Institute of Spectrochemistry and Applied Spectroscopy (ISAS), Bunsen-Kirchhoff-Str. 11, D-44139 Dortmund, Germany.
Talanta. 2001 Sep 13;55(3):587-93. doi: 10.1016/s0039-9140(01)00449-0.
The conditional metal availability and the kinetic stability of humic substance-metal species in humic-rich waters (e.g. bog water) was characterized by means of EDTA exchange. For this purpose a combined procedure consisting of time-controlled ligand exchange by EDTA, species differentiation by a fast single-stage tangential-flow ultrafiltration (TF-UF) technique (cut-off 1 kDa) and sensitive atomic spectrometry methods (e.g. AAS, ICP-OES, TXRF) was developed. The kinetics and the yield of the EDTA exchange served as operational parameters for assessing the kinetic stability and EDTA availability of HS-metal species, respectively. Considerable fractions of natural HS-metal species studied were shown to be EDTA-inert (e.g. 31% of the total Fe, 44% of the total Al) even after long reaction times (48 h), in contrast to artificial ones formed in solutions of isolated HS. Moreover, the conditional thermodynamic stability of HS-metal complexes formed by successive loading of an aquatic reference HS (HO14) with a number of heavy metal ions (e.g. Cr(III), Cu(II), Fe(III), Mn(II), Zn(II)) was also evaluated discriminating the free metal concentrations by means of TF-UF. In addition, from the loading isotherms obtained conditional complexation capacities could be derived for the studied HS exhibiting the order Fe(III)>>Cu(II)>Cr(III)>Co(II)>Mn(II).
富里酸水体（如沼泽水）中腐殖质-金属物种的条件金属可用性和动力学稳定性是通过 EDTA 交换来表征的。为此，开发了一种组合程序，包括 EDTA 的时间控制配体交换、通过快速单级切向流超滤（TF-UF）技术（截止值 1 kDa）的物种分化以及灵敏的原子光谱方法（例如 AAS、ICP-OES、TXRF）。EDTA 交换的动力学和产率分别用作评估 HS-金属物种的动力学稳定性和 EDTA 可用性的操作参数。研究表明，相当大比例的天然 HS-金属物种即使在长时间（48 小时）反应后也对 EDTA 不敏感（例如，总铁的 31%，总铝的 44%），与在分离的 HS 溶液中形成的人工 HS-金属物种形成对比。此外，还通过连续加载水生参考 HS（HO14）与多种重金属离子（例如 Cr(III)、Cu(II)、Fe(III)、Mn(II)、Zn(II)）来评估由重金属离子形成的 HS-金属配合物的条件热力学稳定性，通过 TF-UF 来区分游离金属浓度。此外，还可以从获得的加载等温线推导出研究 HS 的条件络合容量，其表现出的顺序为 Fe(III)>>Cu(II)>Cr(III)>Co(II)>Mn(II)。
