Chromatography Forum

I have a 5973 MS which for some reason won't hold tune. More specifically, it keep shifting mass assignments especially at the higher end. Each time I run a quicktune, BFB tune, or autotune I can literally watch mass 502 slowly shift with each passing minute. Mass 502 will become 504 in a day. The mass gain has changed from the usual of about 200 to -1100 over the course of several re-tunings. Everything else seems to be fairly steady. Didn't see anything visually different about the quad. Swapped the main board with no change. Room temperature is very stable. Instrument was given plenty of time to stabilize. DC Polarity hasn't been changed. It had been running fine for a long time. Any ideas?


Ron

You can check on a few things to find the source of the problem:

1) air and water check. If you have a leak, it can cause mass shift.
2) see if ion source is dirty
3) do you have enough PFTBA in the vial?
4) Is electron multiplier voltage too high?(which could mean you need a new one)

I guess I forgot to mention a few more things. It has been doing this both before and after a thorough source clean. The air/water is no more than 2%. The EMV is running at around 2200. There is plenty of PFTBA.

If everything else other than mass gain looks normal, it probably means a harware problem. It could be the quad, the electronics or the ion source (you probably can rule it out because you already cleaned the ion source). Give Agilent a call and see what they say.

A few more things to check: Do you have m/z 414, m/z 464 and m/z 614 mass shift? Do you have a contant mass offset in the tune file? Try 2nd filament and try to change DC polarity. Also, does m/z 502 have a decent abundence? What's the ratio of m/z 502 to m/z 69?

Thanks for the help. Unfortunately, the problem has gotten a bit worse. The shift occurs across the board but much more at the higher end. I've tried both filaments and both polarities. 502 has an OK abundance and a ratio of about 2.5% of 69. The past few days its been holding steady, but as soon as I try running any samples, the masses flip out. I'm using 5973/6890/tekmar 3100/archon autosampler. I've just swapped sideplate boards and will wait until tomorrow to see how it looks.

Sideplate board didn't work. I guess I'll just call someone in.

How did this end?
A good learning point for other users.

My experience, once a thinny piece of carbon, from ferrule was in the ms chamber. This also gave a lot of "nice" shifts.

Okkie

It hasn't ended. Had someone come out to look at the problem. Swapped analyzer and electronics module with no luck. Swapped power supply for turbo. This worked for a few days then the problem came back. I swapped the turbopump itself and this seemed to work for about a week. Now the problem is back. Tried swapping the EPC in case the flow calibration is out of whack but no luck. Will attempt to look for major flow leaks and double check the inner workings of the forepump.