Peak Areas Not Repeatable - Agilent Technologies 7697A Troubleshooting Manual

2
Chromatographic Symptoms

Peak Areas Not Repeatable

20
Poor area count reproducibility results from changes in the
amount of sample reaching the GC detector. Check these
general areas:
• Check for inconsistent sample preparation technique,
including vial cap seals.
• Check the GC.
• If possible, mount an automatic liquid sampler (ALS)
over the inlet and inject a sequence of internal or
calibration standard directly into the inlet. Check the
area count reproducibility. If acceptable, check the HS.
If unacceptable, the problem is in the GC.
• If the problem is in the GC, refer to the GC's
documentation for troubleshooting procedures.
• Check sample vial size. (The HS cannot distinguish
between 20- mL and 22- mL vials.)
• Check the HS sequence log, event log, and status displays
for messages. Especially check the sequence log for
method deviations and dynamic leak check failures.
• Run replicates of known standards to verify the problem.
• Enable dynamic leak checking. This feature verifies that
each sample vial is leak- free.
• If not enabled, check the sample vial for cracks or
other leaks. See the
• If using dynamic leak checking, make sure the entered
leak rate is appropriate for the sample and its
preparation technique.
• Poor choice of equilibration temperature or time. For the
best reproducibility, the analytes in the sample and in the
headspace of the vial must reach static equilibrium.
Increase the equilibration time and/or increase the
equilibration temperature.
• Try shaking the sample to improve equilibration time.
• Check sample loop size. If the installed sample loop is
actually bigger than the configured sample loop size,
precision may suffer. The vial headspace pressure may not
be sufficient to repeatably fill the loop.
Operation Guide.
Agilent 7697A Troubleshooting