Hi Mike,
try to heat out the GC column of your EA, this helps on our EA with the 
same mass 30 peak problem.

good luck,
Sven

Kubo, Michael D. (ARC-SSX)[SETI INSTITUTE] schrieb:
>
> Hi everyone,
>
> After a long hiatus (several months of down time), I am gearing up to 
> run some EA samples for nitrogen and carbon on our Delta Plus and 
> Carlo Erba 1108 EA and I’m noticing something quite unusual. While 
> idle and with the magnet tuned for nitrogen, the background for mass 
> 30 is around 80 mV, while those for 28 and 29 are approximately 20 mV 
> each. During the run, when introducing the nitrogen reference gas, the 
> trace for masses 28 and 29 shoot up from their background (of course), 
> but what’s unusual is that the mass 30 shoots up as well, but with a 
> significant (~1 second or so) lag to approximately half of the height 
> of the other gases, or about 400-500 mV. When the reference gas “turns 
> off”, the reverse happens, with mass 30 lagging by about a second to 
> SLOWLY return to about 100-120 mV background (it never returns to 80 
> during the run). After my reference gas injections, the mass 30 trace 
> slowly tries to drift back towards baseline, until my nitrogen sample 
> peak elutes, at which point the mass 30 trace rises again to mimic the 
> trace for 28 and 29.
>
> I’m a little confused here. At first I thought it might be a spent 
> reduction (packed copper) reactor, but then I thought I would only see 
> this on my sample peak and not on my reference gas peaks. 
> Alternatively, if there was something magically wrong with my 
> reference gas, I would only see this phenomenon on my reference gas 
> injections and not with my sample peak. Mass 44, 45, and 46 traces for 
> carbon look totally fine.
>
> I will say that I recently had to replace the capillary in my Conflo 
> II interface – the one that runs from the CO2 regulator to the 
> capillary “sniffer”. Could this have anything to do with my problem?
>
> Any and all opinions would be greatly appreciated.
>
> Cheers,
>
> Mike
>
> ****************************************************************************************************************************************
>
> Michael D. Kubo
>
> NASA Ames Research Center
>
> M/S 239-4
>
> Bldg. N239, Room 327
>
> Moffett Field, CA 94035
>
> (650) 604-6110
>

-- 
Sven Steinbrenner

Max Planck Institute for Evolutionary Anthropology
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