title: 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.
abstract: The structural and chromatographic characterization of two novel fluorinated mesoporous materials prepared by covalent reaction of 3-(pentafluorophenyl)propyldimethylchlorosilane and perfluorohexylethyltrichlorosilane with 2.5 μm fully porous silica particles is reported. The adsorbents were characterized by solid state (29)Si, (13)C, 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 organic surface species, as well as the different silanol types, were determined. In particular, the degree of so-called horizontal 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 surface 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 separation 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 compound, reduced plate heights on the order of 2 were obtained on columns of both adsorbents.
authors.affiliation: Dipartimento di Chimica e Tecnologia del Farmaco, University "La Sapienza", Rome (Italy), Fax: (+39) 06-49912780.
authors.forename: Alessia
authors.initials: A
authors.lastname: Ciogli
authors.forename: Patrizia
authors.initials: P
authors.lastname: Simone
authors.forename: Claudio
authors.initials: C
authors.lastname: Villani
authors.forename: Francesco
authors.initials: F
authors.lastname: Gasparrini
authors.forename: Aldo
authors.initials: A
authors.lastname: Laganà
authors.forename: Donatella
authors.initials: D
authors.lastname: Capitani
authors.forename: Nicola
authors.initials: N
authors.lastname: Marchetti
authors.forename: Luisa
authors.initials: L
authors.lastname: Pasti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Massi
authors.forename: Alberto
authors.initials: A
authors.lastname: Cavazzini
mesh_terms: D000327:Adsorption; D002853:Chromatography, Liquid / Q000379:methods*; D054879:Halogenation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D012822:Silicon Dioxide
keywords: NMR spectroscopy; adsorption; liquid chromatography; silica; surface chemistry