Chromatography Forum

Hi,
We have a Saturn 2200 ms here. After replacing the electron multiplier the mass calibration doesn't work well. Al the peaks that should be in the calibration compound show up, but at higher masses than they should.
For example the peak at 69 shows up at 74. When the axial modulation is manually set to 12V (should be around 4v), the 69 peak shifts from 74 to 71, but resolution is lost etc.

Does anyone have an idea what is wrong? leaks don't seem to be a problem as ion counts and water/air peaks are ok.
Is it possible that a small misalignment of the parts of the ion trap cause this problem? (we did disassemble and clean the ion trap).
Thanks for the help,
Frank

Hello --

If you performed another FC-43 tune, and it "fixes" all of the mass assignments upon completion, how long will the mass axis remain stable? How long is it taking the 69m/z to increase to 74m/z?

Knowing little about the instrument's history, I would start with initially doing an RF adjustment. Under Manual Control, adjustments, click on RF adjust and turn the screw on the 2200 until the instrument tells you it is within an acceptable range, minimizing the average counts. Then, ensure your FC-43 pressure is set at a reasonable level, also within the manual control adjustments. Increase or decrease as necessary. Ensure your GC hardware is set with the proper configuration (vacuum detector + correct column length). Tune the system with an analytical flow rate between 0.75-1.50mL/min. Are you using helium?

I would definitely keep the axial modulation between 3-5 volts, 12 volts seems too high.

Hopefully with all of these parameters optimal, your system with maintain tune. What temperature are you maintaining your ion trap at?