M
AINTENANCE
General GC Maintenance
CP-3800 GC Getting Started Manual
51
The carrier gas should first pass through a hydrocarbon trap, then an
indicating moisture filter, then a high capacity oxygen trap and finally through
an indicating oxygen trap. As moisture reduces the effectiveness of an
oxygen trap, a moisture trap should always be placed in front of an oxygen
trap. When the indicating oxygen trap begins to change color, the high
capacity oxygen trap should be changed immediately. The moisture trap
should also be changed immediately when it changes color to prevent
breakthrough of moisture to the oxygen trap.
The minimum recommended carrier gas purifier configuration is a combined
moisture / hydrocarbon trap. This configuration can be used with routine GC
analyses using FID, TCD, TSD and PFPD detectors. If an ECD or mass
spectrometer is being used, an indicating oxygen trap should also be added.
For trace analysis the combination of hydrocarbon trap, moisture trap and
oxygen traps should be used.
Use the following procedure to install or replace a carrier gas purifier on the
3800. Gas purifiers supplied by Varian and most other chromatography
suppliers are equipped with 1/8
″
Swagelok fittings. This facilitates easy
removal and replacement of purifiers. In addition gas purifiers are sealed at
both ends for protection. Purifiers should only be uncapped when you are
about to install them.
1
Turn off the carrier gas supply at the input regulator. Note the
operating pressure to allow resetting to this value after the purifier is
installed.
2
Carefully open the carrier gas fitting at the inlet bulkhead to the GC
or the existing carrier gas purifier. Wait for the release of carrier gas
pressure before removing the fitting.
3
Identify the recommended direction of carrier gas flow on the purifier.
This is normally indicated by an arrow on the side of the purifier.
Remove the inlet cap from the purifier and immediately connect the
carrier gas inlet line to the purifier inlet.
4
Remove the outlet cap from the purifier, turn the carrier supply back
on and allow the carrier gas to purge through the purifier for 0.5 - 1
minutes.
5
Connect the outlet of the gas purifier to the inlet of the GC or the inlet
of the next purifier, if used. If a new connection is being made, use
chromatography grade copper tubing and new Swagelok fittings.