Detector Systems
Electron capture detector (ECD)
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).
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