Membrane inlet mass spectrometry method (REOX/MIMS) to measure 15N-nitrate in isotope-enrichment experiments
Using 15N stable isotope as a tracer to quantify N transformation rates in isotope-enrichment experiments improves understanding of the N cycle in various ecosystems. However, measuring 15N-nitrate (15NO3−) in small volumes of water for these experiments is a major challenge due to the inconvenience...
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| Autores principales: | , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Elsevier
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/b563f395770146ff884966fb2f5cc8e0 |
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| Sumario: | Using 15N stable isotope as a tracer to quantify N transformation rates in isotope-enrichment experiments improves understanding of the N cycle in various ecosystems. However, measuring 15N-nitrate (15NO3−) in small volumes of water for these experiments is a major challenge due to the inconvenience of preparing samples by traditional techniques. We developed a “REOX/MIMS” method by applying membrane inlet mass spectrometry (MIMS) to determining 15NO3− concentrations in a small volumes of water from isotope-enrichment experiments after converting the dissolved inorganic N to N2. The nitrates (NO3− + NO2−) were reduced to NH4+ with zinc powder, and the ammonium (NH4+) was then oxidized to N2 by hypobromite iodine solution. The resulting 29N2 and 30N2 were measured via MIMS. This optimized protocol provides a sensitive (~0.1 μM) and precise (relative standard deviation = 0.1–4.37%) approach to quantify 15NO3− concentrations (0.1–500 µM) in water samples over a wide range of salinities (0–35‰) and in 2 M KCl solution with excellent calibration curves (R2 ≥ 0.9996, p < 0.0001). The method was combined with 15NO3− isotope-enrichment incubation experiments to measure gross nitrification and gross NO3− immobilization rates in various ecosystems. It was rapid, accurate, and cost-effective. Future applications of this efficient approach will inform scientists, modelers and decision makers about mechanisms, sources, fates, and effects of NO3− delivered to or produced in numerous aquatic and terrestrial ecosystems. |
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