Preparation of stationary phases for reversed-phase high-performance liquid chromatography using thermal treatments at high temperature

Batches of poly(methyloctylsiloxane) (PMOS)-loaded silica were prepared by deposition from a solution of PMOS into the pores of HPLC silica. Portions of PMOS-loaded silica were subjected to a thermal treatment at 100 °C for 24 h (condition 1) in a tube furnace under a nitrogen atmosphere. After that, the material was heated for 4 h at higher temperatures (150–400 °C) (condition 2). Heating at higher temperatures produces polymer bilayers. Non-immobilized and thermally treated stationary phases were characterized by percent carbon, 29Si cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy and reversed-phase chromatographic performance. The results show that thermal treatment between 150 and 300 °C accelerates the immobilization process, possibly due to some bond breaking of the polysiloxane, with formation of strong linkages to the surface of the support, resulting in more complete coverage of the silica. The chromatographic results show an improvement of efficiency with the increase of the temperature of condition 2 up to 300 °C and an increase in the resolution of the components, mainly for the phase heated at 300 °C. Such results demonstrate that a two-step thermal treatment (100 °C then 150–300 °C) produces stationary phases with good properties for use in reversed-phase high-performance liquid chromatography.