Air Leak in GC/MS located at the transfer line, unsure how to proceed

Question

The system we are using is a 6890N GC coupled with a 5975C MSD. After a recent power outage we pumped the system down and discovered a major air leak with Nitrogen being roughly 50% of ion 69 and Oxygen being 13% after waiting 24 hours from the pump down. We scanned from 0-100 with the manual tune and used a flow of Argon gas to test for air leak locations, and found that the usual locations were not showing a leak. We tested: GC/MS interface nut, Vent valve area, MS side plate, foreline pump and hoses, as well as the GC injector and nuts on the GC portion of the system. The only location where we saw Argon in the scan was where a white cord is connected to the MS transfer line (I've attached a picture). No other location around the transfer line or anywhere else in the system is showing a leak. This is a new one for me and I'm unsure what the repair is. Any help would be appreciated. 
 
 Sean Halloran 
 UC Riverside

SeanTHalloran · Accepted Answer

Hello, 
 I figured I'd update this thread with the final conclusion to the problem. As you requested Paul, I placed the post-it notes underneath the transfer line and tested whether the argon gas was being pulled "down" into a leak below the notes or whether it was occurring at the transfer line. When the placing the argon flow above the notes I still saw the leak, but when placing the flow below the notes the leak was not present. I moved the argon flow around the entire machine including the back and very bottom and saw no argon ions in the scan. 
 So, at this point I finally decided to remove the old braze and replace it with a new one. I did this yesterday, and the air leak is completely gone. Placing the argon flow next to the same place on the machine now shows no argon ion, and the high nitrogen and oxygen counts are now also gone. I believe I can now say with a fair amount of confidence that this part can break over time and that it should be brought up as a potential source of air leaks more frequently than it currently is. 
 In any case, the air leak is now gone and this problem is solved. I hope this thread can be useful for others who are seeing the same problem as me.

Air Leak in GC/MS located at the transfer line, unsure how to proceed

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