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.

A Silica‐Supported Catalyst Containing 9‐Amino‐9‐deoxy‐9‐epi‐quinine and a Benzoic Acid Derivative for Stereoselective Batch and Flow Heterogeneous Reactions

“…In fact, mesoporous and nonporous silica offer high surface area, mechanical stability, robustness and an easy surface multi‐steps modification of silanols with organosilanes. Even a control of surface modification results facilitated with solid‐state 13 C and 29 Si NMR experiments …”

Effect of Natural Deep Eutectic Solvents on trans-Resveratrol Photo-Chemical Induced Isomerization and 2,4,6-Trihydroxyphenanthrene Electro-Cyclic Formation

“…UPLC-DAD/MS was performed on a Waters Acquity H-Class UPLC system (Waters, Milford, MA, USA), including a quaternary solvent manager (QSM), a sample manager with a flow through needle system (FTN), a photodiode array detector (PDA) and a single-quadruple mass detector with electrospray ionization source (ACQUITY QDa). Chromatographic analyses were performed on a non-commercial pentafluorophenyl column (75 mm × 3.2 mm i.d., 2.5 μm particle size) developed and prepared by Ciogli and co-workers [ 34 ]. The mobile phase was composed by solvent A, 0.1% aqueous HCOOH, and solvent B as 0.1% HCOOH in CH 3 CN.…”

Effects of Residual Silanol on Solid Phase Extraction of Organic Compounds to Octadecylsilyl Silica

“…Silanol, however, does exist in such EC-ODS silica. It is recommended that the contribution of silanol to retention in RPLC both as the hydrogen-bond donor and acceptor, and the properties characterized by spectroscopy such as IR and CP/MAS 29 Si NMR 3,6,7 be taken into account. 8 Accompanied with an increased surface density of alkyl groups on silica gel, reduction in retention or reduction in reproducibility of the retention time of RPLC became noticed in the use of a highly aqueous mobile phase; this was attributed to dewetting of or formation of a gas phase in micropores.…”