Detector Systems
Electron capture detector (ECD)
141
Background level
If the ECD system becomes contaminated, whether from impurities in
the carrier (or makeup) gas, or from column or septum bleed, a significant
fraction of detector dynamic range may be lost. In addition, the output
signal becomes noisy.
To check background level, allow ample time for components from
previous analyses to be flushed from the system, and then make a blank
run (one with no sample injected).
Prior to the run, enter the following:
DET A
(or
B
)
ON
SIG 1
(or
SIG 2
)
A
(or
B
)
Pressing
SIG 1
(or
SIG 2
) again displays the signal source assigned to
the particular output channel.
Ideally, the value displayed should be within the range 10 to 40 (100 to
400 Hz), indicating a clean system. For trace•levelanalysis, a reading of
20 to 60 is recommended. A large value of more than 50 (500 Hz)
indicates a contaminated system and thermal cleaning should be
performed (see Chapter 8, Preventive Maintenance).
