Air/Water Check differing in atune & etune

Hello everyone,


we have an Intuvo 9000 with a 5977 MSD coupled.

After a colleague changed the septum our etune showed a leak in Air/Water Check. No Problem I thought, I purged the liner, made a succesful leak check and waited for the next day.


The Air and Water check wasn't better. I've checked every connection with a leak detector, fastened every relevant screw, scanned for 69 & 84 while using a coolant spray on every connection - but with no success. The system was in perfect shape.


Then I found in the staple of autotune reports (my colleagues checked every few ours) an "accidential" atune with Wonderful Air/Water Check values and ran an atune myself. I got following results in Air/Water:

etune: H2O 2.6%, N2 23.9%, O2 2.1%

while atune: H2O 0.6%, N2 8.6%, O2 0.8%


I have an idea what the problem is but it doesn't make perfect sense for me. So before I vent the system and create a backlog for our analysis I want to reassure here.


Thanks for your help.

  • Hi d.fischer,

    I am unsure why the differences with the tunes other than to say the tunes are managed very differently in how they work.

    Your numbers do not meet the criteria for a leak. For a true leak , N2 to O2 ratio is approximately a 3 to 1 ratio. When we see high N2 and very low O2, this can be contaminated carrier gas (N2 in the tank with Helium or hydrogen) , or a leak before a gas trap that is pulling air in the line and the trap is removing the O2. 

    Your tunes show a 11 to 1 for etune and 11 to 1 for Atune. The ratios are consistent, just the numbers are different. I would be looking at the gas system as a possible source of contamination.




  • Hi James,


    thank you for your answer. Clearly this was an interesting point.


    We use 6.0 He and I checked every relevant connection of our gas supply. Nothing found. We have a bottle supporting multiple devices (three GC-MS and even four ICP-MS).


    I was wondering, why we had no issues on the other instruments. I had the feeling that there was a contamination in the source that was extracted in the etune while the atune had left the contamination behind. But I had no possibility to vent and take a look. This was now done on Monday.


    I'm pretty ashamed to tell you that this source was the dirtiest I have ever seen in my five years here. I didn't realize our acceleration in sample counts so the Intuvo was also running almost 24/5 like the 7820A/5977B is doing since about two years.


    The Extractor Lens had a nice crust on it and the Repeller was also dirty on it's back side (the side pointing towards the insulator). I was polishing for about four hours and then venting overnight. Now the etune from yesterday and today morning shows nice 3.x% in N2 and 1.0% O2. Phew! Next cleaning date is fixed in three months.


    Thank you kindly for you help.

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