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- Posts: 165
- Joined: Sun Oct 04, 2009 6:18 pm
I'm running a 5973 with a 6890 for air sample analysis. I'm trying to locate the source of some seemingly common contaminants, but I'm struggling to isolate the problem. The system has a concentrator using nitrogen cryo, and I have since removed this from the system, so I just have a 60m Rxi-1 installed directly to the inlet and the MSD.
Originally the issue was high 28 and 32 which I assumed was just an air leak, however when changing parameters, oven, flow, split, splitless, not only do the raw abundances change, but the ratios change as well, and it no longer appears to be air. 28:32 ratio varies between 1.4 and 2.6, and is never consistent. When temps and flows are stable, I can get from <10% 28:69 to over 100%.
Also very strange, is when increasing oven temp to 300 (below the max isothermal of 330) and scanning with PFTBA open, I get 207 to become base, with 281 right behind. 207 jumps around as well, from nearly 200% of 69, to <20%. I see negligible 149 suggesting rubber/plastic isn't the issue.
I've already replaced the nearly two year old column with a fresh one, and still no change. I've capped the MSD and proven it's working ok, with negligible 207, 281, 28, 32.
System does not yet have gas traps installed, however the gas source splits between two systems, and the other system shows no issues.
I'm questioning the source of the ions 207 and 281 in particular. I'm about ready to strip out all the helium lines thinking there's something sitting in the tubing contaminating the system. Any ideas would be appreciated.
Christian