198 Advanced Operation Manual
5 Detectors
• Keep the detector temperature high (320 to 335 °C).
• Turn the hydrogen flow off during solvent peaks and
between runs.
Turning hydrogen off during a solvent peak
When using the NPD, the baseline shifts after a solvent peak
and can take some time to stabilize, especially with
chlorinated solvents. To minimize this effect, turn off the
hydrogen flow during the solvent peak and turn it back on
after the solvent elutes. With this technique, the baseline
recovers to its original value in less than 30 seconds. This
also extends the life of the bead. The hydrogen can be
turned on and off automatically as part of a Run Table. See
“Run Time Programming” on page 12.
Turning hydrogen off between runs
To extend bead life, turn off the hydrogen flow between
runs. Leave all other flows and the detector temperature on.
Turn on the hydrogen flow for the next run; the bead will
ignite almost immediately. The process can be automated
with Run Table entries.
Turning off the detector
Setting the initial bead voltage for new beads
Before you turn on the bead for the first time, manually set
its voltage to a safe value so that the new bead is not
destroyed.
1 Make sure Adjust Offset is turned Off.
2 After the temperature stabilizes at setpoint, set the initial
Bead Voltage, depending on bead type:
• Blos bead: 0.0 V to 0.5 V
• Ceramic bead (white or black): 0.0 V to 2.0 V
If you turn Adjust offset [Off] at any time, the bead voltage,
hydrogen, and air flows all turn off.
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