Chromatography Forum

Hi all,

My filament in my Agilent GC/MS 5975 has recently burnt out. I replaced the filament and did source cleaning at the same time. After assembling everything back to the GCMS, I performed an autotune. Strange things happen here. My mass 69 has dropped from 400000 to 30000. I noticed the peak for mass 502 has a split peak. the repeller voltage went up from 25 to 35. The ion focus voltage has dropped from 90 to 57. The entrance lens voltage has dropped from 25 to 12. The EM Voltage went up from 2200 to 2800. The air/water check is normal. They are all below 1%. Therefore, no leak. I recleaned the souce after. However, the same thing happen. Anyone can give me indication of the problem?

Thanks!

There are probably a lot of things that can cause these symptoms, but the stupidest thing I managed to do when source-cleaning and replacing filament was to put the source back in with the orange and blue wires that go to the lenses at the back of the source routed so that they fouled the entrance for the column when I closed the source again. Not good.
It's also worth making sure you've got those two connections the right way round (blue at the back).
Otherwise, when source cleaning you have to make sure you don't damage any of the insulators, and you shouldn't be cleaning them particularly ferociously (no sonicating in solvent etc.; just wipe off any obvious dirt), and I've heard it's worth taking a quick look at the filament after fitting it, to make sure that nothing is shorting it to anything.

Yep, the orange-blue switch was the first thing I thought of as well.

The repeller insulators are pretty fragile; perhaps one or both have cracked?

Thanks everyone!

I have double checked the orange and blue cable connections. Would that be an indication of a failure Electron Multiplier? Anyway, I might have to call a service technician to come in.

What is your high vacuum reading now?

You may want to hit the quads with a little compressed air, I once found a piece of lint had gotten onto my quads and made thing go weird. That split 502 peak does make it seem like something with the quads. How are your peak widths? Any fronting on the peaks in profile scan? Or fuzzy tops on the peaks in profile scan?

The multiplier is quite high, even the before was a little high, but that shouldn't cause problems with the splitting of peaks.