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

Abstract

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.

Exploring the Potential of Electrospray-Orbitrap for Stable Isotope Analysis Using Nitrate as a Model

“…There are well-established protocols to isolate nitrate as silver salts from diverse sample types, including groundwater and brines. 21,26,37,38 To gain insights into how the ESI method can be used for environmental samples in the absence of interfering anions, we measured several samples with known and highly variable δ 15 N, δ 18 O, and δ 17 O values that were prepared as AgNO 3 .…”

“…The use of ESI-Orbitrap as IRMS hence hinges on its ability to measure isotopes reliably in the face of influences of the sample other than the analyte that is being measured (i.e., matrix effects). There are well-established protocols to isolate nitrate as silver salts from diverse sample types, including groundwater and brines. ,,, To gain insights into how the ESI method can be used for environmental samples in the absence of interfering anions, we measured several samples with known and highly variable δ 15 N, δ 18 O, and δ 17 O values that were prepared as AgNO 3 .…”

Lanthanide Molecular Species Generated Fe3O4@SiO2-TbDPA Nanosphere for the Efficient Determination of Nitrite

“…methods and so on [7][8][9][10][11]. Although these methods have considerable sensitivity and detection limits, most of them require complex equipment and instruments and tedious operational procedures and skills, which lack realistic operability and make it difficult to achieve highly sensitive, selective, qualitative and quantitative detection of NO2 − [12][13][14].…”

“…Because of the toxicity of NO 2 − ions, the accepted maximum contaminant levels (MCL) of NO 2 − ions in drinking water are regulated to be 214.2 μM by the World Health Organization (WHO) and 71.4 μM by the U.S. Environmental Protection Agency (EPA) [ 6 ]. Traditional methods for the detection of NO 2 − are given as spectrophotometry, high-performance liquid chromatography, ion chromatography, gas chromatography, electrophoresis, electrochemical methods and so on [ 7 , 8 , 9 , 10 , 11 ]. Although these methods have considerable sensitivity and detection limits, most of them require complex equipment and instruments and tedious operational procedures and skills, which lack realistic operability and make it difficult to achieve highly sensitive, selective, qualitative and quantitative detection of NO 2 − [ 12 , 13 , 14 ].…”