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

Question asked by ablake on Jun 22, 2018
Latest reply on Feb 25, 2019 by 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!