以冷媒R134a萃取金屬螯合物

Abstract

水溶性的金屬離子在添加適當的有機螯合劑作用後，可用有機溶劑從水中萃取出，然而萃取過後的大量有機溶劑，變成新的問題待處理。超臨界流體可以取代傳統有機溶劑進行萃取，並且在收集的過程一經洩壓便可氣化與萃取物分離，達到濃縮的效果，大幅地減少樣品處理體積。本實驗嘗試以液態冷媒R134a（1,1,1,2-tetrafluoroethane）取代受到廣泛應用的超臨界二氧化碳，將操作壓力條件降低了100個大氣壓以上，同時保有足夠的溶解能力。超臨界二氧化碳對極性物質的溶解力不高，必須使用氟化的樣品才有顯著的溶解力，或是加入修飾劑以提升萃取物的溶解度，這個問題在使用R134a時獲得改善。近來有研究指出添加介面活性劑能夠增進萃取效益，甚至可以由介面活性劑與水形成的微乳液直接萃取金屬離子，而不必添加螯合劑，在本研究中亦證實可行，這對於萃取複雜基質中的金屬離子具有重要的意義。由吸收光譜測得的收集液濃度，經過計算完成定量工作，得到的資訊包括溶解度、分配係數，以及樣品中的萃取回收比例。

Hydrophilic metal ions can be extracted from aqua by organic solvent with proper organic chelating agent. Nevertheless, a new problem comes from the great volume of organic solvent containing metal ions. Supercritical fluids can replace conventional organic solvents in extraction process. When degassing at collecting, such fluids separate from extracts suddenly and concentrate them, which can reduce the waste volume. We try to use R134a (1,1,1,2-tetrafluoroethane) instead of supercritical carbon dioxide, a widely utilized solvent, and recognize that R134a has appreciable solvency while the working pressure is 100 atm lowered. Polar compounds showed low solubility in SF-CO2, unless fluorinated compounds or modifier are used, but this drawback is overcome in using R134a. Recent researches show that adding surfactant during extraction improves efficiency and even metal ions can be extracted through microemulsion without chelating agent, we also prove this idea in our experiment. This is momentous for metal ions extraction from a complicated matrix. Quantitative calculation is based on UV/Vis absorbance data; information herein includes solubility, partition coefficient and recovery of sample extraction.