Department of Earth and Environmental Sciences, KU Leuven, Kasteelpark Arenberg 20 bus 2459, 3001, Leuven, Belgium.
Service Trace Elements & Nanomaterials, Sciensano, Leuvensesteenweg 17, 3080, Tervuren, Belgium.
J Chromatogr A. 2019 Aug 16;1599:203-214. doi: 10.1016/j.chroma.2019.04.032. Epub 2019 Apr 15.
Colloidal iron(III) oxyhydroxides (FeOx) are important reactive adsorbents in nature. This study was set up to determine the size of environmentally relevant FeOx colloids with new methods, i.e. Flow Field Flow Fractionation (FlFFF-UV-ICP-MS) and single-particle ICP-MS/MS (sp-ICP-MS) and to compare these with standard approaches, i.e. dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), microscopy (TEM), membrane filtration, centrifugation and dialysis. Seven synthetic nano- and submicron FeOx with different mineralogy and coating were prepared and two soil solutions were included. The FlFFF was optimized for Fe recovery, yielding 70-90%. The FlFFF determines particle size with high resolution in a 1 mM NHHCO (pH 8.3) background and can detect Fe-NOM complexes <5 nm and organo-mineral FeOx particles ranging 5-300 nm. The sp-ICP-MS method had a size detection limit for FeOx of about 32-47 nm. The distribution of hydrodynamic diameters of goethite particles detected with FlFFF, NTA and DLS were similar but the values were twice as large as the Fe cores of particles detected with sp-ICP-MS and TEM. Conventional fractionation by centrifugation and dialysis generally yielded similar fractions as FlFFF but membrane filtration overestimated the large size fractions. Particles formed from Fe(II) oxidation in the presence of NOM showed strikingly smaller organo-mineral Fe-Ox colloids as the NOM/Fe ratio increased. The soil solution obtained with centrifugation of an acid peat was dominated by small (<30 nm) Fe-OM complexes and organo-mineral FeOx colloids whereas that of a mineral pH neutral soil mainly contains larger (30-200 nm) Fe-rich particles. The FlFFF-UV-ICP-MS is recommended for environmental studies of colloidal FeOx since it has a wide size detection range, it fractionates in an environmentally relevant background (1 mM NHHCO) and it has acceptable element recoveries.
胶体三价铁氢氧化物 (FeOx) 是自然界中重要的反应性吸附剂。本研究旨在使用新方法，即流动场流分级 (FlFFF-UV-ICP-MS) 和单颗粒 ICP-MS/MS (sp-ICP-MS)，确定具有环境相关性的 FeOx 胶体的粒径，并将其与标准方法，即动态光散射 (DLS)、纳米颗粒跟踪分析 (NTA)、显微镜 (TEM)、膜过滤、离心和透析进行比较。制备了七种具有不同矿物学和涂层的合成纳米和亚微米级 FeOx，并包含两种土壤溶液。FlFFF 对 Fe 回收率进行了优化，回收率为 70-90%。FlFFF 在 1 mM NH4HCO (pH 8.3) 背景下以高分辨率确定粒径，并能检测 <5nm 的 Fe-NOM 配合物和 5-300nm 的有机-矿物 FeOx 颗粒。sp-ICP-MS 方法对 FeOx 的粒径检测下限约为 32-47nm。FlFFF、NTA 和 DLS 检测到的针铁矿颗粒的水动力直径分布相似，但值是 sp-ICP-MS 和 TEM 检测到的颗粒 Fe 核的两倍大。离心和透析的常规分级通常产生与 FlFFF 相似的级分，但膜过滤高估了大粒径级分。在 NOM 存在下 Fe(II)氧化形成的颗粒表现出明显更小的有机-矿物 Fe-Ox 胶体，随着 NOM/Fe 比的增加而增加。用离心法从酸性泥炭中提取的土壤溶液主要由小(<30nm)的 Fe-OM 配合物和有机-矿物 FeOx 胶体组成，而中性 pH 矿物土壤的溶液主要含有较大的(30-200nm)富铁颗粒。FlFFF-UV-ICP-MS 推荐用于胶体 FeOx 的环境研究，因为它具有较宽的粒径检测范围，在具有环境相关性的背景下进行分级 (1mM NH4HCO)，并且具有可接受的元素回收率。
