Ndungu Kuria, Hurst Matthew P, Bruland Kenneth W
Department of Applied Environmental Science (ITM), Stockholm University, S-106 91 Stockholm, Sweden.
Environ Sci Technol. 2005 May 1;39(9):3166-75. doi: 10.1021/es0483948.
The supported liquid membrane (SLM) is a promising separation and preconcentration technique that is well-suited for trace metal speciation in natural waters. The technique is based on the selective complexation of metal ions by a hydrophobic ligand (carrier) dissolved in a water-immiscible organic solvent immobilized in a porous, inert membrane. This membrane separates two aqueous solutions: the test (or donor) solution and the strip (or acceptor) solution. The metal carrier complex is transported by diffusion across the membrane from the source to the strip solution where metal ions are back-extracted. The technique offers great potential to tune the selectivity by incorporating different complexing ligands in the membrane. A SLM was used to analyze the dissolved (<0.45 microm) copper speciation from two sites in the San Francisco Bay estuary; Dumbarton Bridge, [Cu]total approximately 27 nM, and San Bruno Shoals, [Cu]total approximately 23 nM. The sites were also characterized independently by differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE). The SLM employed 10 mM lasalocid, a naturally occurring carboxylic polyether ionophore, in nitrophenyl octyl ether (NPOE) asthe membrane complexing ligand, supported by a microporous, polypropylene, hydrophobic membrane. This is the first study where SLM technique has been compared with an independent speciation technique in marine waters. Results of copper speciation measurements from Dumbarton Bridge, a site in South San Francisco Bay where copper speciation has been well-characterized in previous studies using various voltammetric techniques, indicated that only about 3% (0.9 nM) of the total dissolved copper was SLM labile. The corresponding DPASV labile copper fraction was <0.4% (<0.1 nM) of total dissolved copper. The concentration of total copper binding ligands measured by the membrane technique was 471 nM as compared to 354 nM measured by DPASV, more than 1 order of magnitude higher than the total dissolved copper concentration. The SLM measurements were consistent with earlier copper speciation measurements that were made in South San Francisco Bay using other voltammetric stripping techniques.
支撑液膜（SLM）是一种很有前景的分离和预浓缩技术，非常适合用于天然水体中痕量金属的形态分析。该技术基于溶解在与水不混溶的有机溶剂中的疏水配体（载体）对金属离子的选择性络合作用，这种有机溶剂固定在多孔惰性膜中。该膜将两种水溶液隔开：测试（或供体）溶液和反萃（或受体）溶液。金属载体络合物通过扩散穿过膜从源溶液传输到反萃溶液，在反萃溶液中金属离子被反萃出来。通过在膜中加入不同的络合配体，该技术在调节选择性方面具有很大潜力。使用支撑液膜分析了旧金山湾河口两个地点溶解态（<0.45微米）铜的形态；邓巴顿桥，总铜含量约为27纳摩尔，以及圣布鲁诺浅滩，总铜含量约为23纳摩尔。这些地点还使用涂有Nafion的薄汞膜电极（NCTMFE）通过差分脉冲阳极溶出伏安法（DPASV）进行了独立表征。支撑液膜使用10毫摩尔的拉沙洛西（一种天然存在的羧酸聚醚离子载体），以硝基苯基辛醚（NPOE）作为膜络合配体，由微孔聚丙烯疏水膜支撑。这是首次在海水中将支撑液膜技术与独立的形态分析技术进行比较的研究。来自邓巴顿桥（旧金山湾南部的一个地点，此前使用各种伏安技术对该地点的铜形态进行了充分表征）的铜形态测量结果表明，总溶解铜中只有约3%（0.9纳摩尔）是支撑液膜易变的。相应的DPASV易变铜部分占总溶解铜的<0.4%（<0.1纳摩尔）。通过膜技术测得的总铜结合配体浓度为471纳摩尔，而通过DPASV测得的为354纳摩尔，比总溶解铜浓度高出1个多数量级。支撑液膜测量结果与此前在旧金山湾南部使用其他伏安溶出技术进行的铜形态测量结果一致。
