Sol-gel-derived fluorinated stationary phase for open tubular electrochromatography

We report on the preparation of a sol-gel-derived fluorinated stationary phase using a 13 μm I.D. fused-silica capillary for open tubular electrochromatography (OTEC). The sol-gel-derived fluorinated column is prepared by hydrolyzing a mixture of tetraethoxysilane (TEOS) and tridecafluoro-1,1,2,2-tetrahydrooctyl-1-triethyoxysilane (F₁₃-TEOS) followed by coating a thin film onto the inner walls of a fused-silica capillary. The retention characteristics of the sol-gel-derived fluorinated column are compared with a sol-gel-derived octylhydrocarbonaceous (C₈) column. Using the sol-gel-derived fluorinated column, we report on the successful separation of six model fluorinated organic compounds which cannot be separated using the C₈ column prepared either via sol-gel method or by conventional methods. We achieved high efficiencies of 100,000-300,000 plates/m for the various model fluorinated compounds using the sol-gel-derived fluorinated column. We have also investigated the separation performance of the sol-gel-derived fluorinated column using different TEOS:F₁₃-TEOS ratios and the optimum reaction time before column coating. Optimum selectivity was obtained with a TEOS:F₁₃-TEOS molar ratio of 1:2 reacted for 24 h prior to column coating.