Chromatography Forum

I am currently running a 7890A GC in connection with a 5975C MSD. My problem is that the temperature setpoint for the front inlet keeps fluxuating so the run will not start. The GC itself has no problem coming up to the set temperature but the setpoint itself keeps changing. The front inlet pressure is also fluxuating. The fluxuation is minimal (0.003 psi) but enough so that the GC will not hold calibration long enough to start the run. I bleieve the issue lies more with the temperature setpoint than the pressure. My thought process was that the GC setpoint temperature kept fluxuating so the pressure would also change with it.

Method Setup
pulsed splitless injection
Front Inlet: 290 degrees. 8.1168psi
Oven: Initial temp 60 degrees hold for 0. Ramp 25 to 130 degrees hold for 0. Ramp 30 to 240 degrees hold for 0. Ramp 25 to 310 degrees hold for 8 minutes.

Steps that I have done to try to correct the problem
I have checked the front inlet and the column for leaks and none were present.
I have cleaned the injector port. the port itself is new and should not need replacing.
I have restarted chemstation
I tried to load the default method to see if the current method we are running is corrupted.
I have replaced the column nut, reducing nut, splitless disk and other routine maintenance.
I looked up Agilent's manual and tried to zero the calibration for the front inlet pressure, flow, and septum purge.
I followed the manual as best I could so if someone thinks this may be the problem I will be more than willing to try and zero again.

If there are any questions please don't hesitate to ask. Any help/advice would be much appreciated as I am still learning the ins and outs of the GCMS.

Thanks,
Steven

1-800-227-9770

Is it possible that when the injection port was replaced (you said it was new) that the insulation was not completely replaced? If there is no or not enough inslulation around the injection port to seperate it from the oven, the oven temp at the initial temp will interfere with the injection port temp through the opening in the oven and will cause the temp fluctuations you are experiencing. Set your oven temp to 250 degrees and if the inlet temp is stable, you'll know it's an insulation problem. Also, make sure the insulated cover that goes over the injection port nut in the oven is in place. You're correct, the pressure fluctuations are due to the temp change.

If it is an MMI inlet installed in 2010, check with Agilent about the inlet controller board. Some of those boards had problems. Mine gradually lost its ability to measure temperature. (Room temperature was -107 degrees, pretty good without the cryo connected)
The 3 connector board from Gerstel was replaced with a 2 connector Agilent board.

Thanks for the quick replies. I have been away from the office the past few days and haven't had a chance to respond. The issue seems to be the insulation around the inlet. I opened the port back up and the insulation sleeve was cracked.