Agilent Technologies 6890N, Troubleshooting Manual

Page: 33 / 102

Chromatographic Symptoms
3
Troubleshooting 33
Noisy Detector, 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” .)
• 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
• To Bakeout Contaminants from the Purged Packed Inlet
• To Bakeout Contaminants from the COC Inlet
Total noise
Long-term noise (drift)
Wander
Short-term noise