5975c bad tune

[Maxim09]

I work with GC 7890A coupled with 5975c MSD and some time ago (few weeks) it started to show bad performance. All tunes either stunes or autotunes revealed high Emvolts = 3000 plus lots of water (didn't below 30%) and nitrogen (roughly same percentage) and oxygen (roughly 23%). In addition to these issues background upon running samples turned curved from around C20 -C22 and finally last remaining filament died. I vented MSD, shut it down, replaced both filaments, electron multiplier horn and cleaned ion source with alumina slurry. After assembling all analyzer and pumping it down I started almost immediately to see incredibly high background plus a lot extra peaks upon making auto tune.

Can anybody shed a light on what's going on?
I really appreciate any help and suggestions

[Steve Reimer]

Assuming you still have pftba and the valve is opening during tune, it sounds like your system can't find enough 69 ion to reach a tune. When you run atune what do the plots look like? Just noise or do they look like they are not maximizing. Also, can it find the right peaks? It may be necessary to load an old tune file if you have saved one of the bad ones. Something clearly is not working and it may take a service rep to find what it is.

[kubowicz.tomasz]

Hello

Please paste autotune report.
First of all it looks like massive leak - what is the nitrogen/oxygen/water level after ion source cleaning?

Regards

Tomasz Kubowicz

[Maxim09]

Hi Steve and Tomasz
Thanks a lot for your responses. Here is the link so you can take a look on autotune:

https://drive.google.com/open?id=0B56qo ... QxOEZRTUM0

I guess auto tune plots are more or less ok. The last one, 502 looks a bit ugly. It find peaks all right. It has enormous amount of everything, H2O, N2, O2 and CO2. But I didn't do thorough conditioning of a column or baking an analyzer

[kubowicz.tomasz]

Hello

I've checked autotune report. First of all:
There is massive leak!! Look at water/air. Also vaccum level is not displayed properly (it happens sometimes with MSD Chemstation) or there is no vacuum at all.
Please check your system for leaks. It is very first step.

Regards

Tomasz Kubowicz

[Maxim09]

Thank you Tomasz for good suggestion. I want to start with outside fitting, but i do have only liquid leak detector. Agilent says it's better not to use it. Do you have any suggestions how to check without electronic detector?
Thanks

[Steve Reimer]

Check with "Dust Off" or other aerosol dust remover containing a fluorocarbon. In manual tune scan for 69 or other ion, depending on the fluorocarbon. Turn off the ptfb and start spraying likely parts. Side door seals are a good place to start. When the spray finds the leak the counts will go from a few hundred to 100s of thousands for a bad leak.

[James_Ball]

It would also be good to cap off the inlet with a no hole ferrule. If the leak goes away then it is somewhere in the column, inlet or GC plumbing. If it stays, then your leak is in the analyzer itself.

Vacuum reading may no be there if the ion gauge option was not installed.

Are you certain there is good clean helium going into the GC and also look closely at the column to make sure that it hasn't broken somewhere in the middle. I have had that happen before and not notice the broken column at first.

[Maxim09]

It turned out to be a leak in detector (column is removed). I lubricated side-plate o-ring and vent valve with grease, checked them as well as GC/MSD (capped) interface. All of them didn't show a leak with argon balloon. But overall leak remains in a system an it increases with time!

[James_Ball]

It turned out to be a leak in detector (column is removed). I lubricated side-plate o-ring and vent valve with grease, checked them as well as GC/MSD (capped) interface. All of them didn't show a leak with argon balloon. But overall leak remains in a system an it increases with time!

Try tightening the four screws on each end of the analyzer, they hold the end caps on and there is a seal under them I think. Also can have a leak at the ion gauge fitting or where the calibration gas valve attaches. Another place these can leak is where the transfer line heater attaches to the side of the analyzer. We also had one that the inlet cracked right behind the threads where the column interface nut attaches, the interface finally broke right behind the threads is how we found that leak.

[mdevay]

also check the vent valve o-ring