Chromatographic Symptoms 3
Agilent 7890 Series Troubleshooting 81
NPD Response Low
• Perform complete inlet maintenance: Replace all consumable
parts and bake out the inlet.
• Perform column maintenance: Bake out contaminants as
needed. Verify correct column installation.
• A large concentration of solvent has extinguished the
hydrogen/air plasma. Increase the bead voltage. Run the
makeup gas at a flow rate of 5 mL/min.
• Verify that there is hydrogen coming from the external
supply. Check that flow and pressure are turned on at the
keyboard. The hydrogen flow rate should be between 1.0 and
5.5 mL/min. Measure the actual gas flow at the detector. (See
“To Measure a Detector Flow”.)
• Check for a partially plugged jet. See To Check for a Plugged
FID Jet.
• If the upper ceramic insulator is contaminated, a high offset
(2 to 15 pA or more) will occur when the bead is off. This
directly affects sensitivity. Replace the ceramic insulator.
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