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

水两相体系（ATPS）是由水、某些无机盐和水溶性聚合物混合形成的，可用于各种化合物的分离。聚乙二醇（PEG）无毒、不易燃、不挥发，因此基于聚乙二醇的ATPS可以被认为是环保的。为了提高ATPS的分离选择性和扩大其适用性，我们研制了一种可以在高温下进行提取的ATPS萃取装置。从溶质与聚合物溶液相的相互作用和盐析作用的角度研究了正醇类、酮类和硝基烷烃在聚乙二醇和Na_2SO_4形成的ATPS中的分布行为。结果表明，PEG基ATPS和PEG凝胶体系的分离选择性大致相同。对PEG水溶液的差示扫描量热法研究表明，PEG聚合物形成了一种水化结构，其组成为50% (w/w) PEG或每环氧乙烷的水化数为2.4，PEG-水体系的分离选择性可归因于溶质化合物在水化PEG聚合物结构中的分配。此外，还证明了ATPS的分离选择性与温度密切相关。此外，为了阐明聚合物疏水部分对ATPS分离选择性的贡献，采用烷基键合二氧化硅填充柱研究了反相液相色谱中无机阴离子的保留行为。结果表明，溶剂化水相是在烷基键合二氧化硅表面形成的，对溶质化合物表现出不同于整体液态水的亲和力。

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.