Agilent Technologies 5975T LTM GC/MSD, Руководство по устранению неисправностей и техническому обслуживанию

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50 Troubleshooting and Maintenance Guide
3
Chromatographic Symptoms
Noisy Signal, Including Wander, Drift, and Baseline Spikes
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.
Noisy baseline
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” on page 99.)
If noise appears suddenly on a previously clean baseline, do the
following:
• Consider recent changes made to the system.
• Bakeout the inlet. See the 5975T LTM GC/MSD Operation
Manual for this procedure.
• Verify the purity of carrier gases.
• Verify proper reassembly after recent maintenance.
• Inspect the ion source for contamination.
Total noise
Long-term noise (drift)
Wander
Short-term noise