The structural and chromatographic characteriza- tion of two novel fluorinated mesoporous materials pre- pared by covalent reaction of 3-(pentafluorophenyl)propyldi- methylchlorosilane and perfluorohexylethyltrichlorosilane with 2.5 mm fully porous silica particles is reported. The ad- sorbents were characterized by solid state 29Si, 13C, and 19 F NMR spectroscopy, low-temperature nitrogen adsorption, elemental analysis (C and F), and various chromatographic measurements, including the determination of adsorption isotherms. The structure and abundance of the different or- ganic surface species, as well as the different silanol types, were determined. In particular, the degree of so-called hori- zontal polymerization, that is, Si-O-Si bridging parallel to the silica surface due to the reaction, under “quasi-dry” conditions, of trifunctional silanizing agents with the silica surface was quantified. Significant agreement was found between the information provided by solid-state NMR, elemental analysis, and excess isotherms regarding the amount of sur- face residual silanol groups, on the one hand, and the degree of surface functionalization, on the other. Finally, the kinetic performance of the fluorinated materials as separa- tion media for applications in near-ultrahigh-performance liquid chromatography was evaluated. At reduced velocities of about 5.5 (ca. 600 bar backpressure at room temperature) with 3 mm diameter columns and toluene as test com- pound, reduced plate heights on the order of 2 were ob- tained on columns of both adsorbents.
Revealing the fine details of functionalized silica surfaces by solid-state NMR and adsorption isotherm measurements: the case of fluorinated stationary phases for liquid chromatography
MARCHETTI, Nicola;PASTI, Luisa;MASSI, Alessandro;CAVAZZINI, Alberto
2014
Abstract
The structural and chromatographic characteriza- tion of two novel fluorinated mesoporous materials pre- pared by covalent reaction of 3-(pentafluorophenyl)propyldi- methylchlorosilane and perfluorohexylethyltrichlorosilane with 2.5 mm fully porous silica particles is reported. The ad- sorbents were characterized by solid state 29Si, 13C, and 19 F NMR spectroscopy, low-temperature nitrogen adsorption, elemental analysis (C and F), and various chromatographic measurements, including the determination of adsorption isotherms. The structure and abundance of the different or- ganic surface species, as well as the different silanol types, were determined. In particular, the degree of so-called hori- zontal polymerization, that is, Si-O-Si bridging parallel to the silica surface due to the reaction, under “quasi-dry” conditions, of trifunctional silanizing agents with the silica surface was quantified. Significant agreement was found between the information provided by solid-state NMR, elemental analysis, and excess isotherms regarding the amount of sur- face residual silanol groups, on the one hand, and the degree of surface functionalization, on the other. Finally, the kinetic performance of the fluorinated materials as separa- tion media for applications in near-ultrahigh-performance liquid chromatography was evaluated. At reduced velocities of about 5.5 (ca. 600 bar backpressure at room temperature) with 3 mm diameter columns and toluene as test com- pound, reduced plate heights on the order of 2 were ob- tained on columns of both adsorbents.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
