71
Troubleshooting
6.4.7 Noisy baseline
Any baseline will have some noise or disturbances. To observe this, zoom into the
baseline section. Baseline noise becomes a problem when it interferes with the analysis.
Methods that have colored reagent solutions will be typically more noisy.
A noisy baseline may be easily noticed when running reagents only. In order to determine
whether it is a hardware or chemistry problem, it is necessary to put all the reagent lines
in deionized water and run at normal pump speed of 35. If the manifold has a column,
make sure it is bypassed. If after several minutes the noise goes away, the problem is
most likely related to the chemistry, specifically the reagents. If noise is present while
running deionized water, a hardware or a flow problem could exist. The flow problem may
be caused by the manifold tubing or any of the fittings (Figure 60).
6.4.7.1 Common causes of noisy baseline
Hardware or flow-related noise
• Pump tubes: Old pump tubes are a common cause of noise in the baseline.
Change all pump tubes once a month or when they are flattened.
• Blockages: Clogs and partial clogs may be present in the manifold or waste line.
Refer to section 6.5 on page 73.
• Injection valve: A malfunctioning valve could be responsible for flow fluctuations.
Refer to section 6.4.3 on page 68.
• Flow cell: Air could be trapped in the flow cell. Tap the flow cell to get rid of the
air. If the air seems to be stuck in the flow cell, place all reagent lines in a 1 M HCl
solution. Run the HCl solution for about 5 minutes. Place all the reagent lines in
deionized water and rinse for about 10 minutes. Make sure the flow cell is oriented
correctly (writing-side down), with the inlet at the bottom and outlet at the top.
• Peristaltic pump: The pump may be malfunctioning and varying the speed of the
rollers. Refer to section 6.11 on page 76 to check the pump.
Figure 60 Noisy baseline
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