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Knowledge of hydrogen isotopic fractionation (ε) of plant leaf waxes is the foundation for applying hydrogen isotope values (δ 2 H) in environmental reconstructions. In this work, we systematically investigated plant ε values (ε alk/precipitation , ε alk/soil water , ε alk/leaf water and ε alk/lake water , representing the isotopic fractionation between plant n-alkane δ 2 H and precipitation δ 2 H, soil water δ 2 H, leaf water δ 2 H and lake water δ 2 H) from the natural environments and manipulation experiments. The results show that the ε alk/precipitation values of terrestrial plants have large variations (from -190 ‰ to -20 ‰) and become more negative with increasing aridity index. This phenomenon is possibly caused by the δ 2 H changes in source water (from precipitation to soil water and then to leaf water) during plant leaf wax synthesis under various evapotranspiration conditions in different climatic zones. The rainfall manipulation experiments show that leaf water δ 2 H values are generally higher than soil water δ 2 H values, and the latter are higher than precipitation δ 2 H values. This finding further demonstrates that the evapotranspiration effect on source water δ 2 H affects the quantification of the leaf wax apparent ε values (ε alk/leaf water  < ε alk/soil water  < ε alk/precipitation ). The ε alk/lake water values of submerged plants display a smaller range (-153 ± 5 ‰) than the ε alk/precipitation values of terrestrial plants, which is close to the terrestrial ε alk/precipitation values in humid areas. Therefore, the biosynthetic ε value of terrestrial plant leaf waxes is relatively constant (ca. -153 ± 5 ‰), and the observed variable apparent ε alk/precipitation values are possibly caused by the varied degree of evapotranspiration effect on the water that plants used in different climatic conditions. This effect should be considered when applying δ 2 H values of leaf waxes to trace environmental changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The nitrogen and oxygen isotopes of NO 3 - are effectively used to trace the main nitrogen sources and migration processes in the atmosphere, water and soil. NO 3 - can be converted into N 2 O by the bacterial denitrification method, which is an advanced method with high sensitivity. However, due to the existence of a small but inevitable blank during the whole experimental process, the N isotopic signal of N 2 O produced by denitrification superimposes on that of the N blank. Currently, the standard curve correction method is used to correct measured nitrogen isotope results to mitigate blank interference. It has been reported that high variability of the nitrogen isotope results have been produced by the denitrifier method by conducting an interlaboratory comparison of denitrifier methods and other methods on standards and environmental samples, and to reduce this problem, the nitrogen isotope calibration process with a standard curve is examined in depth in this paper, which uses PreCon-GC-IRMS to determine the nitrogen isotopes in N 2 O. We demonstrate for the first time that reliable results can be obtained without correction for samples with nitrogen isotope composition ranging from -9.9 to 19.5‰, which covers the natural sample range. This study establishes the double test approach for the bacterial denitrification method, ensuring the accuracy and long-term stability of different batches of nitrogen isotope results., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Rationale: Gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS) is widely used for compound-specific carbon isotopic analysis. However, current isotopic analysis systems utilize the GC IsoLink combustion reactor, and independent reduction furnaces are not implemented. Therefore, whether this limitation in furnace use affects the precision of compound-specific carbon isotopic analysis needs to be evaluated., Methods: We attempted to add a separate reduction furnace to the GC IsoLink interface and compared the δ 13 C values of n-alkanes (including C and H elements), fatty acid methyl ester (including C, H, and O elements), caffeine (USGS61 and USGS62, including C, H, O, and N elements), and 9-ethylcarbazole (including C, H, and N elements) before and after the addition of the reduction furnace using the GC IsoLink combustion reactor., Results: For n-alkanes and fatty acid methyl esters, the δ 13 C differences between the measured values and their standard values were basically falling within 0.5‰ whether or not an independent reduction furnace was added. However, for the nitrogen-containing compounds (caffeine and 9-ethylcarbazole), the δ 13 C differences between the measured values and their standard values were much larger without an independent reduction furnace (1.0-3.71‰ for USGS61, 1.78-2.19‰ for USGS62, and 0.39-1.13‰ for 9-ethylcarbazole) than with a reduction furnace (-0.31-0.68‰ for USGS61, -0.44-0.06‰ for USGS62, and -0.04-0.25‰ for 9-ethylcarbazole)., Conclusions: The addition of an independent reduction furnace had no significant effect on the δ 13 C of n-alkanes and fatty acid methyl esters, but it had a significant effect on the δ 13 C of nitrogen-containing compounds. It is suggested that GC IsoLink needs an independent reduction furnace to effectively eliminate the interference of NO x on CO 2 isotopic determination to improve the accuracy of δ 13 C for nitrogen-containing compounds., (© 2022 John Wiley & Sons Ltd.)

Nitrate (NO 3 - ) contamination has become a dominant international problem in the aquatic environment, so identifying the sources and transformations of NO 3 - is the basis for improving water quality. Since the Jing River is the largest tributary of the Wei River, to understand its water quality, this study collected surface water samples from the Shaanxi section of the Jing River during the dry season. The potential sources of NO 3 - were analyzed by hydrochemical and bi-isotopic methods, and the SIAR model was used to estimate the proportional contribution of each source. Results indicated that NO 3 - -N was the main form of inorganic nitrogen in this area, and the average total nitrogen content was 10.23 mg·L -1 , which showed that nitrogen pollution was highly serious; the transformation process of nitrogen in this study area was mainly nitrification; The results of Bayesian model showed that manure and sewage contributed to the most NO 3 - (64.39%) in the dry season, followed by soil nitrogen, which was 26.35%. These results help to adopt better nitrogen management measures to meet the national environmental quality standards for surface water., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Rationale: The condition of the pyrolysis reactor is very important for obtaining stable, precise hydrogen isotopic ratios using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC/TC/IRMS). However, few studies of the conditioning process have been conducted, and little is known about the best methods for high-precision hydrogen isotope analysis., Methods: We investigated δ(2)H variations and observed the changes in carbon coating using six different conditioning methods for the pyrolysis alumina tube: (i) no treatment; (ii) conditioning with 4 μL hexane; (iii) conditioning with 2 μL hexane; (iv) conditioning with 2 μL hexane followed by backflushing overnight; (v) conditioning with 10 s of backflushing with methane; (vi) conditioning with 3 s of backflushing with methane., Results: Conditioning the alumina tube can improve the pyrolysis efficiency of organic compounds because a moderate amount of carbon acts as a catalyst in high-temperature regions of the alumina tube. Carbon actually flows in the tube and is difficult to confine to the high-temperature region. Insufficient amounts of carbon in the high-temperature regions lead to incomplete pyrolysis of organic compounds and lower δ(2)H values due to kinetic fractionation of hydrogen isotopes. In contrast, excess hexane or methane can lead to higher δ(2)H values, probably due to enrichment of deuterium in the hydrocarbon residue., Conclusions: The δ(2)H values obtained by Method 6 are closest to the TC/EA δ(2)H values and are more precise than those obtained by other methods, perhaps because this method introduces a moderate, consistent amount of carbon with each sample injection., (Copyright © 2012 John Wiley & Sons, Ltd.)

Rationale: In recent experiments, we found that compound-specific δ(2)H values can vary as a result of changing the gas chromatography temperature program under common pyrolysis conditions. To achieve better precision, it is necessary to examine the details and find a solution to this problem when using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC-TC-IRMS) for hydrogen isotope analysis., Methods: A test was designed to find the possible temperature effect under four different GC temperature ramp rates using n-alkanes (n-C(21), n-C(27), and n-C(31)) and fatty acids (n-C(12), n-C(18), and n-C(24)). The common 'hexane' method was used initially to condition the pyrolysis reactor. Experiments were then carried out using the 'methane condition' method because it was considered to improve pyrolysis efficiency., Results: Under the 'hexane condition' the measured hydrogen isotope ratios of the n-alkanes and n-fatty acids became more positive with increasing GC temperature ramp rate. The ion current intensity of hydrogen also generally increased. However, when the 'methane condition' method was used, the measured δ(2)H values of the n-alkanes and n-fatty acids showed little change under different GC temperature ramp rates., Conclusions: Higher pyrolysis efficiency could reduce the tailing of the H(2) peak and the related isotopic variations at increased GC temperature ramp rates. In addition, too slow a temperature ramp rate could broaden the peak width and thus increase the background effect and possible isotopic fractionations in the split interface; this could also influence the hydrogen isotope values. We therefore suggest that the appropriate temperature ramp rate is an important factor in improving the precision in analyzing compound-specific hydrogen isotopes., (Copyright © 2012 John Wiley & Sons, Ltd.)