Dear Isotopers,

We are having trouble running NO3 samples for N-15 in a Carlo Erba NC2500
EA attached to a Finnigan MAT Delta Plus.  Finnigan MAT says the problem is
with the complete combustion of NO3 in a stream of He and O2.  They suggest
adding sugar to the NO3 sample to enhance combustion.  This does not make
sense to me in terms of contamination, however we tried this and the sugar
does improve the N-15 value.  The amount of sugar affects the final N-15
value and  all the N-15 values are 2 per mil to 0.8 per mil too light as
compared to 2 per mil to 2.5 per mil too light without the sugar.  We don't
appear to have this problem with NH4 stds, urea or acetanilide.  Does
anyone have experience with NO3 combustions for N-15 in a EA CF-IRMS system?

Bill Showers
Willaim J. Showers
NCSU Stable Isotope Lab
North Carolina State University
Raleigh, NC 27695-8208

(919) 515-7143 Voice
(919) 515-7802 Fax

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