Improved chemical stabilities for end-capped high performance liquid chromatography stationary phases based on poly(methyloctadecylsiloxane) thermally immobilized onto metalized silicas

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.

► HPLC support prepared by metallization of silica and thermal immobilization of PMODS onto the support.
► Endcapping reaction with hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS).
► Evaluation with several standardized test mixtures.
► Improvement of the chemical stability in severe alkaline conditions.
► Potential application for separation of basic pharmaceuticals.