亚临界水萃取在分析化学中的应用

亚临界水的介电常数ε随温度增加而减少，在250℃时ε值只有27（介于甲醇与乙醇之间），比常温常压下下水的介电常数ε＝80下降了许多。亚临界水极性的减弱，使它对中极性和非极性有机化合物的溶解度大大增加，可以定量萃取出固体试样中的多环芳烃和多氯联苯化合物。另外，亚临界水也可以作为反相高效液体色谱的洗脱液。

Application of Subcritical Water Extraction in Analytical Chemistry

At ambient temperature and pressure water has a dielectric constantε = 80. However, I he dielectric constant of subcritical water can be lowerd by raising the temperature of the water under moderate pressure. Subcritical water at 250 ℃ and 5 MPa hasε = 27,which is similar to those of ethanol (ε = 24) and methanol (ε = 33). Thus,the solubilities of low polarity organics such as PAHs and PCBs can be increased by heating the water under moderate pressure. Furthermore,subcritical water has been shown to be a feasible medium polarity replacement for methanol-water or acetonitrile-water mixture as an eluent for reversed-phase HPLC.