Development of high-performance separation methods of inorganic compounds based on aqueous biphasic extraction systems

水双相体系（ABS）是由水、某些无机盐和水溶性聚合物混合形成的，可以有效地分离无机化合物和有机化合物。聚乙二醇（PEG）无毒、不易燃、不挥发，因此与使用水不混溶有机溶剂的传统溶剂萃取系统相比，聚乙二醇基ABS可以被认为是环保的。许多研究者认为ABS中的水分子在分离过程中起着重要的作用，因此了解聚合物体系中水的状态对于阐明ABS的分离机制非常重要。因此，我们首先利用液相色谱法和差示扫描量热法研究了PEG凝胶和聚乙烯醇（PVA）凝胶中的水状态。结果表明，对于大多数PVA凝胶，固定相水的估计值与非冻结水和可冻结结合水的估计值一致，而对于PEG凝胶，固定相水的估计值与非冻结水的估计值一致。这一结果可归因于凝胶结构的差异；含有相对高浓度PVA的PVA凝胶具有均相凝胶相，而PEG凝胶具有由水合聚合物结构域和相对疏水结构域组成的非均相凝胶相。以聚乙二醇和硫酸钠为双水相体系，采用高速逆流色谱法分离无机阴离子和金属离子。采用富peg的上相作为固定相，富盐的下相作为流动相。用PEG#1000-Na_2SO_4 ABS进行HSCCC，可以很容易地分离某些无机阴离子以及铬（III）离子和铬酸盐（VI）离子。

Aqueous biphasic systems(ABS) are formed by mixing water, certain inorganic salts and water-soluble polymers and can be efficient for the separation of inorganic compounds as well as of organic compounds. Polyethylene glycols(PEG) are nontoxic, nonflammable and nonvolatile so that the PEG-based ABS can be regarded as environmentally friendly, in contrast to conventional solvent extraction systems utilizing water immiscible organic solvents. A number of investigators have considered that water molecules in ABS should play an important role in separation processes and therefore an understanding of the states of water in the polymer systems is of great importance in the elucidation of the mechanism of separation in ABS. We have thus studied, at first, the states of water in PEG gel as well as poly(vinyl alcohol)(PVA) gels by means of liquid chromatography and differential scanning calorimetry. It was found that the estimated amount of the stationary phase water is in good agreement with the sum of the amount of non-freezing water and that of freezable bound water for most of the PVA gels, while it agrees with the amount of only non-freezing water for the PEG gel. This result can be attributed to the difference in the structure of the gels ; the PVA gels containing PVA at relatively high concentrations have a homogeneous gel phase, whereas the PEG gel have a heterogeneous gel phase consisting hydrated polymer domains and relatively hydrophobic domains.Separation of inorganic anions and metal ions was investigated using high-speed countercurrent chromatography with aqueous biphasic systems consisting of PEG and sodium sulfate. The PEG-rich upper phase was used as the stationary phase and the salt-rich lower phase was used as the mobile phase. Separation of some inorganic anions and that of chromium(III) ion and chromate(VI) ion were easily accomplished by HSCCC with PEG#1000-Na_2SO_4 ABS.