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- Posts: 68
- Joined: Wed Mar 25, 2020 8:52 am
The question is: is the deviation from target mass resolution 0.75da different for different m/z and can this deviation influence the peak area and ratio between peaks in lc-ms significantly?
From what i understand the signal on a qqq become lower the higher you set the resolution. You filter out more of the ion cloud to get better resolution giving less analyte ions but potentially less noise also, in some matrises this give better s/n but Usually optimum is 0.75 da. To achive this the ms has to find the correct voltage settings for each mass to create the target resolution so i gather that even if the target is 0.75 da it may differ a bit over the mass range. I see that my instrument says 0.6-0.9 is acceptable for calibration to pass for calibration compounds when target is 0.75.
Have I undestood correctly?
If i am correct, then it means that the ratio between compounds of different mass is influenced if the lower mass is at 0.6 da resolution and the higher mass at 0.9 da. When recalibrating this can change so the lower is at 0.9 da resolution and the higher at 0.6. And thus the ratio between the two masses change after calibration.
I do relative quantifications and it is important for me to know what can influence the ratios of analytes of different mass. It would imply not to recalibrate within a study set of samples. And to be cautious when comparing datasets run with different instruments.
I have a problem that a few compounds all around 700m/z have lower signal 20% of the expecte and low noise 20% of normal also. Above 720 m/z it looks normal. Instrument is more or less new so i suspect calibration but not sure. It is not sample matrix or method verified on other instruments, ms scans are clean from large contamination. Any suggestions what could cause signal and noise reduction in a certain mass range only?