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

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

results from changing mass range and threshold. Also looked at ions in normal baseline vs dropped baseline and it seems like everything stays in proportion, just drops abundance.

results from changing mass range and threshold. Also looked at ions in normal baseline vs dropped baseline and it seems like everything stays in proportion, just drops abundance.

Probably not helpful, but your background is relatively normal except that the 44 peak from CO2 is very high. Argon (40) is present in air at ~1% and C02 should be at ~400ppm (0.04%) a ratio of 25:1  Your ratios vary between ~14:1 and 7:1 the “wrong” way. The 207 siloxane peak only varies by <50% and the 281 siloxane peak seems to vary even less  - The CO2 may be adsorbed on an active surface between runs and desorbed as the system gets hot, so possible places are the injector/liner or injector trap filter. A stupid thought - You don’t have an instrument with liquid CO2 sub-ambient cooling, or another source of CO2 in the lab?

Thanks for the suggestion. It's unfortunate I can't find a scan to compare the CO2 and Argon to, because we usually scan only from 50-550 m/z. I have the injector off and replaced the inlet liner, but will check out the split vent trap. And no sources of CO2 in the lab.