Aster B, Burba P, Broekaert J A
Institute for Spectrochemistry and Applied Spectroscopy, Postfach 10 1352, D-44139, Dortmund, Germany.
Anal Bioanal Chem. 1996 Mar;354(5-6):722-8. doi: 10.1007/s0021663540722.
The molecular-size fractionation of aquatic humic substances (HS) and their metal species by means of a novel sequential-stage ultrafiltration (UF) device equipped with five appropriate ultramembranes (1, 5, 10, 50 and 100 kD) is described. First of all, the concentration dynamics of macromolecules, particulary HS, during five-stage UF and its subsequent washing step has been modelled. Based on these results, the fractionation of aquatic HS (from ground and bog water) by means of multistage UF has been optimized for an analytical scale (10 ml sample, 1 mg/ml HS, 10 ml washing solution, pH 6.0). The molecular size-distribution of selected aquatic HS (BOC 1/2 from the "DFG-Versuchsfeld Bocholt", VM 5 from "Venner Moor", Germany) studied by five-stage UF exhibited strong systematic influences of the procedure used for their isolation. The molecular-size distribution of HS obtained by on-line UF and gel permeation chromatography (GPC) showed a satisfactory agreement in the range 1-50 kD. Moreover, when interrupting multistage UF for > 48 h a slow transformation in the HS samples has been found as gradually additional HS fractions of < 1 kD have been formed. Besides unloaded HS molecules, the molecular-size distribution of freshly formed metal species of HS (1.0 mg metal/g HS of Al(III), Cd(II), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Zn(II), each) has been characterized by multistage UF as a function of pH-value, degree of loading and complexation time. Metal determinations as carried out by flame AAS, showed that considerable metal fractions in HS especially are present in molecules > 50 kD, which seemed to be rather acid-inert. With complexation times of < 2 days a transient shift of the molecular size distribution of both HS and their metal species (e.g., Al(III), Fe(III) to higher values (> 10 kD) has been found.
本文描述了通过配备五个合适超滤膜（1、5、10、50和100 kD）的新型连续阶段超滤（UF）装置对水生腐殖质（HS）及其金属形态进行分子大小分级分离的方法。首先，对五阶段超滤及其后续洗涤步骤中大分子（特别是HS）的浓度动态进行了建模。基于这些结果，针对分析规模（10 ml样品、1 mg/ml HS、10 ml洗涤液、pH 6.0）优化了通过多级超滤对水生HS（来自地下水和沼泽水）的分级分离。通过五阶段超滤研究的选定水生HS（来自德国“DFG-Versuchsfeld Bocholt”的BOC 1/2、来自“Venner Moor”的VM 5）的分子大小分布显示，其分离所用程序具有强烈的系统影响。通过在线超滤和凝胶渗透色谱（GPC）获得的HS分子大小分布在1-50 kD范围内显示出令人满意的一致性。此外，当多级超滤中断超过48小时时，发现HS样品中发生了缓慢的转化，因为逐渐形成了小于1 kD的额外HS级分。除了未负载的HS分子外，通过多级超滤对HS新形成的金属形态（每种1.0 mg金属/g HS的Al(III)、Cd(II)、Cu(II)、Fe(III)、Mn(II)、Ni(II)、Pb(II)、Zn(II)）的分子大小分布进行了表征，作为pH值、负载程度和络合时间的函数。通过火焰原子吸收光谱法进行的金属测定表明，HS中相当一部分金属尤其存在于大于50 kD的分子中，这些分子似乎对酸相当惰性。在络合时间小于2天时，发现HS及其金属形态（例如，Al(III)、Fe(III)）的分子大小分布发生了向更高值（> 10 kD）的瞬时偏移。
