Work

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

Year: 2025

Type: article

Abstract: 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.

Source: Rapid Communications in Mass Spectrometry

DOI: 10.1002/rcm.10052

Authors: Xinying Ling, Juske Horita

Institutions: University of California, Riverside, Texas Tech University

Language: English

Topic: Groundwater and Isotope Geochemistry

Subfield: Geochemistry and Petrology

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Clean water and sanitation

Open Access status: bronze

Funder: National Science Foundation