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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., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Endcapped stationary phases were prepared after thermal immobilization of poly(methyloctadecylsiloxane) (PMODS) onto zirconized and titanized silica supports. These new stationary phases have lower densities of residual hydroxyl groups, according to infrared spectroscopy and 29Si CP-MAS NMR and as shown by the symmetrical peaks of basic compounds from the Tanaka, Engelhardt and SRM 870 test mixtures. Stability tests for the endcapped stationary phases, measured using severe alkaline conditions (70:30 (v/v) methanol:0.05 mol/L K2CO3/KHCO3, pH 10, 50 °C), revealed that the stabilities of these phases are greater than the stabilities of similar nonendcapped phases. The stationary phases showed good performance for the separation of basic pharmaceuticals., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This study describes the preparation and characterization of a HPLC stationary phase (SP) obtained by deposition of poly(methyloctadecylsiloxane) (PMODS) onto the surface of porous zirconized silica particles, followed by thermal immobilization. The SP were characterized using elemental analysis and infrared and (29)Si NMR spectroscopies, while their chromatographic behaviors were investigated by separation of selected neutral, acidic and basic compounds of different test mixtures (Engelhardt, SRM 870 and Tanaka tests). The preparation of the metalized support and the thermal immobilization of PMODS onto zirconized silica, optimized by experimental design, produced a SP based on PMODS that showed high values of efficiency (up to 85000 plates/m) and appropriate asymmetry factors. The presence of zirconium on the surface significantly decreases silica solubility in severe conditions (alkaline mobile phase at pH 10 and high temperature), increasing column lifetime., (Copyright © 2011 Elsevier B.V. All rights reserved.)