Nitrogen Phosphorus Detector (Npd) - Agilent Technologies gc/ms series Maintenance Manual

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Nitrogen Phosphorus Detector (NPD)

Bead Maintenance
NPDs are temperamental and require frequent maintenance. Small changes in any
of a number of parameters can significantly change the performance characteristics
of an NPD. The bead requires the most maintenance. It needs to be changed frequently,
thus a spare is a necessity.
The beads have to be kept dry which limits their storage life to about six months.
When a new bead is installed, slowly raise the detector temperature and bead current.
Rapid heating can crack or break the bead especially if it has been stored under humid
conditions. It has been observed that higher hydrogen flows and bead currents decrease
bead life. If the NPD is not in use, the hydrogen flow and bead current should be reduced
or turned off to increase bead life. Make sure there is some type of gas flow in a heated
detector or when there is current to the bead.
Bead Life
To extend the life of the bead:
• Avoid polar stationary phase, if possible.
• Use the lowest practical adjust offset or bead voltage.
NPD bead
• Run clean samples and keep the inlet/liner clean to minimize contamination.
• Turn off the bead when not in use.
• Keep the detector temperature high (320-335°C).
• Turn off the hydrogen flow during solvent peaks and between runs.
• If the NPD is off for an extended period of time in a high humidity environment, water
may accumulate in the detector. To evaporate this water, set the detector temperature
to 100°C and maintain it for 30 minutes. Then set the detector temperature to 150°C
and maintain it for another 30 minutes.