Polymer encapsulated packing material for reversed phase liquid chromatography

Facile Synthesis and Chiral Separation of Chiral Mesoporous Silica Microspheres

Mesoporous silica microspheres were synthesized by an acid-catalyzed sol-gel method using tetraethoxysilane (TEOS) as a precursor. The hydrochloric acid was used as a catalyzer to induce the hydrolysis of TEOS, while the cyclohexane acted as a stabilizer of the sol. The addition of polyethylene glycol can introduce the uniform mesoporous structure into the microspheres by phase separation. The as-prepared mesoporous silica microspheres possess a narrow particle size distribution, a mesopore size of 5.0 nm and a Brunauer-Emmett-Teller specific surface area as high as 230 m2·g-1. The resultant silica microspheres were used for packing chiral high-performance liquid chromatography (HPLC) columns, after activated by hydrochloric acid and modified by amylose-tris(3,5-dimethylphenylcarbamate), respectively. The flurbiprofen axetil as a typical chiral drug with two stereocenters can be successfully separated by the as-obtained chiral HPLC columns using different mobile phases.

Kinetics and Isotherm for Adsorption of Hg(II) from Aqueous Solution by Silica Gel Encapsulated by Polyamine-Functionalised Polystyrene

This paper presents the synthesis of two novel composite adsorbents, namely (i) silica gel microspheres encapsulated with diethylenetriamine-functionalised polystyrene (SG – PS – SO2 – DETA) and (ii) silica gel microspheres encapsulated with triethylenetetramine-functionalised polystyrene (SG – PS – SO2 – TETA). Our objective was to design adsorbents with high adsorption capacities via different functional groups, and the results showed that SG – PS – SO2 – TETA has an excellent adsorption capacity for Hg(II) ions. A kinetic investigation of SG – PS – SO2 – DETA and SG – PS – SO2 – TETA for adsorption of Hg(II) is reported here and the results show that SG – PS – SO2 – DETA/SG – PS – SO2 – TETA could attain their saturation adsorption capacities within 4 h, and their excellent adsorption capacities for Hg(II) were 0.252 mmol g −1 and 0.383 mmol g −1, respectively. Moreover, the kinetic data indicated that the adsorption process is governed by the film diffusion. Langmuir and Freundlich isotherm models were applied to analyse the experimental data and the maximum adsorption capacities of SG – PS – SO2 – DETA and SG – PS – SO2 – TETA for Hg(II) were 46.54 mg g −1 and 113.47 mg g −1, respectively.

Synthesis and characterization of silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene and its adsorption of transition metal ions from aqueous solutions

The present study was undertaken to develop a novel adsorbent for heavy metal ions, and this paper presents the synthesis and characterization of a composite material-silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) with a core-shell structure. SG-PS-azo-SA was used to investigate the adsorption of Mn(II), Co(II), Ni(II), Fe(III), Hg(II), Zn(II), Cd(II), Cr(VI), Pd(II), Cu(II), Ag(I), and Au(III) from aqueous solutions. The results revealed that SG-PS-azo-SA has better adsorption capacity for Cu(II), Ag(I) and Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation with the maximum adsorption capacity for Cu(II), Ag(I), and Au(III) at 1.288 mmol g−1, 1.850 mmol g−1 and 1.613 mmol gt-1, respectively. Thus, silica gel encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) is favorable and useful for the removal of Cu(II), Ag(I) and Au(III) metal ions.

Removal of transition metal ions from aqueous solutions by adsorption onto a novel silica gel matrix composite adsorbent

This paper presented the synthesis of a novel composite adsorbent silica gel microspheres encapsulated with 5-sulfosalicylic acid functionalized polystyrene (SG-PS-azo-SSA). It was characterized by titration method, FT-IR (Fourier transform infrared spectrometer), SEM (scanning electron microscope), EDXAS (energy dispersive X-ray analysis system), etc. SG-PS-azo-SSA has been used to investigate the adsorption of Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Pd(II), Cu(II), Ag(I) and Au(III) from aqueous solutions. The research results revealed that SG-PS-azo-SSA has the better adsorption capacity for Cu(II), Ag(I) and Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data and the adsorption of Cu(II), Ag(I) and Au(III) on SG-PS-azo-SSA fitted well to the Langmuir isotherm equation. The obtained maximum adsorption capacity for Cu(II), Ag(I), and Au(III) is 0.472 mmol/g, 0.822 mmol/g and 0.810 mmol/g, respectively. Thus, silica gel encapsulated by 5-sulfosalicyclic acid functionalized polystyrene (SG-PS-azo-SSA) is favorable and useful for the removal of Cu(II), Ag(I) and Au(III) metal ions.

Quantitative structure-retention relationships of benzoylphenylureas on polystyrene-octadecene-encapsulated zirconia stationary phase in reversed-phase high performance liquid chromatography

Quantitative Structure-Retention Relationships of benzoylphenylureas and similar compounds have been studied on a new type of stationary phase (polystyrene-octadecene-encapsulated zirconia) in reversed-phase high performance liquid chromatography. Using stepwise regression analysis, the relationships between the structural descriptors of the compound and its chromatographic retention were examined. It was confirmed that the retention of the dihalogenobenzoylphenylureas is mainly governed by the dipole moment (DM), the calculated molar refractivity (CMR), and the hydrophobicity parameter (C log P) of the compounds. The predicting equations for the 18 dihalogenobenzoylphenylureas and similar compounds were also established; there is a good agreement between the observed k values and the predicted k values. In addition, a typical ODS (Kromasil-C18-SiO2) was compared with C18-PS-ZrO2. The results showed that there were some differences between the two stationary phase for the separation of the compounds investigated, which are certainly related to surface characteristics of the two different supports.

Titanized silica-based stationary phases prepared with thermally and microwave-immobilized poly(methyloctylsiloxane)

Silica supports having their surface modified with titanium oxide were prepared and coated with poly(methyloctylsiloxane) (PMOS). Subsequently, immobilization of the polysiloxane was induced by thermal treatment or microwave radiation. The thermal treatment was carried out for different times (4, 8, 16 and 24 h) at temperatures ranging between 100 and 220 degrees C. For PMOS immobilization by microwave radiation, 452, 520 and 586 W power levels and exposure times of 5, 15 and 30 min were used. After extraction of non-immobilized polymer, the chromatographic properties of the phases were evaluated. The phase immobilized at 120 degrees C for 8 h presented the best chromatographic parameters, suggesting that the quantity of acidic hydroxyl groups on the support surface was reduced, resulting in fewer undesirable interactions of a basic solute with the silanols not removed or covered on the support surface.

Part II. Chromatography using ultra-stable metal oxide-based stationary phases for HPLC

In this part of the review authors discuss methods used for modification of metal oxide surfaces. On the basis of literature data it is shown, that silanization of the surfaces do not form stable supports for chromatography. On the other hand, the success of polymer modified surfaces such as polybutadiene (PBD) and polystyrene (PS) is emphasized. Permanent modification of metal oxide surfaces with Lewis bases is also widely discussed. Chromatographic properties of polymer modified surfaces of zirconia are discussed in details. The perspectives of carbon-coated metal oxide surfaces in HPLC and high temperature separations are described.

Studies on a poly(styrene-divinylbenzene)-encapsulated sub-micrometer sized organic–inorganic hybrid silica packing, its synthesis, some of its characteristics and applications

The hydrolyzed product of a mixture of tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTEOS) was used to produce organic-inorganic hybrid silica by sol-gel processing. The product was a kind of composite with vinyl groups incorporated into the structure of the final particles through C-Si bonds. These hybrid silica particles were spherical and the average diameter was about 350 nm as measured by scanning electron microscopy (SEM). The particles were non-porous as proved by BET method. The hybrid silica particles were subsequently encapsulated with a layer of PS-DVB, a polymeric mixture of styrene and divinylbenzene, with the vinyl groups on the particle surface as anchors of the polymer chains. The encapsulated packing was used as stationary phases in CEC, and the chromatographic behaviors were studied. Experimental results showed that, as expected, the smaller diameter stationary phase resulted in higher column efficiencies. In comparison with the columns packed with 5 microm diameter encapsulated-silica stationary phases of the same kind and other sub-micron stationary phases reported, it can be concluded that the EOF velocity is independent of the particle diameter when using 350 nm phase, but determined by the surface nature of the stationary phase.

New synthetic ways for the preparation of high-performance liquid chromatography supports

The latest developments and in particular important synthetic aspects for the preparation of modern HPLC supports are reviewed. In this context, the chemistry of inorganic supports based on silica, zirconia, titania or aluminum oxide as well as of organic supports based on poly(styrene-divinylbenzene), acrylates, methacrylates and other, more specialized polymers is covered. Special consideration is given to modern approaches such as sol-gel technology, molecular imprinting, perfusion chromatography, the preparation of monolithic separation media as well as to organic HPLC supports prepared by new polymer technologies such as ring-opening metathesis polymerization. Synthetic particularities relevant for the corresponding applications are outlined.

Chromatographic behavior of poly(styrene-divinybenzene) encapsulated packing material for capillary electrochromatography

Poly(styrene-divinylbenzene) encapsulated silica (PS-DES) was synthesized and its characteristics as capillary electrochromatography stationary phase were studied. On capillary columns packed with this stationary phase, the effects of acetonitrile concentration as well as pH values on electroosmotic flow, and the effect of the latter on column efficiency were evaluated. Aromatic hydrocarbons, polar and basic medicinal compounds were successfully separated by using reversed-phase elution. It was evident that selectivity based on pi-pi electronic interaction between solute and stationary phase molecules contributed to the separation. Peaks in the chromatograms obtained were generally symmetrical. At a pH of the mobile phase as high as 11.2, the stationary phase was still stable after more than 160 h of exposure.

Influences of surface chemistry on the separation behavior of stationary phases for reversed-phase and ion-exchange chromatography: a comparison of coated and grafted supports prepared by ring-opening metathesis polymerization

A series of poly(norborn-2-ene) (poly-NBE), poly(7-oxanorborne-2-ene-5,6-dicarboxylic acid) (poly-ONDCA), as well as poly(norborn-2-ene-co-7-oxanorborne-2-ene-5,6-dicarboxylic acid) (poly-NBE-co-ONDCA) based silica supports were prepared via ring-opening metathesis polymerization (ROMP) using both coating and grafting techniques. Poly-NBE-grafted and poly-NBE-coated supports were used for the reversed-phase separation of phenols; poly-NBE, poly-ONDCA as well as poly-NBE-co-ONDCA-grafted supports were used for comparative studies on the separation of a series of anilines and lutidines. As expected, grafted supports possess superior separation capabilities compared to their coated analogues. Compared to pure poly-NBE- and poly-ONDCA-grafted stationary phases, supports consisting of poly-NBE-co-ONDCA block-copolymers possess both hydrophobic and ion-exchange sites and represent optimum stationary phases for the separation of isomeric basic analytes.