New Fluorous Reversed Phase Silica Gels for HPLC Separations of Perfluorinated Compounds

Two new perfluoroalkyl-modified stationary phases were prepared and compared with two commercially available perfluorinated stationary phases (Fluophase RP and Fluophase Pentafluorophenyl) and a C18-RP column with respect to retention times of an array of perfluoroalkyl-tagged and untagged molecules. A few highly lipophilic compounds were also included in the study. They showed high retention times on C18-RP columns, but not on perfluorinated support materials. Perfluoroalkyl-tagged compounds revealed a weak interaction with the pentafluorophenyl-modified support. The interaction between perfluoroalkyl-tagged compounds and perfluoroalkyl-modified stationary phases was strong, and dependent on the chain length of the perfluoro tags. Surprisingly, there was only a small difference between the retention times of perfluorinated compounds on C18-RP and C6F13-modified support. Fluorous-fluorous interactions became prevalent only with C8F17-tagged compounds on C8F17 functionalized silica gel. Compounds with two perfluoro tags showed a drastic increase in retention time, which might be due to a cooperative effect. These results demonstrate the uniqueness of fluorous-fluorous interactions based on linear perfluoroalkyl chains and open up possibilities for the design of new perfluoro tags for purifications and noncovalent attachments of catalysts or biomolecules on perfluorinated solid supports.