Troubleshooting; Chromatographic Symptoms - Agilent Technologies 7820A Service Manual

Troubleshooting

Symptom
Lost peaks
(degradation)
Lost or tailing peaks Valve or transfer line
Baseline
perturbation
Peak tailing broad
peaks
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Agilent 7820 GC Service
Most of the problems associated with sampling valves are
related to peak broadening in transfer lines and inlets, sample
adsorption by the valve or transfer lines, leaks, and perturbations
in the baseline.

Chromatographic symptoms

Troubleshooting valves and their related plumbing is primarily a
matter of systematic checking and verification of unimpaired
mechanical operation of any moving part. This requires an
understanding of how the valve functions internally and how the
plumbing is configured. A plumbing diagram is essential for
effective troubleshooting.
The following "symptom-cause" list gives the most commonly
encountered problems found with valves and their solution.
Possible cause
Valve or transfer lines
too hot
Transfer line activity
too cold
Slow valve rotation
Rotor distorted
Sample/column pressure
too
different
Column overload
Flow too slow
System voids
Solution
Reduce temperature 50 °C,
reevaluate
Use nickel or Hastelloy tubing
Increase temperatures 50 °C,
reevaluate
Increase actuator pressure
Replace rotor
Add back-pressure regulator
to sample drain
Use smaller sample loop
Increase split flow
Increase column flow
Increase split flow
Check connections
Reduce volume of connecting
tubing