PDA-100 Photodiode Array Detector
4-4
Doc. 031644-02 9/03
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Plot scale exaggerates baseline noise
If autoscale is selected, even a plot with low noise may fill the screen. Check
the Y-axis values.
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Air bubbles in flow cell
Remove the trapped air (see Section 5.3).
To prevent air from becoming trapped in the cell, follow these steps:
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Degas mobile phases and post-column reagents by vacuum degassing
or sparging with helium.
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Connect a backpressure line to the cell (see Section B.3.2). This
increases the backpressure, thereby shrinking bubbles and allowing
them to pass more easily through the cell.
•
Contaminants in flow cell
Clean the cell (see Section 5.2).
If a UV wavelength is selected, make sure the deuterium lamp is on. If a
visible wavelength is selected, make sure the tungsten lamp is on.
•
Deuterium lamp is dimming
The light output of the deuterium lamp decreases over time. The lower light
output may increase noise above an acceptable level, especially after the lamp
has been in service for more than 1000 hours. If this occurs, replace the lamp
(see Section 5.7).
•
Tungsten lamp needs replacement
Install a new tungsten lamp (see Section 5.8).
•
Lamp incorrectly installed
Make sure that both lamps are fully seated in the optical bench. See
Section 5.7 or Section 5.8 for installation instructions for the deuterium lamp
or tungsten lamp, respectively.
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Inappropriate reference wavelength
Select a reference wavelength in a quiet area of the spectrum where little
absorption occurs. Dionex recommends selecting a reference wavelength
below 380 nm for UV applications and above 600 nm for visible applications.
For more information, see Section 3.4.
