Department of Environmental Sciences, Informatics and Statistics Ca' Foscari University of Venice, Via Torino, 155, 30172 Mestre-Venezia, Italy.
Molecules. 2019 Sep 3;24(17):3201. doi: 10.3390/molecules24173201.
Dissolved organic matter (DOM) plays an important role in the environment by influencing the transport and distribution of organic and inorganic components through different processes: the retention, mobilization, and bio-availability of potentially toxic elements (PTEs). The aim of the present study is to examine the dimensional characterization of humic acids (HA) extracted from soil matrix, as well as to analyze the metal distribution among different ligand classes. The molecular size distribution of the HA extract from soil showed three dimensional classes: 52 KDa, 4.5 KDa, and 900 Da. HPSEC-ICP-MS measurements demonstrated that the dimensional classes, relative to first two fractions, bind the largest part of metals. The complexing capacity of HA was evaluated to assess the pollutants mobility in the environmental system. In particular, cadmium (Cd) and copper (Cu) complexation was investigated due to the great concern regarding their bio-availability and toxicity in natural waters. The complexing capacity of HA solution (20 mg/L) was measured by titration using a high-performance size exclusion chromatography (HP-SEC) coupled to an inductively coupled mass spectrometry (ICP-MS). Results obtained by this technique are compared with those obtained by anodic stripping voltammetry (ASV) to investigate the effects of kinetic lability of complexes on measurements carried by HPSEC-ICP-MS. In this study, results of ligand concentrations and stability constants obtained via the two techniques are assessed considering the detection window associated to the applied analytical methodology. Results obtained using the two analytical techniques showed that Cd is complexed by two classes of ligands. However, the ligand concentration values obtained using the two techniques are different, because the detection window associated to the two methodologies; the complexing capacity, which was obtained as sum of the two classes of ligands, were 33 nmol/L and 9 nmol/L for ASV and HPSEC-ICP-MS, respectively. The copper complexing capacities determined by the two methodologies are comparable: 166 and 139 nmol/L for ASV and HPSEC-ICP-MS, respectively. However, the results of Cu titration differ for the two techniques, highlighting only one class of ligands when ASV was used, and two classes when HPSEC-ICP-MS was employed. Differences on results obtained by the two techniques are explained considering the kinetic lability of complexes; the results show that, differently from previous studies, also Cu complexes can be kinetically labile, if one technique with high reaction time is used, as well some cadmium complexes are sufficient stable to be determined by HPSEC-ICP-MS.
溶解有机质（DOM）通过不同的过程影响有机和无机成分的迁移和分布，从而在环境中发挥重要作用：潜在有毒元素（PTE）的保留、迁移和生物利用度。本研究的目的是研究从土壤基质中提取的腐殖酸（HA）的尺寸特征，并分析不同配体类别的金属分布。土壤中 HA 提取物的分子大小分布显示了三个维度的类别：52 kDa、4.5 kDa 和 900 Da。HPSEC-ICP-MS 测量表明，相对于前两个分数，尺寸类别结合了大部分金属。通过使用高效尺寸排阻色谱（HP-SEC）与电感耦合质谱（ICP-MS）耦合的滴定法评估 HA 的络合能力，以评估污染物在环境系统中的迁移能力。特别是由于 Cd 和 Cu 在天然水中的生物利用度和毒性，研究了它们的络合。通过使用高效尺寸排阻色谱（HP-SEC）与电感耦合质谱（ICP-MS）耦合的滴定法测量 HA 溶液（20 mg/L）的络合能力。通过阳极溶出伏安法（ASV）获得的结果进行比较，以研究络合物的动力学不稳定性对通过 HPSEC-ICP-MS 进行的测量的影响。在这项研究中，通过两种技术获得的配体浓度和稳定性常数的结果是根据与所应用的分析方法相关的检测窗口进行评估的。使用两种分析技术获得的结果表明，Cd 与两类配体络合。然而，使用两种技术获得的配体浓度值不同，因为与两种方法相关的检测窗口；通过两种方法获得的络合能力，分别为 33 nmol/L 和 9 nmol/L。通过两种方法确定的铜络合能力是可比的：ASV 和 HPSEC-ICP-MS 分别为 166 和 139 nmol/L。然而，两种技术的 Cu 滴定结果不同，当使用 ASV 时仅检测到一类配体，而当使用 HPSEC-ICP-MS 时检测到两类配体。考虑到络合物的动力学不稳定性，对两种技术获得的结果的差异进行了解释；结果表明，与以前的研究不同，即使使用具有高反应时间的一种技术，某些 Cu 络合物也可能具有动力学不稳定性，而一些 Cd 络合物足够稳定，可以通过 HPSEC-ICP-MS 来确定。
