平衡渗析-多种光谱法研究太湖不同分子量溶解性有机质及其与铜的相互作用

Determination of Cu complexed with individual molecular size fractions of dissolved organic matter from the Taihu Lake,China by equilibrium dialysis and multiple spectroscopic methods

采用平衡渗析技术将太湖沉积物溶解性有机质(DOM)按分子量分成不同的组分.利用光谱技术和离子选择电极(ISE)分析了不同分子量溶解性有机质的光谱特征及对Cu的结合,进一步探讨分子量对DOM特性和对金属结合能力的影响.结果表明,南太湖DOM分子量以高于10000 Da为主,然而北太湖分子量以低于3500 Da为主.三维荧光光谱(3DEEM)表明太湖沉积物DOM呈现出4种特征荧光峰.类富里酸荧光峰的荧光强度随着DOM分子量的增加而增强,然而类蛋白质荧光峰的荧光强度随着DOM分子量的增加而降低.南太湖DOM碳氮比(C/N)(20.30)显著高于北太湖(7.58),表明了DOM不同的来源.对于南北湖区,DOM-Cu浓度最大值都是在DOM分子量低于1000 Da组分,大约50%的DOM-Cu在分子量低于3500 Da的组分中.结合容量表明南太湖DOM分子量低于3500 Da的组分和北太湖分子量在1000—3500 Da的组分对于Cu结合起主要的作用,表明低分子量DOM对于结合重金属的重要性.

Dissolved organic matter（DOM） from Taihu Lake sediment was separated into different molecular weight fractions with equilibrium dialysis. Spectroscopic methods and ion selective electrode（ISE） were employed to analyze spectral characteristics of different molecular weight DOM and the interaction with Cu,and to further examine metal-binding abilities and fluorescence signals in connection with molecular weight. The results indicated that in South Lake DOM was dominatedwith molecular weight higher than 10000 Da,while in the North Lake DOM was dominated with molecular weight lower than 3500 Da. Three-dimensional fluorescence excitation-emission matrix（3DEEM） showed that DOM from Taihu sediment displayed four distinct fluorophores peaks.Fluorescence intensity of humic-like fluorescence peak increased with the DOM molecular weight,while the fluorescence intensity of protein-like fluorescence peak decreased with the molecular weight. C / N of DOM in South Lake（20. 30） was significantly higher than that in North Lake（7.58）,indicating their different source. DOM-Cu complex concentration was maximal in the fractions with molecular weight lower than 1000 Da in both South Lake and North Lake,and around50% of the total DOM-Cu in the fractions with molecular weight lower than 3500 Da. Complexing capacity showed that DOM with molecular weight lower than 3500 Da in the South Lake and molecular weight between 1000 and 3500 Da in the North Lake were largely responsible for Cu complexing,indicating the importance of low molecular weight fractions in heavy metal binding.