That's NO making it through the reduction column. The GC column is
partially separating it from the N2 peak, and it's main mass is mass
30--which is falling into the most sensitive cup, so you'll see a big
signal before it really starts messing with 15N signal. You'll see that
grown in during a run when the reduction column is on it's last legs.
Double check the temperature on the reduction oven and flow rates. If
they're ok, then you'll probably need to re-pack the reduction column.
On 6/18/2011 9:07 AM, Francesca wrote:
> Hi all,
> can anyone tell me what is that weird mass 30 peak? (you can see it in the
> picture here http://dl.dropbox.com/u/3191726/weird%20mass%2030%20peak).
> Some useful information:
> - we have a Thermo Flash 2000 EA plugged to a Delta V Advantage IRMS
> - last week we run some liquid samples for 15N (samples were enriched up to
> roughly 3permil) using a Thermo AI/AS3000 autosampler.
> - yesterday we switched back to the solid autosampler AS200 (the run you
> see in the picture is a solid acetalinide standard)
> - yesterday we also changed combustion, reduction ovens and water trap
> - d15N of our standards (urea and acetalinide for the moment) are perfect.
> Thanks for your help