56 Troubleshooting and Maintenance Manual
3 CI Troubleshooting
3 Check for tightness of seals at GC inlet and interface column nuts.
Ferrules for capillary columns often loosen after several heat cycles. Do
not overtighten the interface nut.
4 If any of the fittings inside the flow module (VCR fittings) were loosened
and then retightened, the gasket must be replaced. These gaskets are good
for one use only.
5 Remember that most small air leaks visible in CI mode are located in
either the carrier gas or reagent gas flow paths. Leaks into the analyzer
chamber are not likely to be seen in CI because of the higher pressure
inside the ionization chamber.
6 Half-split the system.
• Close valves starting at the gas select valves (Gas A, then Gas B), then
close the shutoff valve. See Figure 3 and Table 4.
• Cool and vent the MS, remove the GC column, and cap off the interface.
If you use argon or other introduced gas to find air leaks, this does not work
well for the reagent gas flow system. It takes as long as 15 minutes for the peak
to reach the ion source if the leak is at the inlet to the flow module.
Do not loosen the nuts on any VCR fittings unless you intend to replace the gaskets.
Otherwise, you will create an air leak.
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