Membrane inlet mass spectrometry method (REOX/MIMS) to measure 15N-nitrate in isotope-enrichment experiments
Membrane inlet mass spectrometry method (REOX/MIMS) to measure 15N-nitrate in isotope-enrichment experiments
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DOI：
10.1016/j.ecolind.2021.107639
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发表时间：
2021-03-30
影响因子：
6.9
通讯作者：
Gardner, Wayne S.
中科院分区：
文献类型：
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作者：
Lin, Xianbiao;Lu, Kaijun;Gardner, Wayne S.
使用 N-15 稳定同位素作为示踪剂来量化同位素富集实验中的氮转化率，可以提高对各种生态系统中氮循环的了解。然而，由于传统技术制备样品的不便，在这些实验中测量少量水中的 N-15-硝酸盐 ((NO3-)-N-15) 是一个重大挑战。我们开发了一种“REOX/MIMS”方法，通过将溶解的无机氮转化为 N-2 后，通过同位素富集实验，应用膜入口质谱 (MIMS) 测定少量水中的 (NO3-)-N-15 浓度。硝酸盐（NO3- + NO2-）被锌粉还原为NH4+，然后铵（NH4+）被次溴碘溶液氧化为N-2。通过MIMS 测量所得的N-29(2) 和N-30(2)。这种优化的方案提供了一种灵敏（类似于 0.1 μM）和精确（相对标准偏差 = 0.1-4.37%）的方法来量化各种盐度 (0-35%) 的水样中的 (NO3-)-N-15 浓度 (0.1-500 μM) 和 2 M KCl 溶液，具有出色的校准曲线 (R-2 >= 0.9996，p < 0.0001）。该方法与(NO3-)-N-15同位素富集培养实验相结合，测量不同生态系统中的总硝化作用和总NO3-固定率。它快速、准确且具有成本效益。这种有效方法的未来应用将为科学家、建模者和决策者提供有关输送到众多水生和陆地生态系统或在其中产生的 NO3 的机制、来源、命运和影响的信息。
Using N-15 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 N-15-nitrate ((NO3-)-N-15) 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 (NO3-)-N-15 concentrations in a small volumes of water from isotope-enrichment experiments after converting the dissolved inorganic N to N-2. The nitrates (NO3- + NO2-) were reduced to NH4+ with zinc powder, and the ammonium (NH4+) was then oxidized to N-2 by hypobromite iodine solution. The resulting N-29(2) and N-30(2) were measured via MIMS. This optimized protocol provides a sensitive (similar to 0.1 mu M) and precise (relative standard deviation = 0.1-4.37%) approach to quantify (NO3-)-N-15 concentrations (0.1-500 mu M) in water samples over a wide range of salinities (0-35%) and in 2 M KCl solution with excellent calibration curves (R-2 >= 0.9996, p < 0.0001). The method was combined with (NO3-)-N-15 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.