Chromatography Forum

Hi,

Can anyone help me with a baseline/detector issue? I am running Pesticides and PCB on an Agilent 7890B GC with dual ECD's. Five days ago my output value jumped from 192 to 32,000. I don't know why. I have baked everything on the instrument and the value went down to 4000. I ran PEM and CCV overnight and this morning the value was at 440,000. When the detector temperature is below 100 the value starts to go down but when I increase it to 330 the value jumps back up to 440,000.

Also, I run a DDT/Endrin breakdown check. Both the endrin and DDT breakdown is above 60%. Our requirement is <15% breakdown. I have cleaned out the inlet, changed the liner and septa. A new column was put in a few weeks ago. I clipped the new column. I checked for leaks and nothing. The breakdown is still high.

Has anyone had a similar problem? Or can anyone provide me some things to try?

I'd appreciate any help you can give.

For the DDT/Endrin breakdown you may need to clean or replace the split line. It is the copper line from the injection port to the split vent trap. When it becomes highly contaminated it can cause breakdown at the injection port.

We had a similar problem with the ECDs recently, and the solution was to have the ECD Anode cleaned. Ours would stay with a background signal at least 3000 and sometimes would max out and stay there for a day. The clean anode now has background near a normal 100-300.

Hello

For uECD check graphite ferrule (for makeup adapter assembly). It could be smashed and that is why you see high signal when oven temperature goes up - hot air from oven enters uECD through it.
I'd replace ferrule and uECD liner as well.

Regards

Tomasz Kubowicz

I'm betting on a leak somewhere. I've had the small ss tubing's weld fail on make up fittings. If you continue with those detector readings the detectors will suffer.