186 Agilent 7890 Series Troubleshooting
8 Troubleshooting Tasks
To Check or Monitor Split Vent Line Backpressure
Agilent provides a built-in test that measures backpressure in
the split vent trap and line for the split/splitless, multimode,
PTV, and VI inlets. The test measures the pressure developed in
the split vent flow path at a given, user-selected flow rate. This
flow rate can be your method Split flow setpoint, or the default
400 mL/min used by Agilent to compare “typical” values.
By running the test on a clean system, you can establish a
baseline for expected backpressure in the split vent line. Then,
you can re-run the test periodically to determine whether or not
the trap needs to be replaced before it impacts your
chromatography.
The pressure measured by the test depends on:
• The liner installed
• The flow rate used
Therefore, the actual measured value will vary between
different setups and from GC to GC.
The test checks for:
• Liner restriction
• Contamination on the gold seal (split/splitless inlet only)
• Restrictions in the split vent line, such as condensed sample
contamination in the split vent line and trap
The test can also provide a measure of suitability for the
installed hardware. Run the test using your method’s setpoints
and hardware. If the measured test pressure is close to the
desired column head pressure, this means that even a minor
amount of restriction in the split vent line can cause the GC to
become not ready. You may wish to install a different liner or
adjust the method. (For splitless liners, first try reinstalling the
liner. Splitless liners create more backpressure than split liners,
and so minor variations in orientation can make a difference at
low head pressures.)
To set a warning limit for the inlet trap check
To use the inlet trap check to monitor the split vent trap:
1 If the existing split vent trap has been used for many sample
injections, replace it. Make sure that the GC is clean:
• Replace inlet hardware if needed.
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