88
Agilent 7820 GC Service
It may take 24 hours for the uECD baseline to
completely stabilize, especially if you are
starting with a cold system and want to assure
high-sensitivity operation. Therefore, for the
most accurate results, run the detector at normal
operating conditions for as long as possible (at
least 2 hours and up to 24 hours) before running
the frequency test.
If you will be injecting into an unused inlet, you
must use low-bleed septa. Make sure to condition
new septa before use in an inlet for several hours
with 1 to 5 mL/min carrier flow.
1 Make sure you are using normal operating conditions and
that at least 2 hours have elapsed since the last run.
Turn on the uECD and the corresponding signal.
Check the displayed "Output":
 <25 = uECD frequency is acceptable
 ≥1000 = Contaminants in system
Each display count equals a frequency of 1 Hertz
(e.g., a display reading of 100 = 100 Hz.).
If the uECD frequency indicates contamination (≥1000) check for
the following:
 Contaminated carrier gas trap(s) and or supply—replace
carrier gas supply tank and any traps on the carrier supply
line.
 Insufficient column conditioning—fully condition the
column.
 Contaminated detector—bake out the detector.
 Column, inlet and/or septum bleed—clean the
inlet/replace the septum with a conditioned, low bleed
septum.
 Leaks—perform leak tests on both the inlet and detector
systems.
 Anode current leakage—make sure the anode contacts
are clean. Make sure the anode nut is tight.
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