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

Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO(2)) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120°C, 483 bar and 3 h reaction time, silica hydride (Si-H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si-H conversion efficiencies (as determined from (29)Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO(2) were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. (13)C and (29)Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO(2) was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO(2) presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach.     

Synthesis of chemically bonded cellulose trisphenylcarbamate chiral stationary phases for enantiomeric separation

Cellulose trisphenylcarbamate is regioselectively bonded to 3-aminopropyl silica gel and underivatized silica gel, respectively, at the 6-position of the primary hydroxyl group on the glucose unit of cellulose with 4,4'-diphenylmethane diisocyanate (DPDI) as a spacer. Enantioseparations are evaluated on these prepared chiral stationary phases (CSPs) with several organic acids as the modifiers in the mobile phase by high-performance liquid chromatography. The influence of the amount of DPDI used on chiral resolution is investigated. Also, the corresponding coated-type phase is also prepared for the aim of comparison. It is observed that the bonded-type phase shows a lower chiral recognition power but a better column efficiency than the coated-type phase under the liquid chromatographic mobile phase with hexane-alcohol. However, the bonded-type CSPs are compatible with a wider number of solvents such as tetrahydrofuran (THF) or chloroform, which generally result in the solubility or swelling of the cellulose derivatives on the coated-type CSPs. The results obtained from this study indicate that the bonded-type CSP may provide complementary enantioselectivity over the coated-type phase by adopting THF as a component in the mobile phase.     

The use of chemically bonded stationary phases in thin-layer chromatography-a survey

An overview is given of the literature publisned in the field of thin-layer chromatography on chemically bonded phases. Aspects which merit further attention are: quantitative analysis, organic solvent selection, stationary phase characteristics, surface modification of precoated silica plates, ion-pair chromatography and correlation of thin-layer and column chromatographic data.     

高效硅胶化学键合固定相的研究进展

对高效液相色谱用硅胶作为基质的化学键合固定相的研究进展进行了全面的评述。介绍了硅胶基质填料的物理化学性质及前处理过程,详细阐述了化学键合固定相的键合反应机制和种类,概括了化学键合固定相在高效液相色谱中的应用,并对我国的硅胶基质填料研究和应用前景进行了展望。     

Synthesis and characterization of new organometallic complexes bonded stationary phases for high-performance liquid chromatography

Summary The preparation, characterization and potential liquid chromatographic applications of various organometallic iron complexes silica stationary phases are presented. These new supports are synthesized by covalently linking ferrocene, as well as some of its cationic derivatives, to appropriately derivatized silica support matrices. These columns exhibit moderate to high selectivity towards the separation of polycyclic aromatic hydrocarbons (PAHs). A charge transfer retention mechanism has been proposed. A comparison with a reference stationary phase, 3,5-dinitrobenzamide (DNB), to quantify the acceptor power of the new stationary bonded phases, is also reported. Finally, the effect of varying the derivatives of the bonded metallocene on PAHs retention is discussed.     

Analysis of silica hydride and surface hydrosilation reactions by solid-state NMR in the preparation of<Emphasis Type="Italic"> p</Emphasis>-chlorobenzamide bonded silica phase

²⁹Si and ¹³C CP-MAS NMR spectroscopy was used to follow the conversion of native silica to a p-chlorobenzamide bonded silica material. The benzamide bonded phase was prepared via a hydrosilation reaction of a hydride silica intermediate with p-chloro-N-allylbenzamide. Solid-state NMR was used to show the disappearance of reactive surface hydride species (M_H) and to identify newly formed bonded chemical species on the silica surface. DRIFT spectroscopy, elemental analysis, and specific surface-area determinations (BET) of the prepared phases are also reported.     

Synthesis and evaluation of a C8 stationary phase on a silica hydride surface by hydrosilation of 1-octyne

The silanization/hydrosilation method is used to bond an alkyne (1-octyne) to a silica hydride surface. The new bonded material is characterized by elemental analysis and diffuse reflectance infrared Fourier transform spectroscopy. The hydrophobic behavior of this material was determined by the retention characteristics of aromatic solutes and the shape selectivity as well as phase classification (monomeric or polymeric) was measured by the polycyclic aromatic hydrocarbon mixture standard reference material 869. The presence of residual silanols on the bonded phase was probed by several basic solutes at pH 7. Long-term stability studies were conducted by measuring retention and peak symmetry of basic compounds over several thousand column volumes at pH 10.     

Effect of chemically bonded stationary phases and mobile phase composition on beta-blockers retention in RP-HPLC

The effects of stationary and mobile phase on retention of 18 beta-adrenolytic drugs (beta-blockers) have been studied. Four 'deactivated surface' stationary phases (polar-embedded or end-capped) were examined. Special attention was drawn to the cholesterolic (SG-CHOL) and alkylamide (SG-AP) stationary phases, and their application for analysis of the compounds. The retention of analyzed substances was also examined in terms of mobile phase composition. Sixteen different configurations of mobile phases were prepared, all based on methanol and acetonitrile with ammonium acetate and ammonium formate. The difference in retention between ammonium formate and acetate water solutions, and peak shape changes related to the addition of triethylamine (TEA), were investigated. Principal component analysis was used to find the similarities between stationary phases. Polar-embedded phases synthesized on the same sorbent possess very similar properties. All phases based on silica gel compared with the monolithic column also showed similarities in retention of beta-blockers. The addition of TEA to the mobile phase did not influence strongly the retention, and analysis of asymmetry factors showed only a little peak broadening for a few compounds on the monolithic column.     

Synthesis and characterization of a new type of chemically bonded liquid crystal stationary phase for HPLC

Summary Two commercially available liquid crystals, 4-cyano-4′-n-pentyl-1,1′-bipheny and 4-cyano-4′-n-pentoxy-1,1′-bipheny, are bonded to a silica hydride surface via hydrosilation in the presence of a free radical iniator, t-butyl peroxide. Elemental analysis, diffuse reflectance Fourier trans-form infrared spectroscopy, and¹³C and²⁹Si CP-MAS NMR spectroscopy are used to confirm the success of the bonding reaction. The¹³C CP-MAS spectra suggest a difference in the bonded phase morphology of the two materials. Static hydrolytic stability tests indicate these materials do not degrade significantly in both acidic and basic solutions. Chromatographic tests confirm that these two bonded phase behave differently with respect to their retention of PAHs, alkyl-substituted benzenes and benzodiazepines.     

Separation of lipid classes from plant tissues by high performance liquid chromatography on chemically bonded stationary phases

The wide range of lipid classes found in plant tissues, including simple lipids, glycolipids, and phospholipids, have been resolved by gradient high performance liquid chromatography with evaporative light-scattering detection. The lipids from potato tubers were used to optimize the separations. Adsorption chromatography with silica gel gave disappointing results for the plant glycolipids. Much better separations were obtained with chemically bonded stationary phases, e.g. those with propionitrile or polymeric vinyl alcohol as the functional moiety. With careful calibration, good reproducibility was possible. Only highly acidic lipids such as phosphatidylserine still present some problems.     

New alumina-based stationary phases for high-performance liquid chromatography Synthesis by olefin hydrosilation on a silicon hydride-modified alumina intermediate

A silanization procedure is used to form a layer of silicon hydride on the surface of alumina. IR and NMR data confirm the presence of the hydride on the surface. Modification of the hydride intermediate is accomplished by reaction with a terminal olefin in the presence of a transition metal catalyst to form an alkyl-bonded material. Both IR and NMR confirm the bonding of the alkyl ligand to the hydride surface. Chromatographic tests indicate reversed-phase behavior. Exposure to high concentrations of phosphate solution for an extended period resulted in no significant deterioration of the bonded phase.     

Evaluation of the dual retention properties of stationary phases based on silica hydride: Perfluorinated bonded material

The synthesis of a new perfluorinated stationary phase based on silica hydride using a hydrosilation reaction was investigated. The material was characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy and ¹³C cross‐polarization magic‐angle spinning NMR spectroscopy. The retention properties of this new material were tested in the reversed‐phase and normal‐phase mode. Variable buffer strength experiments at two pH conditions for selected polar compounds were used to compare the new phase to hydrophilic interaction liquid chromatography retention. These results and previous data reported in the literature were used to postulate differences in the retention mechanism between hydrophilic interaction liquid chromatography and silica hydride‐based stationary phases.     

Influence of mobile phase composition on retention factors in different HPLC systems with chemically bonded stationary phases

The influence of mobile phase composition on the retention of selected test analytes in different normal- and reversed-phase chromatographic systems is studied. A novel adsorption model for an accurate prediction of the analyte retention in the column chromatography with binary mobile phase is proposed. Performance of the model is compared with the retention model reported in the literature. Both models are verified for different HPLC systems by use of three criteria: (a). the sum of squared differences between the experimental and theoretical data, (b). approximation of the standard deviation, and (c). the Fisher test.     

Structure-function relationships in high-density docosylsilane bonded stationary phases by Raman spectroscopy and comparison to octadecylsilane bonded stationary phases: effects of aromatic compounds

The effects of four aromatic compounds on alkyl chain conformational order for a series of high-density docosylsilane (C22) stationary phases with surface coverage ranging from 3.61 to 6.97 micromol/m2 are investigated using Raman spectroscopy. Aromatic compounds studied include benzene-d6, toluene-d8, aniline-d7 and anisole-d8. In general, these aromatic solvents decrease the conformational order of the C22 phases relative to air suggesting partitioning of the aromatics into the alkyl chains of these stationary phases. Changes in alkyl chain conformational order are linearly dependent on the solvent hydrophobicity parameter, log K ow, and are also dependent on stationary phase properties (i.e. polymerization method and surface coverage). A comparison is made between C22 and C18 bonded phase systems. The conformational order of the alkyl chains in a mixed solute/mobile phase system is also studied using 80% methanol/water as the mobile phase and aniline-d7, anisole-d8 or toluene-d8 as solutes. Collectively, the Raman spectroscopic evidence at the molecular level suggests interaction of these aromatic species with the bonded alkyl chains through partitioning.     

Thin-layer chromatography of metal ions on bonded stationary phases

Summary The separation of iron, copper, nickel, and zinc by thin-layer chromatography was studied. Eight bonded-phase silica substrates and twenty-nine solvent systems were investigated. Solutions of 1% diphenylcarbazide in ethanol and 1% K₄Fe(CN)₆ in water were used to detect the metal ions. The best separation was obtained with an immobilized trifluoroacetylacetone substrate and 10% trifluoroacetylacetone in acetone mobile phase.