- RMS error and mass difference results look great (0.3 ppm and 0.3 mDa).
- Confidence interval was 250.
- Xevo QTof
One of the calibration points had picked the incorrect, more intense ion.
FIX or WORKAROUND
- Find the mass or masses that have a much larger mass difference than the typical mass difference for the other ions.
- Zoom in and find that it had picked the incorrect, more intense ion.
- Select the reference ion by right-clicking it, and then select the correct experimental ion. It should now be highlighted in red (and not blue).
- Once all of the masses are corrected, select the Create Calibration button and see that the confidence interval is much smaller now and you can save the calibration.