Mercaptopropyl functionalized polymethylsilsesquioxane microspheres have been prepared by a two-step acid/base catalyzed hydrolysis and co-condensation of methyltrimethoxysilane (MTMS) and mercaptopropyltrimethoxysilane (MpTMS) precursors. The mercaptopropyl loading of the microspheres is controlled by regulating the ratio of MpTMS to MTMS in the reaction feedstock. A pronounced decrease in surface area, pore volume, and pore size with increasing mercaptopropyl loading was observed and a transition in pore structure from mesopores to micropores/nearly nonporous occurred at mole fractions of mercaptopropyl groups greater than 0.23. The resulting particles exhibited low silanol/thiol activity as both the concentrations and dissociation constants of the acidic groups were considerably lower than those reported for inorganic silica-based packings. Chromatographic evaluation using a test mixture containing uracil, toluene, ethylbenzene, quinizarin, and amitriptyline revealed that the new materials possess typical reverse phase chromatographic properties with moderate methylene selectivity and intrinsic inertness to bases. Taken together, the mercaptopropyl functionalized microspheres are a promising alternative to base-deactivated silica-based packings for the separation of the basic compounds which constitute a large proportion of pharmaceuticals.

•A method for separation and identification of oligomeric phenylethoxysiloxanols is described.•The method can be used to monitor the distribution of oligomers and the structure growth in the sol–gel process.•The oligomer species evolve from linear to cyclic structures with increasing amount of water in the reaction mixture.•The phenyl and ethoxy moieties in the oligomer molecule are responsible for solute retention in reversed-phase systems.Liquid chromatography-electrospray ionization mass spectrometry has been applied to qualitative analysis of oligomeric phenylethoxysiloxanols, a class of organosilanols as active intermediates to polyhedral silsesquioxanes. The phenylethoxysiloxanol samples were prepared by controlled acid-catalyzed hydrolysis and condensation of phenyltriethoxysilane at various molar equivalents of water (r1) and characterized by standard spectroscopic techniques. Using a gradient binary water–methanol mobile phase, these reaction products were resolved on octadecylsiloxane silica stationary phase and subsequently identified by online electrospray ionization mass spectrometric detection. Results show that the reaction products are composed of a multitude of linear and monocyclic siloxanol oligomers with various numbers of silicon atoms and hydroxyl groups, depending upon the reaction conditions used. With the r1 value increasing from 0.5 to 2.0, the chain lengths of the oligomers increase slightly but the numbers of hydroxyl groups increase considerably, accompanying by structural evolution from chains to rings. Characterization of the retention behavior of these oligomers indicates that hydrophobic interactions of phenyl and ethoxy groups with the stationary phase are responsible for their retention in reversed-phase liquid chromatography.

•A method for separation and identification of oligomeric vinylmethoxysiloxanes prepared under different conditions is described.•Linear or cyclic oligomers with silicon atoms ranging from 3 to 11 are the predominant species depending upon the reaction conditions.•The oligomers evolve from linear to mono- and bicyclic structures with increasing amount of water in the reaction mixture.•The method can be used to determine the molar mass distribution parameters for oligomers for which no molar mass standards are available.A high-performance liquid chromatography with online electrospray ionization mass spectrometry (HPLC–ESI-MS) has been used to separate and identify the reaction products resulting from controlled acid-catalyzed hydrolytic polycondensation of vinyltrimethoxysilane (VMS). The reaction products were prepared in the molar ratio of water to VMS (r1) ranging from 0.6 to 1.2, characterized by standard spectroscopic techniques, and subsequently analyzed by HPLC–UV absorbance detection and HPLC–ESI-MS. Linear vinylmethoxysiloxane oligomers with the number of repeat units (n) ranging from 3 to 11 are predominant species at the beginning of the reaction (for r1 = 0.6). Then they transform into monocyclic (for r1 = 1.0) and bicyclic (for r1 = 1.2) species with gradually increasing amount of water in the reaction mixture. The oligomer conversions suggest that structure growth of vinylmetoxysiloxanes proceeds by nonrandom cyclization reactions, which are favored over chain extension under the chosen reaction conditions. Direct ESI-MS, HPLC–ESI-MS and HPLC–UV were used to determine the molar mass distributions for the vinylmethoxysiloxane oligomers prepared in three different values of r1. The molar mass averages increase slightly with the amount of water in the reaction mixture and vary somewhat with the method used. Our results indicate that with the combined capability of separation, sensitivity and identification, HPLC–ESI-MS is especially useful to study highly complex silicon-based compounds with hyperbranched, caged or cubic structures as building blocks for hybrid materials.

•Gradient elution chromatography for separation of a light stabilizer Chimassorb 944 into individual oligomers is presented.•The oligomers are identified by fluorescent derivatization and matrix-assisted laser desorption/ionization mass spectrometry.•Chimassorb 944 is shown to consist of a series of dominant linear oligomers together with minor cyclic species.•The HPLC method can be used to determine the molar mass distribution of Chimassorb 944.A non-aqueous reversed-phase high-performance liquid chromatographic (HPLC) method has been developed to separate a light stabilizer Chimassorb 944 into individual oligomers, which are further identified using pre-column fluorescent derivatization and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Consistent with previous studies, we find that the Chimassorb 944 product is a complex mixture consisting of a homologous series with the amine end groups and the number of repeat units (n) span from 1 to 26. In addition to the dominant linear species, cyclic oligomers are present at relatively high levels in the low-mass range. Their concentration decreases rapidly with the length of the oligomer backbone and becomes undetectable when n > 7. Moreover, comparison of the HPLC and MALDI-MS molar mass distributions of Chimassorb 944 shows that the HPLC analysis produces greater molar mass averages and thus offers an effective means for accurate measure of the relative abundances of the oligomers.

Although magnetic field-flow fractionation (MgFFF) is emerging as a promising technique for characterizing magnetic particles, it still suffers from limitations such as low separation efficiency due to irreversible adsorption of magnetic particles on separation channel. Here we report a novel approach based on the use of a cyclic magnetic field to overcome the particle entrapment in MgFFF. This cyclic field is generated by rotating a magnet on the top of the spiral separation channel so that magnetic and opposing gravitational forces alternately act on the magnetic particles suspended in the fluid flow. As a result, the particles migrate transversely between the channel walls and their adsorption at internal channel surface is prevented due to short residence time which is controlled by the rotation frequency. With recycling of the catch-release process, the particles follow saw-tooth-like downstream migration trajectories and exit the separation channel at velocities corresponding to their sedimentation coefficients. A retention model has been developed on the basis of the combined effects of magnetic, gravitational fields and hydrodynamic flow on particle migration. Two types of core–shell structured magnetic microspheres with diameters of 6.04- and 9.40-μm were synthesized and used as standard particles to test the proposed retention theory under varying conditions. The retention ratios of these two types of particles were measured as a function of magnet rotation frequency, the gap between the magnet and separation channel, carrier flow rate, and sample loading. The data obtained confirm that optimum separation of magnetic particles with improved separation efficiency can be achieved by tuning rotation frequency, magnetic field gradient, and carrier flow rate. In view of the widespread applications of magnetic microspheres in separation of biological molecules, virus, and cells, this new method might be extended to separate magnetically labeled proteins or organisms for multiplex analyte identification and purification.

Solid-phase extraction has been widely employed for the preparation of DNA templates for polymerase chain reaction (PCR)-based analytical methods. Among the variety of adsorbents studied, magnetically responsive silica particles are particularly attractive due to their potential to simplify, expedite, and automate the extraction process. Here we report a facile method for the preparation of such magnetic particles, which entails impregnation of porous silica microspheres with iron salts, followed by calcination and reduction treatments. The samples were characterized using powder X-ray diffractometry (XRD), scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherms, and vibrating sample magnetometry (VSM). XRD data show that magnetite nanocrystals of about 27.2 nm are produced within the pore channels of the silica support after reduction. SEM images show that the as-synthesized particles exhibit spherical shape and uniform particle size of about 3 μm as determined by the silica support. Nitrogen sorption data confirm that the magnetite-loaded silica particles possess typical mesopore structure with BET surface area of about 183 m2/g. VSM data show that the particles display paramagnetic behavior with saturation magnetization of 11.37 emu/g. The magnetic silica microspheres coated with silica shells were tested as adsorbents for rapid extraction of genomic DNA from soybean-derived products. The purified DNA templates were amplified by PCR for screening of genetically modified organisms (GMOs). The preliminary results confirm that the DNA extraction protocols using magnetite-loaded silica microspheres are capable of producing DNA templates which are inhibitor-free and ready for downstream analysis.

Fabrication of porous frits to retain stationary phases is a critical issue in column preparation for capillary electrochromatography (CEC). In this work, porous frits were prepared by applying an external magnetic field to magnetically responsive particles placed inside a fused-silica capillary. Three batches of uniform magnetite spheres with particle diameters of 0.3, 0.4, and 0.6 μm and saturation magnetization values of 73.03, 74.41, and 77.83 emu/g, respectively, were used as frit particles and octadecyl- and phenyl-bonded silica gels were packed successfully into frit-containing capillaries. The performance of the resulting magnetically immobilized frits and packed columns was evaluated. The electroosmotic mobilities in capillaries containing outlet frit only were found to be reduced by 2–4% whereas the plate heights of an unretained marker increased by 30–50% as compared to those in open capillaries. These variations are believed to be associated with the inhomogeneities of the packed structure of the frits. The magnetically immobilized frits showed adequate mechanical strength to withstand the flow drag force, allowing separation in capillaries packed with 5-μm stationary phases up to 10–15 cm, thus rendering column efficiency and reproducibility comparable with those obtained with sintered frits. Taken together, retaining frits made of uniform magnetite particles serves as a viable alternative to sintered frits for column preparation, which offers several distinct advantages such as ease of preparation, improved durability as compared to sintered frits where the removal of the polyimide coating makes the packed column susceptible to breakage, and use of large-bore capillaries for semipreparative separations.