Chromatography Forum

I noticed small jagged peaks that contained every mass programmed for scanning a number of times over the last month. I had been in contact with Agilent to try and determine the cause and get ahead of it but yesterday this noise became unmanageable. The instrument tunes fine - all connections have been checked and scanning in manual tune reveals nothing odd. But when I try and do a run this mess shows up randomly throughout the chromatogram.

Ran through some diagnostics with Agilent and they are recommending changing the electron multiplier at this point but it is only tuning to 1850 Ev and otherwise seems OK via the u_phonics test. Darkcurr macro for the HED also shows nothing out of the ordinary.

I was unable to post an image but the spectra look like a flea comb you'd use on your dog showing every mass or almost every mass. The random jagged peaks range anywhere in abundance from 10000 to over 10000000.

Anyone ever see this? If so what was the problem?

Hello

It sounds like dirty dynode. You can clean it with isopropanol.

Regards

Tomasz Kubowicz

Thank you. I will try that. I found a pdf for cleaning the dyode on the 5973. Hopefully that will be enough guidance to get me through it on the 5975.

Thank you. I will try that. I found a pdf for cleaning the dyode on the 5973. Hopefully that will be enough guidance to get me through it on the 5975.

Should be the same for the 5975, or very very similar.

We also had this problem, small random spikes of noise during a run. I had it on my 5975 but I can't remember for certain if cleaning the dynode solved it or changing a filament. It seems to me it was actually the filament that fixed our problem, it finally blew out and after the change the noise went away.

Agilent sent over a pdf for the 5975 on HED cleaning. I did go through the process and it seemed to improve somewhat but the sporadic nature makes it hard to be certain if there was an effect. Bottom line the noise is still there to the point where I can't do runs. On their advice I capped the MSD inlet and tried a run just to be absolutely sure this problem isn't related to a GC or column problem and that had no real effect. The latest uphonics test does show pretty good results with low STD's at all Ev's.

I did swap filaments early on in the trouble shooting on this and it had no effect.

So it looks like an HED or EM issue. With the uphonics test coming out decent and no apparent tuning issues it seems to lean more towards HED based on my current understanding. Agilent only sells the HED with a new EM in place so that looks like the best option to get this settled.

Replaced HED which came with a new EM as well - problem is gone