The ESI-MS attached to our analytical HPLC is a Thermo MSQplus model. The mass scale was off by couple of units (+2 m/z) for a long time. I have recently started working with it and because I need analytical LCMS data, I decided to re-calibrate and re-tune the MS. According to Thermo manual, the calibration solution is NaI/KI/CsI mixture in 1:1 IPA and water. However, every time I try to recalibrate it, I get an error saying "Calibration standard deviation too large" and "Calibration residuals too large".
I have made multiple attempts, changed solvents, made new calibration solution, filtered it to make sure there are no bubbles etc etc but nothing changed. Worse, I can see the m/z scale is drifting even more with every attempt to calibrate it.
When I inject the calibration solution into the MS, I can see the appropriate peaks (esp at lower m/z) but I do notice that the resolution is really bad and the peaks are flat at top instead of being pointy.
Any suggestion to help calibrate/diagnose would be really appreciated.
Sounds like the instrument needs maintainence or repair. No reason to try to calibrate a broken instrument
Check the log book. When was the instrument last cleaned or successfully tuned. Have the settings changed since then? If these settings are problematic as well you can try the factory settings.
But first before fiddling with the settings I have to say that flat topped peaks sound like the calibration solution may be way too concentrated - check you have these right and that the flow rate of calibrant is not too fast. These are sensitive instrument - less is more.
Check to see if you can load the default or factory calibration, if so you can then proceed to the cesium iodide clusters.
Hi everyone, Thanks a lot for your answers... Scot and Vinod were right, I have given up on the instrument now. It is beyond me to fix it :(
Charles, I have made and remade the calibration solution and the concentration of each ion is as instructed by the manual. However, you are right about the previous cleaning and tuning of the instrument. I cant find the last time it was properly cleaned or tuned. I am not talking about cleaning the ESI injector (that is cleaned pretty frequently) but the quadrupole seems to have never been cleaned in last 4 years. The instrument was mistuned a long time too before I decided to try it.
As suggested by Charles and Jeffery, I wanted to try and load the factory settings but A.) I could not find it easily (nothing in manual about it). B.) My boss wants me to not spend any more time on it (probably right)
After detailed phone discussion with a tech from Thermo, the problem seems to be that the RF voltage is off by some amount from what it should be and only a service engg can fix it.
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