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GCMS drops in baseline with recovery during no-injection post maintenance

ablake

System specs:

Agilent 6890N with 5975 iMSD and MassHunter GCMS Acquisition/ Enhanced Chemstation Data Analysis

Split liner, helium carrier gas, flow=3ml/min during bake outs and 1mL/min all other time

 

The vacuum system failed over a weekend and was replaced with a refurbished unit. Pumped down and sat for a week at ambient temps. Then we changed the column (DB-1MS max temp 340'C) and septum as part of regular system maintenance. Air and water check passed with source and quad at 80'C. Baked column at 325'C attached to source for 2.5 hours. Checked condition of column (see attached document), then baked out MSD and ran a few no-injections with needle off. These are in full scan (50-550 mz) and look great minus the drops in baseline, which I have never seen before. Autotune looks good as well. Has anyone else ever seen this before? I don't know if you could call them negative peaks.

 

Any suggestions or comments would be greatly appreciated!

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    Hi ,

    we had the same problem in our lab. In our case, the baseline was randomly jumping up or down for a random amount of time and in a totally irreproducible way. So we cleaned the source, swapped the source, installed a new multiplier, cleaned the HED, cleaned the quadrupol, switched out the HED power supply cable, the electronic board on the side of the analyzer door, the complete analyzer, the electronics under the analyzer...

    The problem seemed to have been gone after a few of these steps, but returned a few days later. Finally, we switched the foreline vacuum pump. Success! The vacuum had been inconsistent, possibly because of a leak somewhere in the foreline pump. The baseline has been stable since then. So, if your baseline starts jumping again, you might want to check or replace the foreline pump.

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