Chromatography Forum

We have a Thermo Velos Pro LTQ (not with an orbitrap), we just got it back up and running but have been unable to get it calibrated correctly. The issue we are running into is that the calibration mass at m/z 138 will not pass because it keeps showing up at m/z 139. All other m/z, both lower and higher than 138, pass without a problem. One thing to note is that m/z 138 is created by in-source fragmentation of caffeine at m/z 195. Any suggestions would be greatly appreciated.

If you infuse solvent with no calibrant, do you see the mysterious 139? (i.e. is it a contaminant that's got nothing to do with the calibration solution)
If you infuse caffeine, and do in-trap fragmentation on it, do you see 138 or 139? (i.e. is it something where it's got really badly calibrated and it's actually mis-measuring the fragment, or is it that something weird is going on in the spray chamber).
It's a long time since I've used one of these instruments, so I can't remember if it's possible to go back to an old calibration and look at what happens there?

We have a Thermo Velos Pro LTQ (not with an orbitrap), we just got it back up and running but have been unable to get it calibrated correctly. The issue we are running into is that the calibration mass at m/z 138 will not pass because it keeps showing up at m/z 139. All other m/z, both lower and higher than 138, pass without a problem. One thing to note is that m/z 138 is created by in-source fragmentation of caffeine at m/z 195. Any suggestions would be greatly appreciated.

Is it possible to do a course calibration on your own? Our Finnigan LTQ, while older, allows us to do that.