High mass peaks not selected, calibration fails on a QTof - WKB6836

SYMPTOMS

• The calibration misses peaks at the high mass end of the spectrum
• High mass peaks may be flagged with an !
• May not be able to manually assign the peak due to an interference
• Non-calibration peaks observed throughout the spectra 
• In UNIFI, error states that calibration is invalid for use because "confidence interval threshold exceeded"
• The mass spectral resolution and peak shape are good. See IntelliStart fails the calibration on a QTof (Xevo or Synapt) for how to check or improve the mass spectral resolution.
• Sodium formate high mass peaks are not matched  

ENVIRONMENT

• MassLynx 
• UNIFI
• Xevo QTof
• Xevo G2
• Xevo G2-S
• Xevo G2-XS
• Xevo G3
• SYNAPT G2
• SYNAPT G2-S
• SYNAPT G2-Si
• SYNAPT XS

CAUSE

The calibrant either was prepared incorrectly or has gone bad. 

FIX or WORKAROUND

1. Make fresh calibrant (see How to make sodium formate for QTof calibrations).
2. On the Tune page, ensure that capillary voltage is optimized for maximum sensitivity.
3. Restart the calibration and, in the wizard, select "use the tune page option" for the capillary voltage.

ADDITIONAL INFORMATION

Sometimes increasing the cone voltage to 100 V and optimizing capillary voltage, quad settings, collision energy, and RF settings will help sensitivity at high mass.

Ensure that mass position is correct (adjust Veff, as needed) and that detector setup was recently run.

You may also want to clean the cone. See How to clean the cone on a Waters Mass Spectrometer.