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

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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.