Development of temperature and pressure variable aqueous biphasic extraction system with superheated water

双水相系统（ATPS）是由水、某些无机盐和水溶性聚合物混合而成的，可用于分离各种化合物。聚乙二醇（PEG）具有无毒、不燃、不挥发等特点，因此，基于PEG的ATPS具有环境友好性，为了提高ATPS的分离选择性，扩大其应用范围，我们研制了一种可在高温下进行萃取的ATPS萃取装置。从溶质与聚合物溶液相的相互作用和盐析效应的角度研究了正醇、酮和硝基烷烃在由PEG和Na_2SO_4形成的ATPS中的分配行为。结果表明，PEG基ATPS和PEG凝胶体系的分离选择性基本相同。对PEG水溶液的差示扫描量热法研究表明，PEG聚合物形成的水合结构的组成为50%（w/w）的PEG或每个环氧乙烷的水合数为2.4和PEG-水系统的分离选择性可以归因于溶质化合物分配到水合PEG聚合物结构。此外，为了阐明聚合物疏水基团对ATPS分离选择性的贡献，还研究了无机阴离子在烷基键合硅胶柱中的保留行为。从所获得的结果，它已得出结论，溶剂化的水相形成的烷基键合的二氧化硅的表面上，并表现出不同的本体液态水的溶质化合物的亲和力。

Aqueous two-phase systems (ATPS) are formed by mixing water, certain inorganic salts and water-soluble polymers and can be useful for the separation of various compounds. Polyethylene glycol (PEG) is nontoxic, nonflammable and nonvolatile so that the PEG-based ATPS can be regarded as environmentally friendly.We have developed an ATPS extraction device which enables one to carry out extraction at elevated temperature in order to enhance the separation selectivity and expand the applicability of ATPS. The distribution behavior of n-alcohols, ketones and nitroalkanes in ATPS formed from PEG and Na_2SO_4 was investigated from the viewpoints of interaction of the solutes with the polymer solution phase and the salting-out effect. The results obtained revealed that the separation selectivities exerted by the PEG-based ATPS and the PEG gel system are approximately the same. Differential scanning calorimetry studies on aqueous PEG solutions suggested that PEG polymer forms a hydration structure of which the composition is 50 % (w/w) PEG or the hydration number per ethylene oxide is 2.4 and the separation selectivity of the PEG-water systems can be ascribed to partition of solute compounds into the hydrated PEG polymer structure. Furthermore, it has been demonstrated that the separation selectivity of the ATPS depends strongly on temperature.Furthermore, in order to clarify the contribution of hydrophobic moieties of polymers on the separation selectivity of ATPS, the retention behavior of inorganic anions in reversed-phase liquid chromatography was investigated using the columns packed with alkyl bonded silica particles. From the results obtained, it has been concluded that the solvated water phase is formed on the surface of alkyl-bonded silica and exhibits an affinity to solute compounds different from that of the bulk liquid water.