Triple oxygen isotope analysis of nitrate using isotope exchange cavity ringdown laser spectroscopy

Gázquez, Fernando; Claire, Mark

doi:10.1002/rcm.8268

Cited by 7 publications

(2 citation statements)

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“…Here we further eliminate the possibility of oxygen isotopic exchange between nitrate and water in acid solution during the extraction process by estimating the δ 18 O value of the isotopically normal end‐member (Δ 17 O = 0‰). If oxygen isotopic exchange between nitrate and water occurred, an x axis intercept (Δ 17 O = 0‰) in the δ 18 O‐Δ 17 O scatter plot (Figure 5) should be close to the δ 18 O value of H 2 O used in this study (approximately –14‰), as shown in a H 2 O‐NO 3 − isotopic equilibrium experiment (Gazquez & Claire, 2018). The actual x axis intercept of 19‰ (Figure 5) suggests that the low Δ 17 O values observed in our study are not analytical artifacts.…”

Section: Resultssupporting

confidence: 68%

A Complete Isotope (δ¹⁵N, δ¹⁸O, Δ¹⁷O) Investigation of Atmospherically Deposited Nitrate in Glacial‐Hydrologic Systems Across the Third Pole Region

et al. 2020

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The Himalayas and Tibetan Plateau, identified as the Third Pole (TP), is a unique region because of its insertion into global environmental and climatic changes. Deposition of atmospheric nitrate in this region is one of the most important sources of reactive nitrogen to glacial-hydrologic system and ecosystems. The isotopic composition of atmospherically deposited nitrate preserved in ice bodies plays a central role in delineating environmental and climatic changes, present, and past. Here, we provide an overview of the complete isotopic compositions (δ 15 N, δ 18 O, and Δ 17 O) of nitrate in aerosol, snow, ice, and water samples (n = 46) collected across the Southern, Southeastern, Central, and Northern TP to constrain complex nitrogen cycles of the atmosphere, cryosphere, hydrosphere, and, potentially, the biosphere. A large variability of snow nitrate isotopic compositions is observed across the TP at different spatial scales (from a single glacier to the entire plateau), likely due to the complex landscape and relevant physical and chemical processes across the TP. Large nitrate Δ 17 O values are observed in water samples collected from the Mt. Everest region, highlighting the considerable fraction (up to 45%) of atmospheric nitrate to the nitrate load in this Himalayan hydrologic system. Our work reveals the complex chemical, depositional, and postdepositional processes over the TP that are greater than previously thought and identifies further comprehensive investigations, which entail using nitrate isotopic compositions as an identifier for nitrate source apportionment in various ecosystems and understanding past atmospheric and climatic conditions in this region. The Himalayas and Tibetan Plateau hosts the largest number of glaciers (>36,000) on the planet outside of polar regions with thousands of lakes and is referred to as the Third Pole (TP) (Yao et al., 2012). This massive water reservoir within this pristine region sustains the water supply and food security for billions of people in ©2020. American Geophysical Union. All Rights Reserved.

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Section: Resultssupporting

confidence: 68%

A Complete Isotope (δ¹⁵N, δ¹⁸O, Δ¹⁷O) Investigation of Atmospherically Deposited Nitrate in Glacial‐Hydrologic Systems Across the Third Pole Region

et al. 2020

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“…In addition to the demonstrated advantages, (1) the method has the potential to be adapted to δ 17 O analysis by online converting the oxygen in the benzyl nitrate to O 2 in a Au furnace, followed by IRMS analysis or to H 2 O after online isotopic equilibrium with NO 3 – , followed by CRDS analysis, , (2) the strategy to convert oxyanions to organic esters can also be easily extended to other oxyanions in natural samples, making the highly desirable simultaneous analysis of oxyanions as a mixture, a possibility, (3) the method is amenable to automation, (4) benzyl nitrate (and nitrite) can be analyzed for δ 15 N analysis on EA/Py/IRMS or GC/Py/GC/IRMS without any further workup, which compares favorably with a recent method where nitrate was converted to nitrobenzene for δ 15 N isotope analysis by GC/C/IRMS (note that 1/3 of the O in nitrate is lost during the conversion to nitrobenzene), and , (5) nitrite can also be derivatized with a similar conversion rate to that of nitrate under the same reaction conditions, with no observed mutual interferences between the two or interference from other coexisting ions (see Figure ). For simultaneous isotopic analysis of both nitrate and nitrite, the advantages of our method are clear as the problems of selective reduction of nitrate or conversions of nitrite to nitrate before bacterial reduction are avoided. , In the next paper of this series, we will report our results on realizing the above-listed potentials, in particular, (4) and (5).…”

Section: Discussionmentioning

confidence: 99%

Novel GC/Py/GC/IRMS-Based Method for Isotope Measurements of Nitrate and Nitrite. I: Converting Nitrate to Benzyl Nitrate for δ¹⁸O Analysis

et al. 2020

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The 18O/16O (and 15N/14N) ratio of natural nitrate (NO3 –) and nitrite (NO2 –) can be used to extract valuable information about their source and fate as environmental contaminants, their metabolism as macronutrients in plants and animals, and their behavior in the N biogeochemical cycle. We developed an accurate, precise, sensitive (minimum sample size: 0.2 μg NO3 –-equivalent), and reliable (minimal oxygen exchange, loss, or gain) method to selectively isolate and purify nitrate and nitrite from natural water, soil, air, and plant materials by strong anion exchange (SAX) for low- to normal-salinity samples or strong cation exchange (SCX) for high-salinity samples, followed by quantitative conversion to their respective benzyl esters, which can be separated and individually analyzed for δ18O (and potentially δ15N) by gas chromatography (GC)/pyrolysis/GC/isotope-ratio mass spectrometry (IRMS). The method compares favorably with the currently popular bacterial denitrification and chemical reduction methods, in terms of sensitivity and reliability, and has the potential to simultaneously measure δ15N and δ18O of nitrate and nitrite from natural samples of various origins.

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