Effect of Organic Matter in Water Samples on the Hydrogen Stable Isotope Ratio Determination by Thermal Conversion/Elemental Analysis-Isotope Ratio Mass Spectrometry
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ABSTRACT
BACKGROUNDIn the study of hydrology and water resources, the hydrogen stable isotope ratio (δ2H) of water is an important detection parameter, and its changing patterns can be used to identify and quantify the source of water, and reveal the evolution process and formation mechanism of the water cycle. Therefore, the accuracy of δ2H value is very important, which promotes the development of isotope detection technology. High-temperature combustion pyrolysis-element analysis isotope ratio mass spectrometry is a highly efficient and accurate method for the determination of hydrogen isotopes. It is suitable for the detection of water samples containing organic matter.OBJECTIVESTo explore the influence of organic matter content in water on the hydrogen stable isotope ratio (δ2H) and establish a relationship curve between them. Use the relationship to modify the δ2H value of H2O and trace the organic source in organic polluted water.METHODSThermal conversion/elemental analysis-isotope ratio mass spectrometry (TC/EA-IRMS) was used as the main detection method. Ethanol water samples with different volume ratios (r) were prepared, and the δ2H values of the samples were determined by TC/EA-IRMS. Taking r and δ2H as variables, the curve relationship and equation were established.RESULTSA good linear relationship was established by using the ethanol content and the δ2H value as variable with R2 of 0.9996, indicating that the organic matter in the water sample will linearly change the δ2H value. As the organic matter content increased, the δ2H value measured by the water sample gradually shifted toward the δ2H value of the organic matter. Using this linear relation, the δ2H value of H2O in the sample can be corrected when the volume ratio of the organic matter is known. Taking the ethanol experiment as an example, the relative error between the corrected result and the true value was 1.7%. By correcting, the δ2H value of the water molecules in the water sample can be obtained, which helped to accurately understand the state and regularity of the water cycle. At the same time, the linear relationship can also be used to trace the source of the organic matter. In the ethanol experiment that simulated the traceability of the source ethanol, the relative error was only 0.4%.CONCLUSIONSThe linear relationship between organic matter and δ2H has a good application prospect in organic matter tracing.
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