Figure 9 -
Trap recommendations, order, and installation tips.
Hints for Using Traps:
l
Install close to GC bulkhead fitting.
l
Install vertically.
l
If using a high capacity, non-indicating 02 trap, use a low
capacity indicating trap after it.
Trap Recommendations:
Carrier gas:
oxygen, moisture, and hydrocarbon (optional)
Make-up gas:
none required*
Air (FID, etc.):
hydrocarbon (when trace oils are suspected)
H2 (FID, etc.):
none required
ELCD reaction gas:
hydrocarbon
* Use oxygen and moisture traps on
ECD
make-up gas.
Should purifiers be used for other gases?
In addition to carrier gas, traps can also be used for other
gases such as make-up and detector gases. Make-up gas for
Flame IonizationDetectors (PID) does not require purifica-
tion unless thePID is operated at high sensitivities. However,
oxygen andmoisture traps are highly recommended for
make-up gas when operating sensitive detectors such as
ElectronCaptureDetectors (ECD). The hydrogen reaction
gas used for sensitive Electrolytic Conductivity Detectors
(ELCD) also requires a hydrocarbon trap to remove trace
impurities. These impurities can cause baseline instability and
decrease the lifetime of the nickel reaction tube.
Many analysts use “house” compressed air from oil based
compressors which can emit hydrocarbon vapors. Trace oil
vapors can increase the background noise and contaminate
PID detectors. A new compressed air trap (cat.# 20637) is
availablewhich reduces oil vapors to levels less thanSppm.
This trap changes color as oil vapors are detected to indicate
when the trap is depleted. Because of its plastic body, the
Compressed air traps change colors to indicate oil contamination.
indicating compressed air trap is not recommended for carrier
gas lines.
After running the gas supply lines to the lab bench, it is time
to plumb the gas supply lines to the GC. Special care should
be taken to connect the correct gas type to the appropriate
fitting on the GC. The gas inlets for the GCwill be located in
different places depending on themake andmodel of your
instrument. Refer to your installation manual for the location
of the gas inlets.
Hints forECDs: Always uses high puritymoistme traps like our 1/8" “S” trap (cat.# 20686)
and 1/8" high purity oxygen trap (cat.# 20624) on ECD carrier andmake-up gas lines.
t
1
Traps are Necessary for Split Vents to Prevent
Breathing Air Contamination
Potentially hazardous or carcinogenic chemicals can enter the
lab atmosphere through the split vent in a capillary GC. As
much as 99% of the sample injected vents to the airwhere
chemists working nearby breathe these pollutants. This
problem is furthermagnifiedwhenmultipleGCs are used in
the same lab. Split vent traps, packed with charcoal, reduce
the uncontrolled release of hazardous materials into the lab.
The best trapping material is activated coconut charcoal due
-
10
10
1998
