PREPARATION AND SELECTIVITY CHARACTERISTICS OF FLUOROCARBONACEOUS BONDED STATIONARY PHASE FOR REVERSE-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

1 H, 1 H, 2 H, 2 H, 3 H, 3 H-Tridecafluoro(4,4-dimethylheptyl)silanes [3a approximately 3c] were prepared from the corresponding polyfluoroalkene [1] and silanes HSiXY2 {2a ; X = Y = Cl, 2b ; X = Cl, Y = CH3, 2c ; X = Y = OCH3] in the presence of hexachloroplatinic(IV) acid in good yields (71 approximately 90% ; Scheme 1 and Table 1). The product silanes [3a, 3b] and Dimethyl-(1 H, 1 H, 2 H, 2 H-tridecafluorooctyl)-chlorosilane [4] were used to prepare the corresponding new-type branched- and straight-fluorocarbonaceous bonded stationary phase (PES) for reverse-phase high-performance liquid chromatography (RP-HPLC). These three PFS phases were characterized by means of diffuse reflection FT-IR spectra (Fig. 1) a scanning electron microscope (Fig. 2), a combustion analysis (Table 2), nitrogen adsorption isotherms (Table 3), and RP-HPLC (Table 4, Figs. 3, 4). According to their chromatographic behavior, PFS phases showed an increased selectivity over the octadecyl bonded phase (ODS) for fluoro-, 1,2-difluoro-, 1,2,4-trifluoro-, pentafluoro-, and hexa-fluorobenzenes, especially for fluoro- and 1,2-difluorobenzenes ; and for uracil and 5-fluorouracil. In addition, the [3b]-bonded PFS phase showed superior recognition over both the PFS-[4] and ODS phases for 1,3- and 1,4-bis(2,2,2-trifluoro-1-hydroxy-1-trifluoromethyl)benzenes (Table 5, Fig. 5). These increased selectivity of PFS for the fluorinated solutes are discussed on the basis of a hydrophobic and/or organophobic interaction between the stationary phase and the solutes.