Ammonium 15N Guide
Ammonium isotopes are measured by the conversion of aqueous ammonium to nitrite via hypobromite oxidation, followed by conversion of the nitrite to nitrous oxide via the denitrifier method. The product, nitrous oxide, is then measured on an IRMS.
Sample Volume
- The calculator below specifies the quantity of sample needed for a single measurement. We recommend sending enough sample for a minimum of four measurements.
- 20 nmol of the analyte is injected per measurement.
- A sample concentration of at least 10 µM is required to analyze the sample.
- We recommend sending an excess of sample whenever possible.
Notes and Tips
Preservation
- A small quantity of sulfuric acid may be added to bring the sample to ~pH 2-3 and prevent the loss of ammonia (g).
- Since this method requires bacterial conversion, poisoned samples cannot be analyze.
- The nitrous oxide produced for our measurements will include any present nitrite and nitrate. Therefore, our reported values will include both of these compounds.
- Nitrite can be removed for an additional fee.
- We do not remove nitrate. As a result, if nitrate is present, nitrate's δ15N must be measured separately so that the ammonium δ15N value can be calculated.
- Hypobromite oxidation may oxidize DON present in the solution, so high levels of DON will interfere with the measurement.
Relevant Publications
Zhang et al. 2007 - δ15N Ammonium measurement (note: we perform only the hypobromite oxidation described in this paper, not azide reduction)
Zhang et al. 2007 Supplemental Information - Contains note on DON oxidation
Felix et al 2013 - δ15N Ammonium measurement using the denitrifier method
Granger and Sigman 2009 - Nitrite removal
Zhang et al. 2007 Supplemental Information - Contains note on DON oxidation
Felix et al 2013 - δ15N Ammonium measurement using the denitrifier method
Granger and Sigman 2009 - Nitrite removal