Burba P, Van den Bergh J, Klockow D
Institute of Spectrochemistry and Applied Spectroscopy, Dortmund, Germany.
Fresenius J Anal Chem. 2001 Nov;371(5):660-9. doi: 10.1007/s002160101013.
Humic-rich hydrocolloids and their metal loading in selected German bog-waters have been characterized by a novel on-site approach. By use of an on-line multistage ultrafiltration (MST-UF) unit equipped with conventional polyethersulfone (PES)-based flat membranes (nominal cut-off 0.45, 0.22, and 0.1 microm, or 100, 50, 10, 5, 3 kDa) the hydrocolloids could be fractionated on-site in both sub-particulate and macromolecular size ranges. Characterization (dissolved organic carbon (DOC), metals) of the colloid fractions obtained this way was performed off-site by use of conventional instrumental methods (carbon analyzer, AAS, ICP-OES, and TXRF (total reflection X-ray fluorescence)). Major DOC fractions of the hydrocolloids studied were found to be in the size range <5 kDa. The assessed metals (Al, Cu, Fe, Mn, Pb, and Zn) were, however, predominantly enriched in the macromolecular and sub-particulate range, depending on the metal and the sample, respectively. In addition, metal species bound to these hydrocolloids were kinetically characterized on-site by use of competitive ligand (EDTA (ethylenediaminetetraacetate)) and metal (Cu(II)) exchange; the EDTA complexes formed and the metal ions exchanged were separated by means of a small time-controlled tangential-flow UF unit (cut-off 1 kDa). Bound metal fractions, in particular Al and Fe, reacted only slowly (500 to 1000 min) with EDTA; the conditional availability was 60-99%, depending on the hydrocolloid. In contrast, the Cu(II) exchange of colloid-bound metal species approached equilibrium within 5-10 min, with characteristic exchange constants, Kex, of the order of 0.01 to 90 for the metals (Fe<Al<Zn<Mn approximately/= Ca approximately/= Mg). The results were clearly dependent on the water investigated. Thus detailed information on the conditional kinetic and thermodynamic stability of colloid-bound metal species could be obtained from competitive EDTA and Cu(II) exchange under on-site conditions.
采用一种新型现场方法对德国特定沼泽水中富含腐殖质的水胶体及其金属负载情况进行了表征。通过使用配备传统聚醚砜（PES）基平板膜（标称截留分子量为0.45、0.22和0.1微米，或100、50、10、5、3 kDa）的在线多级超滤（MST-UF）装置，可在现场将水胶体按亚颗粒和大分子尺寸范围进行分级。通过使用传统仪器方法（碳分析仪、原子吸收光谱法、电感耦合等离子体发射光谱法和全反射X射线荧光光谱法（TXRF））在现场外对以此方式获得的胶体级分进行表征（溶解有机碳（DOC）、金属）。研究发现，所研究水胶体的主要DOC级分在<5 kDa的尺寸范围内。然而，所评估的金属（铝、铜、铁、锰、铅和锌）分别根据金属和样品的不同，主要富集在大分子和亚颗粒范围内。此外，通过使用竞争性配体（乙二胺四乙酸（EDTA））和金属（铜（II））交换在现场对与这些水胶体结合的金属物种进行动力学表征；形成的EDTA络合物和交换的金属离子通过一个小型时间控制切向流超滤装置（截留分子量1 kDa）进行分离。结合的金属级分，特别是铝和铁，与EDTA的反应非常缓慢（500至1000分钟）；条件有效性为60 - 99%，具体取决于水胶体。相比之下，胶体结合金属物种的铜（II）交换在5 - 10分钟内达到平衡，金属（铁<铝<锌<锰≈钙≈镁）的特征交换常数Kex约为0.01至90。结果明显取决于所研究的水体。因此，在现场条件下通过竞争性EDTA和铜（II）交换可以获得有关胶体结合金属物种的条件动力学和热力学稳定性的详细信息。
