Chromatography Forum

Hello!

In advance, I apologize for my English (I am not a native speaker) and for being relatively new to the field of gas chromatography.
I have a problem with the GC CP3800 (FID, N2 carrier) in terms of column pressure. A few weeks ago, I turned on the GC and the system did not stabilize due to the high column pressure (normal: 11.4 psi, actual value: 24 psi). I turned off the system to check for contaminations. I started at the injection unit using acetone for cleansing and I could remove a lot of contamination. Also in the line (I guess it is the purge line) going off of the injector, I could find some residuals and was able to get the line clean again. Unfortunately, these cleansing procedures did not help very much to reduce the column pressure. Therefore, I cleaned the injector inlet and cut off a little part of the column which goes in the injector, also unsuccessful.

Let´s come to the very interesting part! When I turn off gas lines the system still displays a higher column pressure and even indicates a column flow (~1mL/min). How can this be possible?!

Any kind of help is highly welcome, as I am starting to become extremely desperate...

Regards
dp_OCII

Welcome to the forum.

From the symptoms you describe the most likely explanation is a faulty electronic pressure control that is not giving a correct reading. If you turn off the carrier gas supply to the GC, then loosen the septum nut on top of the inlet, does the pressure and flow indication drop to zero ?

Peter

Welcome to the forum.

From the symptoms you describe the most likely explanation is a faulty electronic pressure control that is not giving a correct reading. If you turn off the carrier gas supply to the GC, then loosen the septum nut on top of the inlet, does the pressure and flow indication drop to zero ?

Peter

Hello Peter,

thank you very much for answering. I just checked the indication after loosening the septum nut and the values do not drop to zero. I guess that the issue can be related to the EPC?
If yes, is there a way to fix the problem?

Regards
dp_OCII

I would try removing the filters in the supply lines to the EPC. The are small cylindrical filters in the left side of the instrument. I was having similar issues (pressure would not stabilize and I was having high pressure) and once I replaced these filters with dead volume connectors, the pressure stabilized and I have had zero issues since.

Good luck!

Welcome to the forum.

From the symptoms you describe the most likely explanation is a faulty electronic pressure control that is not giving a correct reading. If you turn off the carrier gas supply to the GC, then loosen the septum nut on top of the inlet, does the pressure and flow indication drop to zero ?

Peter

Hello Peter,

thank you very much for answering. I just checked the indication after loosening the septum nut and the values do not drop to zero. I guess that the issue can be related to the EPC?
If yes, is there a way to fix the problem?

Regards
dp_OCII

There should be a procedure to zero or initialize the pressure control - I am not familiar with your particular GC, so you will need to check in the users manual what the procedure is.

Peter