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Melissa,

If the samples are enriched with 15N then use the method of: Stevens RJ & Laughlin RJ 1994 Determining N-15 in nitrite or nitrate by producing nitrous oxide. SSSAJ 58:1108-1116.

THis method was based on KCl soil extracts. But it can easily be used with water samples. It first determines the enrichment of the nitrite, then the nitrite is selectively removed using sulphamic acid and the nitrate is converted to nitrite and the nitrate 15N determined is then determined. The method is based on the reaction of hydroxylamine reacting with nitrite to form N2O.

To my knowledge this has not been used for natural abundance samples. But the basis of the method could perhaps be used to remove any nitrite in your samples.

Regards,

Tim Clough

>
>
> Hi All,
>
> We would like to measure the 15N content of NO2 in freshwater
> samples. Currently we can only
> measure combined NOx(by reducing NOx to NH4 with Devardas alloy,
> converting NH4 to NH3
> with MgSO4and trapping the NH3 on acidified GF/D filters). Can this
> method be modified to
> differentiate the NO2 and NO3.
>
> kind regards
>
> Melissa D. Bautista
> IRMS Research Technician
> Centre for Coastal Biogeochemistry
> Southern Cross University
> P.O. Box 157 Military Road
> Lismore NSW 2480
> Phone (02) 66 269 565
> Mobile 0431928278



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Dr Tim Clough,
Soil & Physical Sciences Group,
Agriculture & Life Sciences Division,
Lincoln University,
PO Box 84,
Lincoln 7647,
New Zealand.

Fax (64)(3) 325 3607
Phone (64)(3) 325 3838 extn 8360