LCMS degasser and tuning issue

Hi. I have been working with LCMS since I starting graduate school in 2017. I have enjoyed playing with the instrument and learn a lot through the time staying late at night with the instrument as well as help from Agilent's technical support team. I recently found this great community and forum where I think I can get from those who are experts.

Our lab has an Agilent LC-MS (1260 HPLC and 6120 MSD).

Recently, I noticed bubbles in the solvent tubing after the degasser and high degasser pressure (~1200 mbar; unit on top of my head, but should be lower than 200). We mostly used A,B line so we swapped to C,D line, flush and equilibrated for 2-3 days and degasser pressure dropped. 

It didn't have any issue after that but soon the LC chromatogram shows signs of issues after running samples for a few months.

1) degasser pressure increased (~1200) doesn't drop now even with equilibrating for a while

2) peaks showed weird shapes/splits compared to previous runs, some peaks showed poor reproducibility even running the same standard vial with the same methane and injection volume

3) I thought the tuning might be the problem, so I did checktune, autotune, dual tuning. First the tuning didn't show any peaks so I ran tuning for 2-3 times and it became okay. But after some sample runs, the tuning issue started again. Now the tuning doesn't show any peaks found even after a few tuning rounds.

just to briefly mention what I did so far are:

- cleaned the source, corona needle with mesh and IPA:water 50:50, every day or before every sequence

- checked the nebulizer needle if the tuning mix drops are coming out and also if the spray is coming out 

- changed the column to see any issue with the column 

- changed to a different standard material to see any issue with the sample itself 

- changed the solvent bottles to new solvent mix

- refilled the tuning mix bottle to a new one

- In September, we did the DIY N2 generator annual maintenance. The whole system was shut down during the maintenance and vent down after.

So my questions are:

Q1) high degasser may be due to a leak or crack in the degasser. To be sure where to find the issue (like is it the chamber or the membrane tube), is there a good procedure before purchasing the parts? If so, how difficult is for fixing the degasser and what are important things to keep in mind for DIY troubleshooting.

Q2) What could cause the tuning issue with no peaks found but only noise showing?

I understand it might be hard to say from what I have described but if any other information is needed, I will be happy to reply back. 

Thank you very much!!

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