Characterization of stationary phases based on polysiloxanes thermally immobilized onto silica and metalized silica...

Stationary phases (SP) prepared by immobilization of polymers on silica or metalized silica are interesting for use in reversed-phase high-performance liquid chromatography (RP-HPLC) due to better protection of residual silanols or Lewis acid sites, as well as ease of preparation. On the other hand, there are no previous reports of the use of such phases in packed column supercritical fluid chromatography (SFC). Fourteen different SPs based on polysiloxanes (phenyl, C1, C8, C14, C18) thermally immobilized onto different supports (silica, titanized silica, zirconized silica) and one chemically bonded and end-capped C18 stationary phase having a doubly zirconized silica support, were characterized with identical SFC conditions (CO2 with 10% of methanol, 25°C, 15.0 MPa backpressure). Characterization was achieved based on retention factors measured for 85 test compounds and linear solvation energy relationships (LSER), namely the solvation parameter model based on Abraham descriptors. The polysiloxane SP were compared to a commercial C18-bonded silica (Kromasil C18), and to the native silica and metalized silica supports to better unravel the effects of stationary phase chemistry on chromatographic behavior. Together, 19 stationary phases were compared. The results highlight the variety of polarities provided by the column set. The polysiloxane backbone contributes significantly to the SP polarity as evidenced by the comparison to a classical alkylsiloxane-bonded SP. Metalization also appears to modify the polar characteristics of the SP, particularly toward basic compounds. Sample applications illustrate the applicability of these SP in SFC to the analysis of compounds of interest to the pharmaceutical and cosmetic industries.