Global Institute for Water Security, School of Environment and Sustainability, University of Saskatchewan, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada.
NHRC Stable Isotope Laboratory, Environment and Climate Change Canada, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada.
Rapid Commun Mass Spectrom. 2021 Aug 15;35(15):e9118. doi: 10.1002/rcm.9118.
Hydrogen and oxygen stable isotope ratios (δ H, δ O, and δ O values) are commonly used tracers of water. These ratios can be measured by isotope ratio infrared spectroscopy (IRIS). However, IRIS approaches are prone to errors induced by organic compounds present in plant, soil, and natural water samples. A novel approach using O-excess values has shown promise for flagging spectrally contaminated plant samples during IRIS analysis. A systematic assessment of this flagging system is needed to prove it useful.
Errors induced by methanol and ethanol water mixtures on measured IRIS and isotope ratio mass spectrometry (IRMS) results were evaluated. For IRIS analyses both liquid- and vapour-mode (via direct vapour equilibration) methods are used. The δ H, δ O, and δ O values were measured and compared with known reference values to determine the errors induced by methanol and ethanol contamination. In addition, the O-excess contamination detection approach was tested. This is a post-processing detection tool for both liquid and vapour IRIS triple-isotope analyses, utilizing calculated O-excess values to flag contaminated samples.
Organic contamination induced significant errors in IRIS results, not seen in IRMS results. Methanol caused larger errors than ethanol. Results from vapour-IRIS analyses had larger errors than those from liquid-IRIS analyses. The O-excess approach identified methanol driven error in liquid- and vapour-mode IRIS samples at levels where isotope results became unacceptably erroneous. For ethanol contaminated samples, a mix of erroneous and correct flagging occurred with the O-excess method. Our results indicate that methanol is the more problematic contaminant for data corruption. The O-excess method was therefore useful for data quality control.
Organic contamination caused significant errors in IRIS stable isotope results. These errors were larger during vapour analyses than during liquid IRIS analyses, and larger for methanol than ethanol contamination. The O-excess method is highly sensitive for detecting narrowband (methanol) contamination error in vapour and liquid analysis modes in IRIS.
氢和氧稳定同位素比值（δH、δO 和 δO 值）通常被用作水的示踪剂。这些比值可以通过同位素比红外光谱（IRIS）来测量。然而，IRIS 方法容易受到植物、土壤和天然水样中存在的有机化合物引起的误差的影响。一种使用过量氧值的新方法已经显示出在 IRIS 分析中标记光谱污染植物样品的潜力。需要对这种标记系统进行系统评估，以证明其有用性。
评估甲醇和乙醇水混合物对测量的 IRIS 和同位素比质谱（IRMS）结果的诱导误差。对于 IRIS 分析，使用液体和蒸气模式（通过直接蒸气平衡）两种方法。测量了 δH、δO 和 δO 值，并与已知参考值进行比较，以确定甲醇和乙醇污染引起的误差。此外，还测试了过量氧污染检测方法。这是一种用于液体和蒸气 IRIS 三同位素分析的后处理检测工具，利用计算出的过量氧值来标记污染样品。
有机污染会导致 IRIS 结果出现显著误差，而在 IRMS 结果中则不会出现。甲醇引起的误差大于乙醇。蒸气-IRIS 分析的结果比液体-IRIS 分析的结果误差更大。过量氧方法在同位素结果变得不可接受的错误水平下，识别出了液体和蒸气模式 IRIS 样品中由甲醇驱动的误差。对于乙醇污染的样品，过量氧方法会出现错误和正确标记的混合情况。我们的结果表明，甲醇是数据损坏更严重的污染物。因此，过量氧方法对于数据质量控制非常有用。
有机污染会导致 IRIS 稳定同位素结果出现显著误差。在蒸气分析中，这些误差比在液体 IRIS 分析中更大，并且甲醇污染比乙醇污染引起的误差更大。过量氧方法对检测蒸气和液体分析模式中 IRIS 的窄带（甲醇）污染误差非常敏感。
