ABSTRACT

Water stable isotopes have been widely used as natural tracers to investigate soil–plant–atmosphere interactions. Recent developments in induction module cavity ring-down spectroscopy (IM-CRDS) have made it possible to rapidly complete isotope analyses, and to combust co-extracted organic compounds at the same time. However, the agreement between IM-CRDS and isotope ratio mass spectrometry (IRMS) analyses has generally been poor and was primarily attributable to spectral interference of IM-CRDS. Here we evaluated the impacts of organic contamination on the isotope ratios using IM-CRDS with two different methods. No spectral interference was observed for solid samples measured directly by IM-CRDS, whereas clear organic contamination occurred in isotope analyses for pre-extracted plant stem and leaf samples. Our results demonstrate that IM-CRDS can fully combust co-extracted organic compounds by in-line oxidation in the direct measurement of solid samples, although this may not guarantee that the IM-CRDS can obtain better isotopic data than IRMS. It may be risky to evaluate the performance of IM-CRDS by measuring pre-extracted water samples because cryogenic vacuum distillation is likely to introduce extra organic compounds, which may not be fully removed during subsequent IM-CRDS measurement. In addition, spectral variables are useful for post-processing corrections.

摘要

水稳定同位素已被广泛用作天然示踪剂，以研究土壤-植物-大气之间的相互作用。感应模块腔衰荡光谱技术（IM-CRDS）的最新发展使快速完成同位素分析和同时燃烧共萃取的有机化合物成为可能。但是，IM-CRDS和同位素比质谱法（IRMS）分析之间的一致性通常很差，并且主要归因于IM-CRDS的光谱干扰。在这里，我们使用IM-CRDS和两种不同的方法评估了有机污染物对同位素比率的影响。对于通过IM-CRDS直接测量的固体样品，未观察到光谱干扰，而在预先提取的植物茎和叶样品的同位素分析中，出现了明显的有机污染。我们的结果表明，IM-CRDS可以在直接测量固体样品中通过在线氧化完全燃烧共萃取的有机化合物，尽管这可能无法保证IM-CRDS可以获得比IRMS更好的同位素数据。通过测量萃取前的水样品来评估IM-CRDS的性能可能有风险，因为低温真空蒸馏可能会引入多余的有机化合物，这些有机化合物在随后的IM-CRDS测量中可能无法完全去除。此外，频谱变量对于后期处理校正很有用。通过测量萃取前的水样品来评估IM-CRDS的性能可能有风险，因为低温真空蒸馏可能会引入多余的有机化合物，这些有机化合物在随后的IM-CRDS测量中可能无法完全去除。此外，频谱变量对于后期处理校正很有用。通过测量萃取前的水样品来评估IM-CRDS的性能可能有风险，因为低温真空蒸馏可能会引入多余的有机化合物，这些有机化合物在随后的IM-CRDS测量中可能无法完全去除。此外，频谱变量对于后期处理校正很有用。