Gas Chromatography High Baseline

Discussions about GC and other "gas phase" separation techniques.

3 posts Page 1 of 1
Good day all,

I'm asking for help about the unusual high baseline of the front detector of our 7890 GC System. Our system was installed with 2 detectors and is capable of running dual analysis with Ar and He as the carrier gases.

Last June 2018, the front detector(He carrier gas) had an issue and was giving off an erratic output. It was then fixed by a service engineer and replacement parts were installed (motherboard, detector, signal board). These replacement parts were not new and was taken from a laboratory from another site but they were in good working condition.

After installation, the TCD Front Signal was no longer erratic but the baseline was now high. The baseline jumped from 15uV to 280-300uV and it gave a wandering signal.

We tried baking and conditioning the whole system overnight to remove any contamination/impurities that could be present but the baseline remained at 280uV. The oxygen filter was also replaced with a new one. Leak checks were done and no leaks were found.

Any idea on what could be causing the problem?
Thank you.
Hi & welcome to the forum.

I suggest to start by isolating the problem. Cap off the detector and check the baseline. If it's OK, problem is coming from the GC, if not, it's the detector.
You cannot cap off an Agilent TCD. The way they work is the column provides 1/2 of the flow for the switching. (I guess you could but you would have to jack up the make-up....)

Sounds to me more like you have a flow imbalance between the column and the reference. If you have a flow meter, turn off the filament (shuts off the reference) and measure the flow which should be carrier plus make-up. Then turn the filament back on and you should have about 2-3 times the reference flow that you do carrier. If not, you might want to adjust reference to this range and see what the baseline does at that point.

Best regards,

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