Any chance that you city air has HNO3 from automobile exhaust? Or maybe
other industrial sources?  In North America we are not surprised with
your result.

Peter Vervloedt wrote:
>
> Hello all,
>
> In our laboratory we are measuring 15N in N2O for a short while
> now. We use PDZ Europa's ANCA-TGII. The analysis itself works
> fine ('nice' peaks, low background scans, etc...), but apparently
> we're having some problems with our reference material. We use
> 'the cadmium' technique to produce N2O from KNO3. We assume
> that the %15N in the initial NO3- and in the produced N2O are the
> same. So, we use the measured 15N% value for KNO3 as our
> reference value for N2O. The exact value we became is 0.3630%
> 15N (measured 3x in 5 replicates with the ANCA-SL).
>
> Recently we measured 15N content in N2O in air (outside, in a
> city), using the N2O produced from the KNO3 as described above)
> and we had a result of 0.39-0.40%, which is (probably) impossible.
> The concentration of the reference was the same as the
> atmospheric concentration.
>
> Has anyone had the same experience? I would appreciate it very
> much if someone could help us on this.
>
> Yours,
>
> Peter.
> -----------------------------------------
> Peter Vervloedt
> Ghent University
> Laboratory of Applied Physical Chemistry
> Coupure Links, 653
> 9000 Gent
> tel.: +32 9 264 60 00
> fax.: +32 9 264 62 30
> e-mail: [log in to unmask]
> ----------------------------------------

--
Irene Ellis
Mass Spectrometry Lab
U.S.D.A. Human Nutrition Research Center at Tufts University
711 Washington St.
Boston, MA  02111

(617)556-3007