Improved Methods for High Precision Isotope-Ratio Infrared Laser Spectroscopy of Ecohydrological Waters With Organic Contaminants

IF 1.7 3区化学 Q4 BIOCHEMICAL RESEARCH METHODS Rapid Communications in Mass Spectrometry Pub Date : 2025-04-21 DOI:10.1002/rcm.10052

Xinying Ling, Juske Horita

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Abstract

Rationale

Applications of high-precision isotope analysis of ecohydrological water samples such as soil and plant waters with infrared (IR) laser spectrometry have been hampered by spectral interferences of volatile organic compounds.

Methods

In this study, three methods were tested to remove methanol (MeOH) and/or ethanol (EtOH) added to water for δ²H, δ¹⁸O, and ¹⁷O-excess analysis with Picarro L2140-i: microcombustion module (MCM), pre-treatment with solid-phase extraction (SPE), and pre-treatment with simple MeOH/EtOH combustion (SMEC) method.

Results

The Picarro MCM was not able to combust the alcohols of high concentrations. Hydrophilic–lipophilic balanced (HLB) SPE could adsorb MeOH/EtOH at low concentrations (e.g., 0.1% EtOH). However, its adsorption capacity could be readily exhausted, and adsorbed water on the SPE adsorbents co-elutes and mix with a sample water. The SMEC can successfully combust highly concentrated waters (0.5% MeOH and 1% EtOH) at 450–500 °C, but the alcohol combustion and oxygen isotope exchange with added O₂ could significantly increase δ¹⁸O values (up to 6–7‰) and decrease ¹⁷O-excess (up to 110 per meg) in the presence of a catalyst. The combination of post-analysis corrections of Picarro MCM data (δ²H and δ¹⁸O) and pre-treatment with SMEC method (δ²H and ¹⁷O-excess) can reach the accuracy and precision of ≤3 and ≤2 ‰ (δ²H), ≤0.2 and ≤0.3‰ (δ¹⁸O), and ≤20 and ≤47 per meg (¹⁷O-excess), respectively.

Conclusions

A strategy of combining the two methods is proposed for high-precision isotope analysis of organic contaminated samples: post-analysis corrections of Picarro MCM data (δ²H and δ¹⁸O) and pre-treatment with SMEC method (δ²H and ¹⁷O-excess). The improved methods in this study can provide sufficient accuracy and precision for isotope analysis of plant and soil waters, which can contribute to the fields of ecohydrology and agricultural sciences.

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对含有有机污染物的生态水体进行高精度同位素比红外激光光谱分析的改进方法

应用红外激光光谱法对土壤和植物水等生态水文水样进行高精度同位素分析一直受到挥发性有机化合物光谱干扰的阻碍。方法采用Picarro L2140-i对水中添加的甲醇（MeOH）和/或乙醇（EtOH）进行了去除δ2H、δ18O和δ 17o过量分析的三种方法：微燃烧模块（MCM）、固相萃取（SPE）预处理和简单MeOH/EtOH燃烧（SMEC）预处理。结果Picarro MCM不能燃烧高浓度的酒精。亲水-亲脂平衡（HLB） SPE可以吸附低浓度（如0.1%）的MeOH/EtOH。但是，它的吸附能力很容易耗尽，并且吸附的水在SPE吸附剂上共洗脱并与样品水混合。在450 ~ 500℃的条件下，SMEC可以成功地燃烧高浓度水（0.5% MeOH和1% EtOH），但在催化剂的存在下，乙醇燃烧和氧同位素交换可以显著提高δ18O值（高达6 ~ 7‰），降低δ18O过量（高达110 / meg）。Picarro MCM数据的后校正（δ2H和δ18O）与SMEC法预处理（δ2H和17O-excess）相结合，准确度和精密度分别达到≤3‰和≤2‰（δ2H）、≤0.2‰和≤0.3‰（δ18O）、≤20‰和≤47‰（17O-excess）。结论提出了一种将Picarro MCM数据（δ2H和δ18O）事后校正和SMEC预处理（δ2H和17o过量）相结合的有机污染样品高精度同位素分析策略。本研究改进的方法可为植物和土壤水分同位素分析提供足够的准确度和精密度，对生态水文和农业科学等领域具有重要意义。

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来源期刊

Rapid Communications in Mass Spectrometry 化学-分析化学

CiteScore

4.10

自引率

5.00%

发文量

219

审稿时长

2.6 months

期刊介绍： Rapid Communications in Mass Spectrometry is a journal whose aim is the rapid publication of original research results and ideas on all aspects of the science of gas-phase ions; it covers all the associated scientific disciplines. There is no formal limit on paper length ("rapid" is not synonymous with "brief"), but papers should be of a length that is commensurate with the importance and complexity of the results being reported. Contributions may be theoretical or practical in nature; they may deal with methods, techniques and applications, or with the interpretation of results; they may cover any area in science that depends directly on measurements made upon gaseous ions or that is associated with such measurements.