Extraction of ultratrace dissolved gaseous mercury and reactive mercury in natural freshwater for stable isotope analysis,Journal of Analytical Atomic Spectrometry

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Extraction of ultratrace dissolved gaseous mercury and reactive mercury in natural freshwater for stable isotope analysis
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2021-07-28 , DOI: 10.1039/d1ja00212k
Hui Zhang _{1,

2,

3,

4,

5} , Xian Wu _{1,

2,

3,

4,

5} , Qianwen Deng _{1,

2,

3,

4,

5} , Leiming Zhang _{6,

7,

8,

9,

10} , Xuewu Fu _{1,

2,

3,

4,

5} , Xinbin Feng _{1,

2,

3,

4,

5}

Affiliation

Dissolved gaseous mercury (DGM) and reactive mercury (RHg) are important mercury (Hg) forms in natural water bodies. Knowledge of the concentration levels and isotope compositions of DGM and RHg in aquatic ecosystems is of crucial importance for understanding the fate of Hg and Hg cycle. In this study, we developed a method to preconcentrate the ultratrace levels of DGM and RHg in freshwater for stable isotope analysis. In this method, 10 L of amended water (or after addition of acidic SnCl₂) was purged for 2 hours with Hg-free air gas at 4 L min⁻¹, and the Hg(0) product was then collected onto a chlorine-impregnated activated carbon (CLC) trap. This process was repeated for a total of 80 L water for DGM collection or 40 L of water for RHg collection in order to obtain sufficient DGM and RHg amounts for isotope analysis. DGM and RHg collected on CLC traps were then thermally desorbed and further preconcentrated into 40% acid-trapping solutions for stable isotope analysis using cold vapor multicollector-inductively coupled plasma-mass spectrometry (CV-MC-ICPMS). The method was evaluated by laboratory tests using additions of certified Hg(0) and Hg(II) references with known concentrations and isotopic compositions as well as field measurements of duplicate samples. The laboratory tests showed that 98.1 ± 8.1% of DGM (1sd, ranging from 85.1 to 115.9%, n = 14) and 98.7 ± 8.7% of RHg (81.3 to 122%, n = 33) could be extracted from freshwater, and the isotopic compositions of the extracted Hg(0) and Hg(II) agreed well with the injected Hg(0) and Hg(II) references (paired sample T test: p values ≥ 0.20 for all Hg isotope signatures). Based on the results from the laboratory tests, we propose the expanded uncertainty (2sd) of δ²⁰²Hg, Δ¹⁹⁹Hg, and Δ²⁰⁰Hg to be 0.28‰, 0.07‰, and 0.07‰, respectively, for DGM isotope analysis, and 0.25‰, 0.07‰, and 0.07‰, respectively, for RHg isotope analysis. The duplicate field tests showed negligible differences in DGM and RHg isotopic compositions between the paired samples. These results demonstrate that the extraction method can accurately measure DGM and RHg isotopic compositions in freshwater, providing a useful tool for investigating Hg at ultratrace levels in an aquatic environment.

中文翻译：

提取天然淡水中的超痕量溶解气态汞和活性汞用于稳定同位素分析

溶解气态汞 (DGM) 和活性汞 (RHg) 是天然水体中重要的汞 (Hg) 形式。了解水生生态系统中 DGM 和 RHg 的浓度水平和同位素组成对于了解 Hg 和 Hg 循环的归宿至关重要。在本研究中，我们开发了一种方法来预浓缩淡水中超痕量 DGM 和 RHg 以进行稳定同位素分析。在该方法中，使用 4 L min ^{-1 的}无汞空气将10 L 改性水（或添加酸性 SnCl _{2 后}）吹扫 2 小时，然后将 Hg(0) 产物收集到氯浸活性炭 (CLC) 捕集器上。对总共 80 L 水用于 DGM 收集或 40 L 水用于 RHg 收集重复此过程，以获得足够的 DGM 和 RHg 量用于同位素分析。在 CLC 捕集阱上收集的 DGM 和 RHg 然后被热解吸并进一步预浓缩到 40% 的酸捕集溶液中，用于使用冷蒸气多接收器电感耦合等离子体质谱 (CV-MC-ICPMS) 进行稳定同位素分析。该方法是通过实验室测试评估的，使用添加了已知浓度和同位素组成的经认证的 Hg(0) 和 Hg( II ) 参考以及重复样品的现场测量。实验室测试表明，98.1 ± 8.1% 的 DGM（1sd，范围从 85.1 到 115.9%，n = 14) 和 98.7 ± 8.7% 的 RHg（81.3 到 122%，n = 33）可以从淡水中提取，并且提取的 Hg(0) 和 Hg( II )的同位素组成与注入的 Hg( 0) 和 Hg( II ) 参考（配对样本T检验：所有 Hg 同位素特征的p值 ≥ 0.20）。根据实验室测试结果，我们提出了δ ²⁰² Hg、Δ ¹⁹⁹ Hg 和Δ ²⁰⁰的扩展不确定度 (2sd)DGM同位素分析Hg分别为0.28‰、0.07‰和0.07‰，RHg同位素分析分别为0.25‰、0.07‰和0.07‰。重复的现场测试显示配对样品之间 DGM 和 RHg 同位素组成的差异可以忽略不计。这些结果表明，该提取方法可以准确测量淡水中的 DGM 和 RHg 同位素组成，为研究水生环境中超痕量水平的 Hg 提供了有用的工具。

更新日期：2021-08-12

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