HP 5890 Series II Plus Reference Manual page 205

Chromatographic Troubleshooting
Baseline symptoms
2. Noise increases gradually to an unacceptable level:
Contaminated detector gases (hydrogen and air).
Air currents from a fan or air conditioner blowing across the top of
the instrument may interfere with gas exiting from the detector.
This is a possible, though not very likely, cause of noise since
detectors are well protected. Switching off the air current source
or shielding the detector area identifies this problem.
An inadequately tightened collector on an FID or NPD generates
noise.
A contaminated detector results in noise.
This symptom indicates gradual buildup of the noise source,
rather than an abrupt change as discussed above. FI detectors are
susceptible to gradual buildup of deposits in the collector. In
extreme cases spiking occurs along with increased noise level.
Silicon dioxide deposits are formed when bleed from a silicone
column is burned in the flame. This material is removed
mechanically. Preventive measures include use of low column
loadings, stationary phases with high•temperaturelimit, thorough
column conditioning before use, and the lowest possible oven
temperatures for the analysis.
Carbon deposits may form from solvents that burn poorly
(primarily chlorinated materials and aromatics). If possible, avoid
such solvents. If they are necessary, periodic cleaning of the
collector is required.
Gradual noise increase may occur from saturated carrier gas drier
or chemical traps. When these approach their capacities,
contaminants begin to pass through and create noise. Trap and
drier regeneration or replacement eliminates this source of noise.
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