Large artifact peak, no real signal on QToF instrument - WKB51479

SYMPTOMS

• Large artifact Peak at 286 Da in Negative Resolution mode
• Peak is visible in Operate and Source Standby
• All other modes have normal signal
• Low-mass peaks are still visible when zoomed in and have the proper resolution and isotopic pattern

ENVIRONMENT

• SYNAPT G2-Si
• SYNAPT G2-S
• SYNAPT G2
• SYNAPT XS
• Xevo G2-XS QTof
• Xevo G2-S QTof
• Xevo G2 QTof
• Xevo G2-XS Tof
• Xevo G2-S Tof
• Xevo G2 Tof

CAUSE

Veff value in Acquisition Settings was reset to 1000.

FIX or WORKAROUND

1. Copy the Veff value from Negative Sensitivity mode.
2. Fine-tune the Veff value to give the correct mass for leucine enkephalin.

ADDITIONAL INFORMATION

Correct settings:

The m/z of the artifact peak is dependent on the Veff value setting. On the Xevo G2-XS, Veff was set to 1700 and the artifact was 374.5. Set the Veff to whatever settings work in the working mode for the same polarity. 

Veff is a very crude mass setting, uncorrected and real time. As mass tends to drift over time, the nominal mass position can shift outside of the window of detection, +/- 0.1amu, when performing detector setup and lockmass setup. If mass accuracy is failing despite good resolution and signal height, nominal mass should be checked and Veff should be adjusted accordingly. In order to achieve best mass accuracy, the resolution should be optimized and best as possible. Then Veff should be corrected to give the proper position. Then detector setup and mass calibrations should be performed. Tuning the resolution can cause the mass position to shift, so setting the Veff prior to optimizing resolution can cause the mass to shift too far away again.