Analytical Chemistry article:
Combining Denitrifying Bacteria and Laser Spectroscopy for Isotopic Analyses (δ15N, δ18O) of Dissolved Nitrate
Determination of δ15N and δ18O in dissolved nitrate by denitrifying bacteria and laser isotope analyzer
David X. Soto *?, Geoff Koehler?, and Keith A. Hobson?
? Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan, Canada, S7N 3H5
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Abstract
We present a novel approach for nitrogen (δ15N) and oxygen (δ18O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3– by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA- I.) The use of OA-ICOS technology yields accurate and precise δ15N and δ18O results for dissolved nitrate Samples when nonlinearity issues are considered. This new isotope analytical technique thus improves the isotopic analysis of nitrates by (i) provides accurate measurements of δ15N and δ18O without preconcentration, (ii) eliminated interferences by other gas substances (ie, H2O and CO2), And (iii) reducing extensive maintenance and costs of isotope ratio mass spectrometers (IRMS). This approach will greatly streamline the identification and quantification of Nitrate sources in aquatic systems.
Regarding the isotope measurement of nitrate samples δ15N and δ18O in water, we propose an innovative and revolutionary method: using N2O and off-axis integral cavity output spectroscopy technology (abbreviation: OA-ICOS technology) produced by denitrifying bacteria culture transformation. For the measurement of dissolved nitrate samples, the N2O gas sample collected from the headspace was injected into a N2O laser isotope analyzer based on OA-ICOS technology with a syringe. The manual inlet has a diaphragm seal. Sample analysis time: 300 seconds . This OA-ICOS technology provides high precision and high accuracy δ15N and δ18O isotope ratio results.
This new isotope analysis technique has the following advantages over traditional isotope analysis methods:
1. Provide an accurate measurement of the δ15N and δ18O isotope ratios without preconcentration;
2. Eliminate interference from other gases such as water and carbon dioxide;
3. Saves a lot of cost and maintenance costs compared to isotope mass spectrometers.
This method will greatly simplify the identification and quantification of nitrate sources in the water system.
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