Chromatography Forum

I’m working on a 5973. I made some repairs to the gc (6890). I brought everything back up, got a nice tune, and returned to service. The customer was running and half way through, lost signal from the msd. There are no error messages. It won’t pass a tune now. I ran manual tune, changed parameters (em gain, lenses, etc.) and can see that this has an effect. I measured HED volts, 10K. It is intermittent. The ions look poorly formed (pftba), chopped up. I did switch filaments. Any ideas?

Dave

I’m working on a 5973. I made some repairs to the gc (6890). I brought everything back up, got a nice tune, and returned to service. The customer was running and half way through, lost signal from the msd. There are no error messages. It won’t pass a tune now. I ran manual tune, changed parameters (em gain, lenses, etc.) and can see that this has an effect. I measured HED volts, 10K. It is intermittent. The ions look poorly formed (pftba), chopped up. I did switch filaments. Any ideas?

Dave

Is PFTBA in the vial ?

I’m working on a 5973. I made some repairs to the gc (6890). I brought everything back up, got a nice tune, and returned to service. The customer was running and half way through, lost signal from the msd. There are no error messages. It won’t pass a tune now. I ran manual tune, changed parameters (em gain, lenses, etc.) and can see that this has an effect. I measured HED volts, 10K. It is intermittent. The ions look poorly formed (pftba), chopped up. I did switch filaments. Any ideas?

Dave

Is PFTBA in the vial ?

Yes

When you say you switched filaments, did you take it apart and put new ones in or did you merely flip the switch in the software to go from one to another? You may have switched from one burned out filament to another.

In my experience, whenever I've lost signal during a seemingly good chromatographic run, the filament burned out.

Check the repeller insulators. Sometimes the EI source heats up, the repellers expand and they end up shattering if the nut is too tight. The newer 5975's have 3 extra concave washers to act as a spring for this reason. My instrument (an older 5975) was breaking them all the time untill I bought the washers.

When you say you switched filaments, did you take it apart and put new ones in or did you merely flip the switch in the software to go from one to another? You may have switched from one burned out filament to another.

In my experience, whenever I've lost signal during a seemingly good chromatographic run, the filament burned out.

Replaced filaments, thank you, pumping down.

Check the repeller insulators. Sometimes the EI source heats up, the repellers expand and they end up shattering if the nut is too tight. The newer 5975's have 3 extra concave washers to act as a spring for this reason. My instrument (an older 5975) was breaking them all the time untill I bought the washers.

Ok, inspected, looks ok, not cracked or shattered, thanks

I’m working on a 5973. I made some repairs to the gc (6890). I brought everything back up, got a nice tune, and returned to service. The customer was running and half way through, lost signal from the msd. There are no error messages. It won’t pass a tune now. I ran manual tune, changed parameters (em gain, lenses, etc.) and can see that this has an effect. I measured HED volts, 10K. It is intermittent. The ions look poorly formed (pftba), chopped up. I did switch filaments. Any ideas?

Dave

Intermittent volts on the HED or intermittent problems with the mass peaks?

Do the peaks look good when doing a Profile scan, or are the tops of the peaks split or "fuzzy" looking?

Sometimes a heavy molecular weight contaminant can collect on the HED since it isn't directly heated. You can remove the two screws holding the insulator on and pull out the electrical connector and remove the HED, then clean the metal button on the inside with IPA on a chemwipe or cotton swab.

Also blow off the entire insides with some canned air including down the insides of the quads, I have had a tiny piece of lint be on the quads and cause problems with tunes.