Detector Systems
Both detector baseline and sensitivity change with carrier flow rate due to change in temperature of the active element. This is the reason for the baseline drift in pressure•controlledinlet systems (capillary inlets) when temperature•programmingthe column. The amount of change in the detector response is proportional to the ratio of the total column flow change (temperature sensitive) to the makeup gas flow (not temperature sensitive), i.e., total column flow change divided by makeup gas flow. Element power should be adjusted after any change in carrier flow rate.
Septa should be checked for leaks daily or replaced regularly. An upward baseline shift at injection is often due to a leaky septum.
Caution Turn the detector off to avoid damaging the active element before changing septa.
When the detector is first turned on, its sensitivity and signal level change slowly over several hours. Therefore, for applications requiring very stable operation, leave the detector on overnight, lowering oven temperature to prevent contaminating the active element with column bleed.
To preserve the active element lifetime, it is good practice to reduce the power to the active element whenever the detector will not be operated for extended periods of time (such as over the weekend). To determine the proper amount of power reduction, plot the normal offset and note the displayed zero value
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