[BuiThuy]

I use an HP 5890 series II as online-GC. I opened and cleaned the multi-port- valve, injector and detector.
After cleaning, the sig.1 shows the value from 15360 to 28160 when the temperature increase from 40 ° to 240°C. This value depends linearly on the temperature, it is stable when the temperature is constant.
I set the baseline at 15360 and increased the temperature, the sig.1 increase and when it reachs to the value of about 17000 the signal in screen (chromatogram) reachs to 1 V (the upper limit) and is cut.
Normally, after cleaning some dust can come in to the column and the sigal is high but it is not so high as this time and it goes down gradually. Another thing: when I opened the detector to clean I saw a lot of water in it.
I think about the leak, but I saw the buble at the end of the column. Today I want to check the detector again but it can only be cooled down it to 160°C while yesterday it could go down to 60°C

Please show me the reason and the solution.

Thanks a lot

[Dude]

A typical signal on an Agilent (formerly HP) GC is about 10 mV.  You should be able to control the temperature of the detector using the keypad.  If you can't, unplug - wait 10 seconds and then turn on.

My approach.

1.  Disconnect the column from the detector and observe if the signal drops.
     A.  If the signal drops, the contamination is likely coming from the column or carrier gas.  Replace the column.
     B.  If the signal stays approximately the same, you didn't clean the detector well enough.  You might have to    do this again anyway if you have to change the column.

If neither works, call the technical service department at Agilent for further advice/needed parts.

[BuiThuy]

Thank you very much, Dude
I have disconnected the multi port valve so now it is a normal GC but the signal is not drop. Therefore, I think the problem comes from the GC.
I can now decrease the temperature of the detector. Last time I did not decrease T of the column, so the heat column tranfer to detector by gas.
Your idea is very reasonable, I will do it.