Agilent Technologies 7890A Troubleshooting Manual page 38

3
Chromatographic Symptoms
Noisy Detector, Including Wander, Drift, and Baseline Spikes
Total noise
Long-term noise (drift)
Wander
Short-term noise
Noisy baseline
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Noise should be measured under "normal" operating
conditions, with a column connected and carrier gas on.
Noise typically has a high frequency component (electronic
in origin) and lower frequency components that are referred
to as wander and drift.
Wander is random in direction but at a lower frequency than
the short- term electronic noise. Long- term noise (drift) is a
monotonic change in signal over a period that is long
compared to the wander and electronic noise (see below).
Terms like "short" and "long" are relative to the width of the
chromatographic peaks.
A noisy baseline or high detector output can indicate leaks,
contamination, or electrical problems. Some noise is
inevitable with any detector, although high attenuations can
mask it. Since noise limits useful detector sensitivity, it
should be minimized.
• For all detectors, check for leaks at the column fittings.
(See "Checking for Leaks".)
• For the FID, see To Measure NPD Leakage Current.
• For the TCD, verify data collection at < 5 Hz.
If noise appears suddenly on a previously clean baseline, do
the following:
• Consider recent changes made to the system.
• Bakeout the inlet. See the following:
• To Bakeout Contaminants from the Split/Splitless Inlet
Troubleshooting