206 Agilent 7890 Series Troubleshooting
8 Troubleshooting Tasks
When to Change Gas Purifiers
Agilent highly recommends using purifying traps in the gas
lines to prevent impurities from entering and contaminating the
GC system or damaging the column. Some traps are
single-purpose for the removal of oxygen, moisture, or
hydrocarbons, while combination traps remove all those
contaminants.
The best way to know when it is time to change a trap is to use
an indicating trap, which should be placed after a high capacity
trap. Agilent recommends using glass indicating traps such the
Gas Clean Filter system, whose clear tubes display a distinct
color change in response to contamination. This color change
tells the analyst it is time to change traps.
If no indicating traps are used, it is best to follow the
manufacturer’s recommendation for replacement frequency.
Typically, the manufacturer will state how many gas cylinders
can be purified with a given trap. If desired, it is possible to
estimate when to replace the trap by performing a rough
calculation. For example: you have a standard “K” size cylinder
with He at 99.995% purity that contains 7,800 L of He. Assuming
a worst case scenario in which the remaining 0.005% is all
oxygen, you should have 39 mL, or about 56 mg of O2 in the
tank. Agilent’s OT3 oxygen trap, for example, has a capacity of
600 mg O2. Therefore, you need to replace the OT3 trap every 10
cylinders. This is just a rough estimate, and it is prudent to
change traps too early rather than too late.
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