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General GC Maintenance
The common general GC maintenance tasks are checking and changing gas
supply cylinders, leak checking, and changing gas purifier filters. These
should be performed at the frequency suggested above. The following
procedures are critical to the successful long term operation of a Gas
Chromatograph. It is very important to leak check the system on a routine
basis and to ensure the quality of gas supplies, particularly the carrier gas.
Check and
Renew Gas
Supplies
The pressure of the various GC gas supplies should be checked on a weekly
basis and the following guidelines used for frequency of renewing supplies:
Carrier gas: The carrier gas supply cylinder should be changed when its
pressure drops below 200 psi. This ensures that high purity carrier gas is
always supplied to the instrument. With typical usage on one Gas
Chromatograph an A-size cylinder of carrier gas should last for three to six
months. Note that this usage includes also using the carrier gas as the supply
of make-up to the detectors. When a new cylinder is installed the regulator
and tubing should be purged with carrier gas before connecting to the GC.
This will avoid introducing a large amount of air into the GC.
Detector fuel gases: The typical detector fuel gases are hydrogen and air.
These should be changed when the supply pressure drops below 200 psi.
Typically an A size cylinder of hydrogen used on one GC with one Flame
Ionization Detector lasts about six months. However, due to the high flow rate
of air used in a Flame Ionization Detector this supply will need renewing more
frequently. For this reason it is worthwhile to consider a clean supply of
compressed air for FID equipped instruments.
Leak Check
Leak checking is one of the most important maintenance tasks that is carried
out on a Gas Chromatograph. The following information refers to general
leak checking procedures for the 3800 Gas Chromatograph. Specific
information regarding individual 3800 components will be presented in the
relevant part of this maintenance section.
Leaks in the GC system can lead to poor chromatographic performance or
damage components such as the analytical column. The presence of oxygen
in the GC carrier gas at elevated temperatures can lead to permanent column
phase degradation. While the use of an oxygen filter on the carrier supply to
the instrument can help, leaks downstream of the filter are generally more
likely to be the problem.
