New Approaches to Prepare Hydride Silica

Abstract

Two synthetic schemes to produce a hydride-modified support that serves as an intermediate for the preparation of bonded phases for liquid chromatography (LC) and capillary electrophoresis (CE) are investigated. The strategies differ in the silane reagent utilized (trichlorosilane (TCS) or triethoxysilane (TES)) and the manner water is incorporated into the reaction. In the first approach, TCS in toluene reacts with a previously humidified silica substrate so that the reaction is confined to the silica surface. In the second approach, TES and a small amount of aqueous HCl are dissolved in THF, and this hydrolysate is diluted by a great factor in cyclohexane, prior to reaction with the silica substrate. Atomic force microscopy (AFM) images of the hydride film on wafers revealed that, unlike the traditional approach that produced a patchy coating, both new methods provided a homogeneous layer on the substrate's surface. IR and NMR spectra from porous silica particles clearly confirmed a successful surface modification. AFM and water contact angles (WCA) were used to examine the effect of dilution of the TES hydrolysate in cyclohexane on the trend of the film to polymerize on wafers and found that a dilution factor of at least 100 is required to attain a molecularly thin hydride layer. WCA and CE also revealed a strong susceptibility of the hydride silica intermediate to hydrolyze, even at low pH. Compared to TCS, the lower reactivity and volatility of TES resulted in a much more desirable experimental approach.

Neutral hydrophilic coatings for capillary electrophoresis prepared by controlled radical polymerization

“…To further characterize the polymeric film on the silica surface, AFM was used on coated silica plates by probing the surface after polymerization. As shown in Figure 3, the surface is uniformly coated with the polymeric film and exhibits a more rugose surface topography (rugosity = 3.16 nm), in comparison to an unmodified plate (~ 0.3 nm)(28). Thickness measurements with ellipsometry revealed a uniform film with a layer thickness of 53 ± 2 nm.…”

“…Porous silica particles did not undergo any conditioning. Hydride silica substrates were prepared as described previously (28). 3-hydroxypropyl (propanol) bonded silica phase was prepared by hydrosilylation of allyl alcohol on hydride silica, as described in a recent report (29).…”

“…DRIFT, solid state NMR and AFM measurements were obtained accordingly to previously described procedures (28). An Uvisel 2 Spectroscopic Phase Modulated ellipsometer was used for film thickness measurements at Horiba Scientific laboratories (France).…”

Prediction of the zeta potentials and ionic descriptors of a silica hydride stationary phase with mobile phases of different pH and ionic strength

“…Overthelastdecade,silicahydridestationaryphases,with$95%of the surface silanols replaced by Si-H groups, have been developed [1,2]. Further modification of the silica hydride surface, e.g., through a hydrosilation reaction, can also be achieved, offering ligand-bonded stationary phases with different selectivities depending on the chemical nature of the organic moiety used [3][4][5].…”

Silica hydride intermediate for octadecylsilica and phenyl bonded phase preparation via heterogeneous hydrosilation in supercritical carbon dioxide

“…The unique properties of silica hydride and its bonded phases in a variety of chromatographic applications and formats have been recently reviewed [19]. New approaches to the preparation of silica hydride continue to be of interest [25], including an effective hightemperature chlorination-reduction sequence for the preparation of silicon hydride modified silica surfaces which has also recently been reported [26].…”