Problem with SCD help needed

[atasa88]

Dears!

This is a problem i'm facing for a long period of time: my SCDs show terribly unstable results, from run to run the signal either rises or falls although i inject the same gas or liquid, at the same conditions.

To be precise, I have three Agilent 7890A instruments with two channels on each, one for gas injection, another for liquid injection. So, there are SIX SCDs on three instruments. All the gas flows (Hydrogen and air as oxydizer) are EPC controlled and controlled by Dual Plasma Controller. And once all six SCDs started giving different result on the same gas or on the same liquid from run to run... There is no changes in retention times but there is a great difference in signal heights...

I would be grateful to any reply, please, who has an experience of working with SCDs?

[chemviren]

1) How long had the SCDs been running stable? (i.e. since initial install or tubes replacement)
2) Have you ever decoked your tubes by turning off the hydrogen to the DP burner?
3) Have you confirmed your hydrogen and/or oxidizer to the DP burner is not fluctuating? Sometimes an EPC can be faulty. What kind of EPC module are you using, PCM or Aux EPC?

[atasa88]

1) How long had the SCDs been running stable? (i.e. since initial install or tubes replacement)
2) Have you ever decoked your tubes by turning off the hydrogen to the DP burner?
3) Have you confirmed your hydrogen and/or oxidizer to the DP burner is not fluctuating? Sometimes an EPC can be faulty. What kind of EPC module are you using, PCM or Aux EPC?

Hmmm... thank you for reply, i did not ave an access to the internet for a long time...

1. they were stable for about a month, not more...
2. all the tubes are periodically replaced to exclude the possibility that the problem come from the burner
3. we are using Aux EPCs, and i think the flow of hydrogen can be fluctuating...