressures that may occur in improperly designed supply systems.
Liquid nitrogen can present an asphyxiant hazard if vaporizing nitrogen displaces
oxygen in the air. Consult local suppliers for safety precautions and design
information.
Liquid nitrogen is supplied in insulated Dewar tanks. The correct type for
cooling purposes is a low-pressure Dewar equipped with a dip tube—to deliver
liquid rather than gas—and a safety relief valve to prevent pressure build-up.
The relief valve is set by the supplier at 138 to 172 kPa (20 to 25 psi).
If liquid nitrogen is trapped between a closed tank valve and the cryo valve on the
WA R N I N G
GC, tremendous pressure will develop and may cause an explosion. For this reason,
keep the delivery valve on the tank open so that the entire system is protected by the
pressure relief valve.
To move or replace a tank, close the delivery valve and carefully disconnect the line
at either end to let residual nitrogen escape.
Additional requirements for the liquid N
• Cryogenic cooling with Liquid N
• If needed, set the liquid N
• Make sure the supply tubing for liquid N
• Situate the liquid nitrogen tank close (within 1.5 to 3 m, or 5 to 10 feet) to
54
30 psi). Follow the manufacturer's directions.
refrigeration and air-conditioning lines is suitable for insulation. (Foam
tubing insulation is not supplied by Agilent. Contact a local supplier.) Since
pressures are low, insulated copper tubing is adequate.
the GC to ensure that liquid, not gas, is supplied to the inlet.
system include:
2
requires 1/4-inch insulated copper tubing.
2
pressure to the GC at 138 to 207 kPa (20 to
2
is insulated. Foam tubing used for
2
GC, GC/MS, and ALS Site Preparation Guide