Why Agilent 6520A QTOF instrument ms/ms off by 2 Dalton? MS1 is accurate.

Hi zhenfazhang ,

When did you last perform an initial tune or system tune on both the Quad and TOF? 

Are you seeing the same thing in positive and negative polarity?

It should not cause this issue, but please also verify that the nitrogen 99.999% cylinder is not empty.

Hi zhenfazhang ,

When did you last perform an initial tune or system tune on both the Quad and TOF? 

Are you seeing the same thing in positive and negative polarity?

It should not cause this issue, but please also verify that the nitrogen 99.999% cylinder is not empty.