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 |
| |
Authors: | Dr Alessia Ciogli Dr Patrizia Simone Prof Claudio Villani Prof Francesco Gasparrini Prof Aldo Laganà Dr Donatella Capitani Dr Nicola Marchetti Dr Luisa Pasti Dr Alessandro Massi Dr Alberto Cavazzini |
| |
Institution: | 1. Dipartimento di Chimica e Tecnologia del Farmaco, University “La Sapienza”, Rome (Italy), Fax: (+39)?06‐49912780;2. University of Rome, “La Sapienza”, Department of Chemistry, Piazzale Aldo Moro 5, 00185 Rome (Italy);3. Consiglio Nazionale delle Ricerche CNR, Istituto di Metodologie Chimiche, Via Salaria Km 29,300 C.P.10, 00016 Monterotondo Stazione, Rome (Italy);4. University of Ferrara, Department of Chemistry and Pharmaceutical Sciences via L. Borsari, 46, 44121 Ferrara (Italy), Fax: (+39)?0532‐24070 |
| |
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 29Si, 13C, and 19F 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. |
| |
Keywords: | adsorption liquid chromatography NMR spectroscopy silica surface chemistry |
|
|