Department of Chemistry, Umeå University , SE-901 87 Umeå, Sweden.
Environ Sci Technol. 2013 Aug 6;47(15):8557-64. doi: 10.1021/es304630a. Epub 2013 Jul 19.
The properties of iron (Fe) complexes and compounds in the environment influence several central processes, e.g., iron uptake, adsorption/desorption of contaminants and nutrients, and redox transformations, as well as the fate of of natural organic matter (NOM). It is thus important to characterize Fe species in environmental samples. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy has been used in several studies on soils and sediments, but literature is scarce on investigations of natural waters because of low Fe concentrations. In this study we have described a gentle and noninvasive preconcentration method, based on electrostatic adsorption onto ion-exchange resins, suitable for EXAFS analysis of Fe species in dilute stream water samples. The EXAFS results of metal-organic model complexes showed that no significant local structural distortions were induced by the method. We also demonstrated the feasibility for an 8 μM Fe stream water sample. The Fe heterogeneity in this stream water was investigated via a gradient series at 28%, 42%, 77%, 84%, and 100% adsorption of total iron. The EXAFS results showed that Fe(III) in this stream water was divided into Fe(III)-NOM complexes and Fe(III) (oxyhydr)oxides associated with NOM, and that each class consisted of several subspecies.
铁（Fe）配合物和化合物在环境中的性质影响着几个核心过程，例如铁的摄取、污染物和养分的吸附/解吸以及氧化还原转化，以及天然有机物（NOM）的命运。因此，对环境样品中的铁物种进行表征非常重要。基于同步加速器的扩展 X 射线吸收精细结构（EXAFS）光谱已在一些土壤和沉积物研究中得到应用，但由于铁浓度低，关于天然水的研究文献很少。在这项研究中，我们描述了一种温和且非侵入性的预浓缩方法，基于静电吸附到离子交换树脂上，适用于 EXAFS 分析稀流水样品中的铁物种。金属有机模型配合物的 EXAFS 结果表明，该方法不会引起明显的局部结构变形。我们还证明了对 8 μM Fe 流水样品进行分析的可行性。通过在 28%、42%、77%、84%和 100%总铁吸附的梯度系列中，研究了该流水样中的铁不均匀性。EXAFS 结果表明，该流水样中的 Fe(III)分为与 NOM 结合的 Fe(III)-NOM 配合物和 Fe(III)（氧氢）氧化物，并且每一类都由几个亚物种组成。
