Drifting Baseline - Hach QC8500 Series 2 User Manual

Troubleshooting

6.4.8 Drifting baseline

6.4.8.1 Common causes of drifting baseline
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Electronic noise
Electronic noise can be identified by the insertion of an empty and clean flow cell in
the detector, as well as an interference filter. Do not pump any reagents at this time.
Run any worksheet to see the baseline on the screen. If the baseline is noisy when
there are no reagents going through the flow cell, the detector may be faulty or the
light bulb may be causing the problem. For instruments with more than one channel,
test the other detectors for noise. Call the manufacturer if electronic noise
is suspected.
Chemistry-related noise
Reagents: One or several reagents may have suspended particles. Make sure the
reagents are in solution completely. The reagents may also be old or contaminated.
Note: Some chemistries have a slight noisy baseline due to the color of the reagents. Examples
are: alkalinity, hardness, chloride, etc. This noise is normal.
Figure 61 shows a drifting baseline.
Figure 61 Drifting baseline
• Old chemical or reagent: An old reagent may cause a drifting baseline. The reagent
may have been made hours before the analysis, but the chemicals used to make it
may be very old.
• Flow problem: One of the pump tubes may not be clamped properly. Make sure that
the pump tubes are clamped down according to the instructions in the System
Operation manual. Blockages may also cause a drifting baseline. Make sure the
waste line is freely dripping.
• Contamination: One of the reagents and/or carrier is contaminated. With some
chemistries (Ammonia, TKN) it is possible the reagents may be absorbing the
contamination from the air. Place parafilm on the reagent and carrier containers.