Nitrate/Nitrite 15N, 18O Guide
Nitrate + nitrite isotopes are measured by the denitrifier method, which consists of the conversion of aqueous nitrate and nitrite to gaseous nitrous oxide by Pseudomonas aureofaciens, followed by analysis of the product N2O on an IRMS to obtain δ15N and δ18O.
Sample Volume
- The calculator below specifies the quantity of sample needed for a single measurement. We recommend sending enough sample for at least four measurements.
- Ideally, 20 nmol of the analyte is injected per measurement, but the measurement is possible down to 5 nmol with reduced precision.
- A sample concentration of at least 1 µM is required to analyze the sample.
- A maximum of 5.5 mL can be injected per meaurement.
- We recommend sending an excess of sample whenever possible.
Notes and Tips
Sample Preservation
Nitrite Removal
Other
- All samples should be filtered in the field or immediately after collection using either 0.45 um or 0.22 um filter. Samples should then be frozen until subsequent isotopic analysis.
- Samples need to be shipped frozen with ice for overnight delivery.
- Base may be added if necessary, but must be neutralized before analysis
- Since the denitrifier method requires bacterial conversion, chemically preserved samples can generally not be analyzed.
Nitrite Removal
- The nitrous oxide produced for our δ15N and δ18O measurements will be generated from both nitrite AND nitrate. Therefore, our reported δ15N and δ18O values will include both of these compounds.
- If you want the isotopic composition of nitrate, you can remove the nitrite yourself (see Granger and Sigman 2009) or we can remove it for an additional fee.
Other
- A non-zero Δ17O will skew δ15N measurements, as the δ15N correction assumes Δ17O = 0. This is a concern for samples with a substantial atmospheric nitrate input.
Relevant Publications
Sigman et al. 2001 - N analysis
Cascsiotti et al. 2002 - O analysis
Granger and Sigman 2009 - Nitrite removal
Cascsiotti et al. 2002 - O analysis
Granger and Sigman 2009 - Nitrite removal