Burba Peter, Van den Bergh Johan
Institute of Spectrochemistry and Applied Spectroscopy, Bunsen-Kirchhoff-Str. 11, 44139 Dortmund, Germany.
Anal Bioanal Chem. 2004 Mar;378(6):1637-43. doi: 10.1007/s00216-003-2467-z.
Transformations of metal species (particularly Al, Ca, Fe, Mg, Mn, Zn) in ageing humic hydrocolloids were studied, applying a competitive ligand and metal exchange approach. For this purpose, metal-containing hydrocolloids, freshly collected from humic-rich German bog lake waters (Hohlohsee (HO), Black Forest; Venner Moor (VM), Muensterland; Arnsberger Wald (AW), Northrhine-Westfalia) and conventionally pre-filtered through 0.45 microm membranes, were subjected on-site to an exchange with EDTA and Cu(II) ions, respectively, as a function of time. EDTA complexes gradually formed, metal fractions exchanged by Cu(II) (as well as free Cu(II) concentrations) were operationally discriminated by means of a small time-controlled tangential-flow ultrafiltration unit (nominal cutoff: 1 kDa). Metal and DOM (dissolved organic matter) fractions obtained this way were determined off-site using instrumental methods (AAS, ICP-OES, carbon analyzer). After weeks of storage, the collected hydrocolloids were studied again by this approach. The EDTA availability of colloid-bound metals (particularly Al and Fe) exhibited different ageing trends, dependent on the sample (VM: decrease of Fe availability (98-76%), HO: increase of Fe availability (76-82%)). In contrast, the Cu(II) exchange equilibria of colloid-bound metals revealed merely low availability of Al (16-38%) and Fe (5-11%) towards Cu(II) ions, also dependent on ageing effects. In particular, the conditional copper exchange constants Kex obtained from the exchange between Cu(II) ions and available metal species (such as Ca, Mg, Mn, Zn) exhibited a strong decrease (by a factor of 2-100) during sample storage, indicating considerable non-equilibria complexation of these metal ions in the original bogwaters studied on-site.
采用竞争配体和金属交换方法，研究了老化腐殖质水胶体中金属物种（特别是铝、钙、铁、镁、锰、锌）的转化。为此，从富含腐殖质的德国沼泽湖水中（黑森林地区的霍洛湖（HO）；明斯特兰地区的文纳沼地（VM）；北莱茵 - 威斯特法伦州的阿恩斯贝格森林（AW））新鲜采集并经0.45微米滤膜常规预过滤的含金属水胶体，在现场分别与乙二胺四乙酸（EDTA）和铜（II）离子进行不同时间的交换。EDTA络合物逐渐形成，通过一个小型时间控制的切向流超滤装置（标称截留分子量：1 kDa）对被铜（II）交换的金属组分（以及游离铜（II）浓度）进行操作区分。通过这种方式获得的金属和溶解性有机物（DOM）组分在实验室使用仪器方法（原子吸收光谱法（AAS）、电感耦合等离子体发射光谱法（ICP - OES）、碳分析仪）进行测定。在储存数周后，再次用这种方法对采集的水胶体进行研究。胶体结合态金属（特别是铝和铁）的EDTA有效性呈现出不同的老化趋势，这取决于样品（VM：铁有效性降低（98% - 76%），HO：铁有效性增加（76% - 82%））。相比之下，胶体结合态金属的铜（II）交换平衡显示，铝（16% - 38%）和铁（5% - 11%）对铜（II）离子的有效性仅处于较低水平，这也取决于老化效应。特别是，从铜（II）离子与可利用金属物种（如钙、镁、锰、锌）之间的交换获得的条件铜交换常数Kex在样品储存期间显著降低（降低了2 - 100倍），这表明在现场研究的原始沼泽水中，这些金属离子存在相当程度的非平衡络合。
