This is definetely NO; every trace of oxygen still present in your
source region gives rise to this signal. I expect that if you keep
your Mass Spec filled with pue Nitrogen for longer times you will see
a decrease at mass 30, although I doubt that you will reach the
expected value for pure nitrogen.
I had some experience in using mass 30 for work in which we had to
analyse Nitrogen gas dissolved in water; we used mass 30 to see if we
got rid of the dissolved oxygen properly, and it appeared to be
impossible to get the mass 30 really low (higer was very simple,
obviously). When trying with pure 5.0 N2 we still got some signal on
mass 30, as you do.
hope this helps, regards,
>Hello, 12th June 2008
> I'd like to present some data that I obtained yesterday with
>our Varian/Finnigan MAT 250. These values are comparable with data
>from cylinder N2 that we obtained about ten years ago.
>Peak ratios, corrected for backgrounds
>N2 isotopes Liquid N2 boil-off Cylinder N2
>Expected from Natural Abundance
>29/28 7.165 E-3 7.126 E-3
> (0.981 x Nat. Abund.) (0.975 x Nat. Abund.)
>30/28 2.406 E-4 2.532 E-4
> (18.02 x Nat. Abund.) (18.97 x Nat. Abund.)
>30/29 3.358 E-2 3.553 E-2
> (18.38 x Nat. Abund.) (19.45 x Nat. Abund.)
> It looks to me like we have a sizeable contaminant at mass 30.
>At the risk of displaying our ignorance, might others have noticed
>similar, unexpected increases at mass 30 from liquid and cylinder
>nitrogen? We are thinking to use FTMS to resolve what the
>contaminant might be (perhaps nitric oxide?), but as yet have not
>had opportunity to run the FTMS spectrum.
> Thank you, Frank Simpson
>School of Pharmacy
>email: [log in to unmask]