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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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  • 0

    You might try running your mass range 35-500 mz and drop the threshold to see what the baseline looks like

  • 0 in reply to ron_tackett

    I thought maybe the column was misaligned, so cut at both ends and reinstalled, and changed the gold seal. Also went to change the inlet liner and the glass wool was pushed out of the top again. It hasn't done that since Herb replaced the EPC module. I let it pump down and air and water check passed a couple hours later. Heated up to operating temps over night. Ran atune this morning and it looked worse--repeller maxed, 219 and 502 % abundance decreased. Decided to bake out MSD again for 0.5 hour and atune--repeller better but 219 and 502 worse. Tried switching filaments and the other was worse, so switched back to #1 and retuned--repeller maxed and 219 and 502 are borderline failing (41% and 2.5%, respectively).

     

    Ran a couple no-injections anyways to recheck baseline and it is still dropping at random points in the run.

     

    Could the baseline problem have something to do with oven temperature, pressure, or flow fluctuations? Not sure how to check if the oven and EPC are functioning properly.

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  • 0 in reply to ron_tackett

    I thought maybe the column was misaligned, so cut at both ends and reinstalled, and changed the gold seal. Also went to change the inlet liner and the glass wool was pushed out of the top again. It hasn't done that since Herb replaced the EPC module. I let it pump down and air and water check passed a couple hours later. Heated up to operating temps over night. Ran atune this morning and it looked worse--repeller maxed, 219 and 502 % abundance decreased. Decided to bake out MSD again for 0.5 hour and atune--repeller better but 219 and 502 worse. Tried switching filaments and the other was worse, so switched back to #1 and retuned--repeller maxed and 219 and 502 are borderline failing (41% and 2.5%, respectively).

     

    Ran a couple no-injections anyways to recheck baseline and it is still dropping at random points in the run.

     

    Could the baseline problem have something to do with oven temperature, pressure, or flow fluctuations? Not sure how to check if the oven and EPC are functioning properly.

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