Alkylsilane-based stationary phases via a displaceable surface template approach: Synthesis, characterization, and chromatographic performance

A method is presented for the preparation of silica-based alkylsilane stationary phases using octanol as a displaceable surface template to control the rate of alkylsilane condensation with the silica surface, and thereby, the resulting alkylsilane surface coverage. This method improves upon conventional preparation schemes by allowing alkylsilane stationary phases of systematically varying surface coverage to be prepared from a single reaction mixture and a single precursor molecule without rigorous control of water content of the solution or of the silica. Octadecylsilane stationary phases ranging in surface coverage from ∼3.5 to 6.0 μmol/m² were synthesized using one set of experimental conditions with variation of only the octadecylsilane/ octanol ratio. The conformational order of the octadecylsilane alkyl chains was assessed using Raman spectroscopy and was found to increase with increasing surface coverage in a manner similar to stationary phases prepared by conventional routes. As chromatographic stationary phases in microbore columns for the reversed-phase separation of monosubstituted aromatic compounds, the performance of these materials is comparable to or better than that of commercially available octadecylsilane stationary phases under identical chromatographic conditions. Furthermore, the high-density stationary phases (> 3.5 μmol/m²) prepared by this route exhibit geometric shape selectivity comparable to or better than that reported earlier for high-density octadecylsilane stationary phases prepared using conventional methods.