Metal Extraction from Water and Organic Solvents into Fluorous Solvents by Fluorinated β-Diketone and Its Application to the Colorimetric Analysis of Metal Ions

A metal extraction system using fluorous solvents has been developed. Perfluorinated β-diketone, 1,1,1,5,5,6,6,6-octafluoro-2,4-hexanedione (C₆F₈βDK) dissolves in the fluorous solvent FC-72 and can extract transition metal ions from water into FC-72. The extraction efficiency in the FC-72 system is comparable to that of chloroform. By using the immiscibility of FC-72 with conventional organic solvents, metal extraction was also achieved from acetonitrile and dioxane. Metal ions extracted into FC-72 can be readily stripped using 1 M nitric acid. We succeeded in a colorimetric assay of metal ion concentration in water and in organic solvents by contacting each solvent with FC-72 containing C₆F₈βDK. Iron ions with different concentrations (0 - 0.1 mM) in water or acetonitrile are completely extracted into FC-72 to form a Fe³⁺-C₆F₈βDK complex, which can be detected by spectrophotometry due to its absorption in the UV-vis region. We have demonstrated that fluorous solvents would be promising candidates for a novel separation and analytical medium for metal ions.