Extraction method using thermo-responsive polymer : equilibrium analysis, and new enrichment technique for trace metals

一些水溶性聚合物，包括聚乙烯基甲基醚（PVME），在水溶液中表现出较低的临界溶解温度（LCST）（PVME约为308 K）。它们在低温下是水溶性的，但在温度以上加热会导致相分离。通过相分离，将水溶液中的某些疏水物质有效地掺入到聚合物相中，从而使这种热响应性聚合物可以作为萃取介质。本文研究了在323 K温度下8-喹啉酸盐金属螯合物体系和四烷基铵盐体系的离子对在温度诱导的PVME分离相中的分布平衡。通过对分布数据的分析，我们可以阐明分布平衡和提取常数K_<ex>的值。为了弄清聚合物相的性质，将聚合物介导萃取的结果与传统溶剂萃取的结果进行了比较。此外，我们还开发了一种新的热响应聚合物（PVME）预富集技术来测定痕量金属离子。作为该技术的典型案例，我们建立了将苦味酸离子铜-新根碱螯合物的离子对定量萃取到体积极小的聚合物相的最佳条件。将聚合物相溶于少量丙酮中，用石墨原子吸收光谱法对溶液进行分析。该方法可用于海水中铜的测定。

Some kind of water-soluble polymers, including poly (vinyl methyl ether)(PVME), in aqueous solutions exhibit a lower critical solution temperature (LCST)(for PVME around 308 K). They are water-soluble at low temperatures but their heating above the LCST results in phase separation. By the phase separation, certain hydrophobic substances in aqueous solution are efficiently incorporated into the polymer phase, and thus, such thermo-responsive polymers can be used as an extracting medium.In this study, the distribution equilibria of 8-quinolinolate metal chelates system and ion pairs of tetraalkylammonium salts system into temperature-induced separation phase of PVME have been investigated at 323 K. From an analysis of the distribution data, we can elucidate the distribution equilibria, and values of the extraction constant, K_<ex>. These results of polymer-mediated extraction were compared with those in conventional solvent extraction in order to clarify the natures of the polymer phase.Moreover, we have developed new preconcentration technique using themo-responsive polymer (PVME) for the determination of trace metal ions. As the model case of this technique, we established the optimum conditions for quantitave extraction of the ion pair of the copper-neocuproine chelate with picrate ion into the polymer phase having the very small volume. After dissolving the polymer phase in a small amount of acetone, the solution was analyzed by graphite AAS. This method was successfully applicable to the determination of copper in sea water.