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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 4 on page 69 and Table 7 on page 69.
• Cool and vent the MSD, remove the GC column, and cap off the interface.
Using argon or other introduced gas to find air leaks 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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