mass shift

[smkh]

Hi everyone
I have aproblem when I do tuning at API5000, the instrument is calibrated recently with alogic result of the intensity , width and mass shift , when I do Q1-Scan or product ion (MS2)-Scan, i get the dominant peak +/- my intrest peak , for example if I'm seeking to get (Q1-Q3)(218-116) i get (217.2-119) or if iwant(417.5-234.5) i get (416.8-235. and many more similar examples , is it possibe for me to work in this shift even if it not matching the literatures
what cause this problem and how can i solve it please?!

[sassman]

Either your instrument was not calibrated properly or you are not using the correct mass for your compound. Make sure that you are using the monoisotopic mass of your compound (not average mass). There is a handy molecular weight calculator here: http://ncrr.pnl.gov/software/ (at the bottom of the page). Please tell us what instrument you are using and what compounds you would like to analyze. If you used an automatic calibration method, perhaps you should try to calibrate the instrument manually. On our API3000 using PPG solution to calibrate, the automatic method sometimes picks the wrong mass for some of the calibration points (especially the higher masses where the most abundant mass is not the right one).

[Steph5217]

API 5000 has a very stable calibration. Resolution is 1.

It's rare the calibration moves. Think about a very bad calibration.

[yangz00g]

You must either have a wrongful calibration, or bad data-acqusition settings/software issue. I haven't tuned my 5000 for over four months, the mass accurcy (+/-0.5 amu) is still good.

[smkh]

Hello everyone;
Thanks very much about all replies
finally the problem is solved by readjust the calibration settings ,although the calibration is done three times and in all these times it gives agood results!!!
the problem occured at the low masses between 200-500 as a result of the investigation which cause abig trouble for me because all of my work cocern this range!! but now it works well.