Effect of silane reagent functionality for fluorinated alkyl and phenyl silica bonded stationary phases prepared in supercritical carbon dioxide

This research examines the effect of silane reagent functionality for the preparation of fluorinated alkyl silica-bonded stationary phases prepared using supercritical carbon dioxide (sc-CO2) as a bonding medium. We present results that demonstrate that alkyl (C8 and C10) and phenyl (pentafluorophenylpropyl, PFPP) silica bonded stationary phases can be prepared under sc-CO2 conditions of 100 °C, 414 bar and 3 h, with surface coverages comparable to those obtained using organic solvent based methods. Fluorinated alkyl silica bonded phase preparation with a trichloro silane generates high ligand densities and more chemically uniform silica surface species compared to phases prepared using a monochloro or alkoxy silanes, as evidenced by thermogravimetric analysis (TGA) and 29Si cross polarisation magic angle spinning (CP-MAS) NMR spectroscopy. In addition, the sc-trichloro prepared fluorinated C8 bonded phases have demonstrated the ability to separate solutes on the basis of their molecular shape with the separation of the LC column shape selectivity test mixture, SRM 869a in the elution order of PhPh < BaP = TBN with a selectivity value of αTBN/BaP = 1.0. These chromatographic findings are indicative of a fluorinated C8 silica bonded stationary phase that is capable of some shape recognition.