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-CO(2)) as a bonding medium. We present results that demonstrate that alkyl (C(8) and C(10)) and phenyl (pentafluorophenylpropyl, PFPP) silica bonded stationary phases can be prepared under sc-CO(2) conditions of 100 degrees C, 414bar and 3h, 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 (29)Si cross polarisation magic angle spinning (CP-MAS) NMR spectroscopy. In addition, the sc-trichloro prepared fluorinated C(8) 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 alpha(TBN/BaP)=1.0. These chromatographic findings are indicative of a fluorinated C(8) silica bonded stationary phase that is capable of some shape recognition.