Versatile Stationary Phases Research Articles

Influence of the Polymerization Parameters on the Porosity and Thermal Stability of Polymeric Monoliths.

Rigid porous polymeric monoliths are robust, highly efficient, versatile stationary phases. They offer simple preparation and convenient modification provided by a whole range of synthesis factors, e.g., starting monomers, cross-linkers, initiators, porogens, polymerization techniques, and temperature. The main aim of this study was to synthesize polymeric monoliths and determine the correlation between polymerization parameters and the porosity and thermal stability of the obtained materials. Polymeric monoliths were synthesized directly in HPLC columns using N-vinyl-2-pyrrolidone (NVP) and 4-vinylpiridine (4VP) as functional monomers, with trimethylolpropane trimethacrylate (TRIM) serving as the cross-linking monomer. During copolymerization a mixture of cyclohexanol/decane-1-ol was used as the pore-forming diluent. Polymerization was carried out at two different temperatures: 55 and 75 °C. As a result, monoliths with highly developed internal structure were synthesized. The value of their specific surface area was in the range of 92 m2/g to 598 m2/g, depending on the monomer composition and polymerization temperature. Thermal properties of the obtained materials were investigated by means of thermogravimetry (TG). Significant differences in thermal behavior were noticed between monoliths synthesized at 55 and 75 °C. Additionally, the poly(NVP-co-TRIM) monolith was successfully applied in GC analyses.

Innovative preparation of ureido/dodecyl dual-functionalized silica as a versatile mixed-mode stationary phase for high-resolution chromatographic separations

Developing a versatile stationary phase to achieve the purpose of efficiently separating various target analytes is of great significance. In this work, ureido/dodecyl dual-functionalized silica (Sil-Ur-DD) was synthesized and employed as a new mixed-mode stationary phase for high-resolution chromatographic analysis. It was observed that multiple interactions, including hydrophobic, hydrophilic, hydrogen bonding, electrostatic and π-π interactions, contributed to the retention. Nucleosides and nucleobases could be effectively determined in hydrophilic interaction chromatography mode, and the separation performance of the Sil-Ur-DD was found to be even superior to that of the commercial XAmide column. Environmental endocrine disruptors, including alkylphenols, bisphenols, steroid hormones and phthalates, were more favorably separated in reversed-phase chromatography mode with highly aqueous mobile phases compared with the commercial C18-silica column. The experimental results indicated that the combined effect of ureido and long-chain alkyl groups obviously enhanced separation efficiency and selectivity. More significantly, the proposed method concerning the preparation of an efficient separation material with powerful separation ability is economical and environmentally friendly, which provides a proven and effective way for the recycling and utilization of the discarded chromatographic packing materials, thereby showing a good application prospect.

Synthesis and chromatographic evaluation of poly(pentabromostyrene)-silica composite: A versatile stationary phase for separating both polar and non-polar aromatic compounds

Polymer-silica composite materials have been witnessed as one of the most promising chromatographic packing materials. The demands of novel stationary phases are always existing due to the requirements for the separation of special samples. In our present work, the novel poly(pentabromostyrene)-silica composite stationary phases were successfully prepared by surface initial free-radical polymerization. The polymer chains bonding on the surface of the poly(pentabromostyrene) contain plenty of phenyl moiety, which provide hydrophobic and π-π interactions between the stationary phase and analytes. Besides, the bromide atoms, existing in the polymer, provide extra polar interaction with polar or easily polarized analytes. Compared with the typical C18 stationary phase, the novel stationary phase showed special separation selectivity. Samples, including polycyclic aromatic hydrocarbons, phenols, anilines, amino acids, halogenated benzenes, acetophenone derivatives, benzene homologous compounds, were all well separated by the new stationary phase. Also, the great stability (0.13% ≤ RSDs ≤ 0.98%, n = 5) of packed columns and the good synthesis repeatability were demonstrated. Finally, the new columns were applied to the separation of fullerenes. The loading ratio reached 2.67% (36 mg of fullerenes was loaded onto the column packed with 1.35 g stationary phase), with high yield (86.3%) of high pure C60 (>95%). This novel stationary phase has a great potential to be a complementary to traditional C18 column and a special column for fullerenes separation.

Preparation and Evaluation of a Cholesterol Derivatized β-Cyclodextrin-bonded Phase for Achiral and Chiral HPLC.

A cholesterol mono-derivatized β-cyclodextrin was synthesized and bonded onto silica gel (SBA-15) to obtain a cholesterol mono-derivatized β-cyclodextrin-bonded stationary phase (CHCDP). The chemical structures of mono-derivatized β-cyclodextrin and CHCDP were characterized by infrared spectroscopy, mass spectrometry, elemental analysis and thermogravimetric analysis, correspondingly. Furthermore, the separation ability of CHCDP in terms of achiral compounds was systematically evaluated by separating benzene homologs, polycyclic aromatic hydrocarbons (PAHs) and some positional isomers. As a result, CHCDP completely separated five benzene homologs and nine PAHs within 30 min under the reversed-phase. In addition, the chiral chromatographic property of CHCDP was also evaluated by separating some racemic compounds including flavanones, triazoles, β-blockers, etc. The results showed that the CHCDP exhibited high enantioselectivities towards most of selected analytes. The enantioresolutions were in the range from 1.43 to 2.51 on CHCDP. Especially the resolutions of 2'-hydroxyflavanone, hexaconazole, Dns-serine and atenolol were as high as 1.94, 1.91, 2.15 and 1.57, respectively. Obviously, the CHCDP was a versatile stationary phase with chiral and achiral separation capabilities in multi-mode chromatography, which was related to the introduction of cholesterol to the port of cyclodextrin, enhancing the hydrophobic interaction of cyclodextrin with achiral compounds, while maintaining the inclusion complexation of it with chiral compounds as well.

A peculiar chromatographic selectivity of porous graphitic carbon during the separation of dileucine isomers

Porous graphitic carbon is a versatile stationary phase for high-performance liquid chromatography which performs especially well for isomeric separations. Shape-sensitivity of the stationary phase is caused by a steric effect when a molecule interacts with a flat carbon surface. It follows that branched, non-flat molecules are eluted much earlier than flat or linear molecules. In this short communication we show that if a molecule has a highly ionizable group, the “shape” of a molecule part which is farther from the ionizable group affects retention much more than the “shape” of a molecule part which is closer to the ionizable group. Dipeptides which consist of tert-leucine and norleucine were used as an example. Basic and acidic eluents were used. Retention strongly depends on whether a norleucine or tert-leucine residual is located near the non-ionized side in an eluent for both basic and acidic eluents. A residual located on the opposite side is less important. To investigate the possible causes of this peculiar retention behavior we compared the retention behavior of these dipeptides for porous graphitic carbon with the behavior for other types of stationary phases and with the calculated physicochemical properties. Strong and complex dependence of elution order on a mobile phase composition is demonstrated. The separation of other dileucine isomers is also considered. The applicability of porous graphitic carbon for the separation of complex mixtures of isomeric peptides is discussed.

Polyhedral oligomeric silsesquioxane grafted silica-based core-shell microspheres for reversed-phase high-performance liquid chromatography.

Polyhedral oligomeric silsesquioxane (POSS) was used to modify spherical silica to fabricate core-shell POSS@SiO2 microspheres. The material was characterized by Fourier transform infrared experiments, scanning electron microscopy, thermogravimetric analysis and elemental analysis. The material was also used as astationary phase for HPLC separation. The POSS@SiO2 column exhibits areverse-phase liquid chromatography (RPLC) retention mechanism. The column efficiency of alkylbenzenes reaches 67,200 plates·m-1. The POSS@SiO2 column was also utilized for separation of basic anilines and polycyclic aromatic hydrocarbons. Compared with the commercial C8 column, the POSS@SiO2 column exhibits enhanced separation selectivity. The column was also used for the separation of synthetic cytokinins 6-benzylaminopurine and 6-furfurylaminopurine in bean sprout after extraction. In addition, the methacrylate groups on the surface of the POSS@SiO2 microsphere were further functionalized so as to facilitate the fabrication of versatile stationary phases with various separation mechanisms. Graphical abstract Schematic presentation of the two-stepfabrication of polyhedral oligomeric silsesquioxane grafted silica-based (POSS@SiO2) core-shell microspheresfor use in HPLC.

Recent highlights in electro-driven separations- selected applications of alkylthiol gold nanoparticles in capillary electrophoresis and capillary electro-chromatography.

To date, alkylthiol gold nanoparticles (AuNPs) have been widely used in electro-chromatographic separation techniques as a viable alternative to traditional stationary phases. This is mainly due to their stability, chemical inertness, ease of functionality, increased phase ratio, ability to form self-assembled monolayers. They also yield versatile stationary phases with highly specific targeted functionalities. At the nanoscale region, the chemical and physical properties of a molecule display different attributes to that of the parent molecules or material, hence these features can be harnessed in electro-driven chromatographic separations. Application areas illustrating the use of AuNPs in separation science continue to grow and expand to cover many different kinds of analysis. The last decade has witnessed a successful trend in miniaturisation of chemical separation systems toward the micro and nanoscale ranges. Nanoparticle-based stationary phases fit well with performing chemical separations on microfluidic and capillary platforms. In this review the theory of the use of alkylthiol gold nanoparticles in electro-chromatographic driven separation methods will be discussed. This will be followed by details of recent and selected applications showing alkylthiol gold nanoparticles in capillary electrophoretic and open-tubular electro-chromatographic separations. This review will focus solely on alkylthiol based gold nanoparticles, therefore other kinds of chemical moieties bonded to gold nanoparticles are outside the scope of this review. Finally the future outlook of this exciting technology will be outlined in some detail in the final section.

Hydrosilylated allyl‐silica hybrid monolithic columns

Organic-inorganic silica hybrid monolithic columns were synthesized containing an allyl pendant. The ally-monolithic columns were then modified via hydrosilylation reactions to introduce further surface functionalization. The approach was demonstrated by functionalizing allyl-monolytic columns with n-octyl-dimethylsilane (C(8)-DMS) and benzyl-dimethylsilane (benzyl-DMS). Of the surface available ally groups on the hybrid monolith (i.e., 6.79 micromol/m(2)), 31.3% reacted via hydrosilylation, resulting in a C(8) surface coverage of 2.12 micromol/m(2). When using benzyl-DMS, a surface coverage of 1.95 micromol/m(2) was calculated for the benzyl groups. The retentivity of the hybrid monolithic columns increased considerably after the hydrosilylation, as monitored by CLC and CEC. The largest increase in retention was observed with the C(8) modified monolith. The hybrid monolithic columns showed higher hydrolytic stability than monolithic columns prepared by the conventional silanoxane bonding of alkyl chlorosilanes modification. The ally-monolithic column provides a platform for the fabrication of hybrid monoliths that can be conveniently modified by means of hydrosilylation, tailoring the surface of the material. The approach is a promising method to prepare hybrid monolithic columns with versatile stationary phases in a simple and efficient manner.

ChemInform Abstract: Immobilized Porphyrins as Versatile Stationary Phases in Liquid Chromatography

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Immobilized Porphyrins as Versatile Stationary Phases in Liquid Chromatography

The preparation, characterization and potential liquid chromatographic applications of various porphyrin-silica stationary phases are reviewed. These new phases are synthesized by covalently linkin...