Stationary Phase For High-performance Liquid Chromatography Research Articles

Single-Crystalline Covalent Organic Frameworks as High-Performance Liquid Chromatographic Stationary Phases for Positional Isomer Separation

Vigorously developing new stationary phases to meet the requirements for the separation of positional isomers that have similar physicochemical properties is still an urgent topic in separation science. Herein, a single-crystalline covalent organic framework (COF-300) packed column for the separation of positional isomers in high-performance liquid chromatography (HPLC) was reported for the first time. Benefitting from its regular shape, excellent chemical and thermal stability, microporous feature, and strong hydrophobicity of single-crystalline COF-300, the single-crystalline COF-300-packed column showed excellent resolution for the separation of positional isomers, including nitroaniline, dichlorobenzene, dibromobenzene, diiodobenzene, diethylbenzene, chloronitrobenzene, bromonitrobenzene, and iodonitrobenzene isomers, which cannot be all separated on commercial columns and a polycrystalline COF-300-packed column. Especially, the resolution values for m-/p-diiodobenzene and o-/m-diiodobenzene were 4.45 and 2.53. Moreover, the alkylbenzene, monosubstituted aromatics, polycyclic aromatic hydrocarbons, and the mixture of ethylbenzene and styrene were also baseline separated on the single-crystalline COF-300-packed column. This successful application not only confirmed the great potential of single-crystalline COFs in HPLC separation of positional isomers but also pioneered the utilization of single-crystalline COFs in separation science.

Chiral covalent organic framework-monolith as stationary phase for high-performance liquid chromatographic enantioseparation of selected amino acids.

The separation of amino acid (AA) enantiomers shows significancefor chemistry, food, and biology, but remains challenging due to their similar properties. A promising nanoporous chiral covalent organicframework (COF) as a stationary phase for high-performance liquid chromatography (HPLC) suffers from the irregularity and widely distributedparticle size of the chiral COF. Herein, we show the facile preparation of a chiral COF-monolith as a stationary phase for HPLC enantiomericseparation of AAs via orthogonal experiments. The CTzDa-monolith is prepared by the incorporation of the model chiral COF named CTzDa intothe porous poly(ethylene dimethacrylate-co-methacrylate) monolith and reveals great permeability and mechanical stability. The correspondingCTzDa-monolithic column gives better chiral HPLC separation of AAs than the commercial Poroshell 120 chiral-T column. Thermal dynamicanalysis and molecular docking calculations imply the involvement of stereoscopic hydrogen, π-π, and van der Waals interactions between theCTzDa and AAs during HPLC enantioseparation. The facile incorporation of the chiral COF into the porous monolith will promote the potential ofa chiral COF as a stationary phase for HPLC.

Preparation and application of 3-(methylene-bis(1',4'-phenylene)dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles as chiral stationary phase for HPLC.

3-(Methylene-bis(1',4'-phenylene) dicarbamate-2,3-bis(3,5-dimethylphenylcarbamate)-amylose)-2-hydroxylpropoxy-propylsilyl-appended silica particles (DMP-AM-HPS), a new type of 2, 3-regioselectively substituted amylose-immobilized chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC), have been prepared by treatment of 3-(2,3-dihydroxyl-propoxy)-propylsilyl silica particles with 2,3-bis(3,5-dimethylphenylcarbamate)-amylose and 4,4'-diphenylmethane diisocyanate. The chemical characterization of the bonded particles DMP-AM-HPS has been carried out by elemental analysis and Fourier transform infrared spectroscopic analysis. The chromatographic performance of the DMP-AM-HPS has been evaluated in HPLC under multi-mode conditions including normal phase, reversed phase, and polar organic mobile phase conditions. The DMP-AM-HPS phase has exhibited excellent selectivity in separating enantiomers of a wide range of chiral drug compounds. The result also suggests that unsubstituted C6 hydroxyl groups in the regioselectively substituted amylose not only have important contributions to chiral recognitions and chromatographic separations, but also allow the DMP-AM-HPS to be used as a new type of amylose-immobilized CSP under multi-mode mobile phase conditions in HPLC.

Preparation and application of chiral silica gel spheres based on L-glutamic

无机介孔硅球因其具有足够的机械强度、热稳定性,以及适应多种流动相的优点,成为高效液相色谱(HPLC)柱填料中使用最广泛和最重要的材料。但在此研究领域中,并未见球形的全无机手性硅胶用作HPLC手性固定相。该文以无机球形介孔硅胶作为研究对象,通过堆砌硅珠法,以硅溶胶为原料,L-谷氨酸(L-Glu)为手性源,在手性环境中制造出脲醛树脂与胶体二氧化硅混合的小球,在550 ℃高温下煅烧除去树脂部分,制备基于L-Glu的无机介孔硅胶球。通过元素分析、红外光谱、扫描电镜、透射电镜和氮气吸附等表征证明这是一种具有规则球形的手性硅胶球,其手性来源于硅胶球自身的骨架和孔结构。将L-Glu手性硅胶球作为固定相制备了HPLC色谱柱,以正己烷-异丙醇(9∶1, v/v)作为流动相,流速为0.1 mL/min,考察了该手性柱对一系列外消旋化合物的拆分性能。实验表明,该手性柱拆分了15种外消旋化合物,其中特罗格尔碱、吡喹酮、3-苄氧基-1,2-丙二醇、1,2-环氧己烷、3-羟基-2-丁酮、2-甲基四氢呋喃-3-酮、异丙基缩水甘油醚达到基线分离;还分离了10种苯系位置异构体,o,m,p-氨基苯酚、o,p-氯苯酚、o,m,p-碘苯胺、o,m,p-甲苯胺、o,m,p-二硝基苯、o,m,p-氯苯胺、o,m,p-硝基苯酚、o,m,p-溴苯胺达到基线分离。实验表明,L-Glu手性硅胶球在手性分离方面具有良好的可行性,与普通硅胶相比不需要进一步修饰就可以有较好的手性分离效果,是一种低成本、制备便捷的手性无机硅胶固定相。

Facile fabrication of silica@covalent organic polymers core-shell composites as the mixed-mode stationary phase for hydrophilic interaction/reversed-phase/ion-exchange chromatography

Covalent organic polymers (COPs) are a promising class of cross-linked polymeric networks that attracted extensive attention in separation and analysis fields. Exploring facile and convenient strategy to prepare COPs-based mixed-mode stationary phases for high performance liquid chromatography (HPLC) has seriously lagged and has never been reported. Herein, we describe a facile in-situ grow strategy for fabrication of silica@COPs core-shell composites (SiO2@TpBD-(OH)2) as a novel mixed-mode stationary phase for HPLC. Owing to the co-existing of abundant hydroxyl, carbonyl, imine, cyclohexyl groups, and benzene rings in the skeleton of COPs shell, the developed mixed-mode stationary phase exhibits hydrophilic interaction liquid chromatography (HILIC)/reversed-phase liquid chromatography (RPLC)/ion-exchange chromatography (IEX) retention mechanisms. The content of acetonitrile, pH value, and salt concentration in the mobile phase were investigated on SiO2@TpBD-(OH)2 packed column. In comparison to conventional single-mode columns, the SiO2@TpBD-(OH)2 column showed flexible selectivity, enhanced separation performance, and superior resolution for benzene homologues, polycyclic aromatic hydrocarbons, nucleosides and bases, and acidic organic compounds. The column efficiency of p-nitrobenzoic acid was up to 54440 plates per meter. The packed column also possessed outstanding chromatographic repeatability for six nucleosides and bases with the RSDs of 0.07–0.23%, 0.58–1.77%, and 0.31–1.23% for retention time, peak area, and peak height, respectively. Besides, the SiO2@TpBD-(OH)2 column offered baseline separation of multiple organic pollutants in lake water, which verified its great potential in real sample analysis. Overall, the silica@COPs core-shell composites not only provide a new candidate of mixed-mode stationary phases, but also extend the potential application of COPs in separation science.

Preparation and chromatographic properties of 1-vinyl-3-dodecylimidazole bromide silica-bonded stationary phase

As the main components of cell membranes, lipids play important roles in organisms. Lipids have been proved to be closely associated with the occurrence and development of serious diseases, such as cancers and metabolic diseases. The development of novel separation materials for use in high-performance liquid chromatography (HPLC) is essential for high-efficiency lipid separation. Such materials can promote further in-depth research of the structure and biological functions of lipids. In this study, we focused on the preparation of an ionic-liquid-modified silica-bonded HPLC stationary phase and on its chromatographic retention mechanisms and separation performances for lipids. An imidazolium-based ionic liquid with C12 side chain, viz. 1-vinyl-3-dodecylimidazole bromide (VDI), has shown good biocompatibility and has previously been used for the solubilization of membrane proteins. Thus, VDI was first exploited as the functionalized monomer for the HPLC stationary phase. It was grafted onto the surface of thiol-functionalized silica spheres by a one-step click reaction to afford a new VDI silica-bonded stationary phase (Sil-VDI). Fourier-transform infrared (FT-IR)spectroscopy and thermogravimetric analysis were used to prove the successful preparation of Sil-VDI and characterize its structure. The chromatographic retention properties of the column packed with Sil-VDI was first studied using hydrophobic alkylbenzenes. The results showed that the Sil-VDI column was a typical reversed-phase liquid chromatography retention column. Since Sil-VDI has a permanent cationic imidazole structure, it should demonstrate anion exchange retention. Thus, inorganic anions BrO3-, NO3-, and IO3- were selected to further investigate the retention mechanism of the Sil-VDI column. The results demonstrate that the Sil-VDI column also possesses ion-exchange retention mode. Thus, the Sil-VDI column has typical reversed-phase and ion-exchange mixed-mode retention characteristics. Based on the reversed-phase retention characteristics of the Sil-VDI column, hydrophobic alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), basic anilines, and benzene derivatives were selected for testing the HPLC separation performances of the Sil-VDI column. The results demonstrate that this new column gave good separation selectivity with good peak shapes. For example, PAHs like diphenyl, o-terphenyl, m-terphenyl, and triphenylene were used to investigate the chromatographic performances of the Sil-VDI column. These four PAHs were baseline separated within 7 min with good peak shapes. In addition, the positional isomers o-terphenyl and m-terphenyl show good separation efficiency, with resolution as high as 3.26. Based on the ion-exchange retention characteristics of the Sil-VDI column, inorganic anions BrO3-, NO3-, and IO3- were selected to test the separation performance of the column for ionic compounds. Using 250 mmol/L KCl solution (pH 4.1) as the mobile phase, baseline separation of the three anions was achieved within 6 min. These results demonstrate that the Sil-VDI column has good potential for separation of ionic compounds. The separation performance of the Sil-VDI column was further verified based on the separation of lipids extracted from egg yolk and lung adenocarcinoma cells. Six main chromatographic peaks could be recognized within 7 and 5 min for the lipids extracted from lung adenocarcinoma cells and egg yolk, respectively. These results primarily demonstrate that the Sil-VDI column has good potential for the separation of lipid samples. In conclusion, a new ionic-liquid-based Sil-VDI stationary phase material was successfully fabricated via a simple synthesis method. The Sil-VDI column shows good separation performances for versatile samples. In future, further research will be performed on the separation ability of the Sil-VDI column for different biological samples.

Superhydrophobic conjugated microporous polymers grafted silica microspheres for liquid chromatographic separation

Vigorously developing new high performance liquid chromatography (HPLC) stationary phases to meet the versatile separation requirements is still an important issue in the field of analytical chemistry. Conjugated microporous polymers (CMPs) are a new type of three-dimensional network porous material with high specific surface area, good chemical stability and superhydrophobicity. Herein, we firstly report the synthesis and applications of CMPs@SiO2 material for HPLC stationary phase. The CMPs@SiO2 material can be in situ fabricated via Sonogashira coupling of 1,3,5-triethynylbenzene and 1,4-diiodobenzene on the surface of spherical silica. The morphology and physicochemical properties of the synthesized stationary phase material were investigated by a series of characterization methods. Due to the superhydrophobic nature of the CMPs@SiO2 material, the packed CMPs@SiO2 HPLC column displays ultrastrong chromatographic retention and can be used for separation of both hydrophobic and hydrophilic compounds with good selectivity. Significantly, CMPs@SiO2 column can be performed for separation with pure acetonitrile as the eluent. Thus, the new column was successfully exploited for monitor and analysis of the hydrolysis of silane coupling agents. Furthermore, based on its oleophilicity, this report firstly utilized the CMPs@SiO2 material to identify and analyze the quality of cooking oils through one-step enrichment and subsequent HPLC separation. We will further exploit to fabricate versatile CMPs-based stationary phases, highlighting their potential applications in different separation scopes.

Fabrication of spherical silica amino-functionalized microporous organic network composites for high performance liquid chromatography

Microporous organic networks (MONs) are a potential class of microporous materials in analytical chemistry. As great efforts have been made in sample pretreatment and gas chromatography, the application of MONs in high performance liquid chromatography (HPLC) has largely lagged and has never been investigated. In addition, directly packing of MONs into columns for HPLC is impractical due to the high column pressure and low column efficiency resulted from the sub-micron sized and irregular MONs. To solve these issues and uncover the possibility of MONs in HPLC, here we report the fabrication of spherical silica amino-functionalized MON (SiO2@MON-NH2) composite as a novel stationary phase for HPLC. Neutral, acidic and alkaline probes were evaluated on SiO2@MON-NH2 packed column. A column efficiency of 21,246 plates per meter was obtained for n-propylbenzene. The results revealed the hydrophobic interaction was the main separation mechanism on SiO2@MON-NH2 packed column. Baseline separation of benzenediol, dichlorophenol, chlorophenol and phenylenediamine position isomers, deoxynucleosides and nucleosides was also achieved on SiO2@MON-NH2 packed column. The relative standard deviations of retention time, peak height and peak area for the studied position isomers, deoxynucleosides and nucleosides were 0.2–0.7%, 0.3–3.7% and 1.7–3.5%, respectively. The SiO2@MON-NH2 packed column also offered better resolution for dichlorophenol isomers, deoxynucleosides and nucleosides than SiO2–NH2 and commercial C18 columns. These results revealed the potential of MONs in HPLC and also provided a new way for the use of nano-sized or irregular MONs in HPLC.

Preparation and application of molecularly imprinted polymers for chiral HPLC separation of biologically active substances

Chiral separations are one of the important analytical tasks, since there are increasing demands for production of enantiomerically pure compounds. The separation and determination of enantiomers find applications in pharmaceutical and food analysis, and it is necessary to pay attention to the development and improvement of chiral analytical methods. High performance liquid chromatography (HPLC) with chiral stationary phase (CSP) based on molecularly imprinted polymers (MIPs) is perspective way. One of the main advantage of these stationary phases is the possibility of predetermining the elution order of enantiomers. The presented work is focused on the methods of preparation and the applications of selective sorption materials (MIPs) in the field of HPLC separation of biologically active substances, amino acids. This review contains comprehensive informations about MIP-amino acid synthesis: compositions of polymerization mixture (monomer, template, cross-linker, porogen), type of polymerization and polymerization conditions, what can affect final efficiency of enantioseparation. The most used porogen was toluene, crosslinker ethylene glycol dimethacrylate (EDMA) and initiator azoisobutyronitrile (AIBN). MIP CSP prepared for derivatized amino acids show better results (higher resolution) than MIP prepared for underivatized amino acids. MIP are very promising material to be used as stationary phase in HPLC, although further developments and new approaches are necessary to fully exploit their potential.

Preparation of monodisperse porous polymeric ionic liquid microspheres and their application as stationary phases for HPLC

In recent decades, ionic liquid-modified packing materials as stationary phases of high performance liquid chromatography (HPLC) have attracted widespread attention due to their comprehensive properties. In this work, monodisperse porous polymeric ionic liquid microspheres were directly prepared using a seeded emulsion polymerization method and applied as stationary phase of HPLC. The effects of porogen, monomer and crosslinker on the properties of porous P(IL-DVB) microspheres were investigated in detail. Porous P(IL-DVB) microspheres with good stability, monodispersity and relatively high specific surface area were selected as stationary phase to successfully separate benzene and its homologues, and nucleosides and alkaloids under reversed phase chromatography (RPLC) mode and hydrophilic interaction chromatography (HILIC) mode, respectively.

Enantioseparation by HPLC Using an Inorganic Chiral Mesoporous Silica with Highly-ordered Structure

Highly-ordered inorganic chiral mesoporous silica(HOCMS) has attracted substantial interest in recent decades. High performance liquid chromatography(HPLC) is the most important approach for the separation of enantiomers and herein reported an HPLC chiral stationary phase composed of HOCMS. The column was fabricated by conventional high pressure slurry packing. Eighteen racemates, including alcohols, ketones, amines, aldehydes and organic acids, were resolved on the column. Good chiral separations of hydrobenzoin, metoprolol, propranolol hydrochloride, 4-methyl-2-pentanol, omeprazole, 2,2′-furoin and ketoprofen were obtained. The relative standard devi-ations for five replicate separations of racemates were 0.1%–0.16% for retention time and 1.73%–2.64% for peak areas. The results suggest that HOCMS is a promising candidate for preparation of chiral stationary phases for HPLC.

Composite of ZIF-8 and totally porous silica gel for HPLC stationary phase

Abstract Metal-organic frameworks (MOFs) supported on silica gels have been proved to be promising stationary phases for high performance liquid chromatography (HPLC). However, up to now, the stationary phases still face the problems of uneven dispersion of MOFs on traditional spherical silica gels and the poor separation performance. In this work, the effect of the silica gel pore size on the dispersion of ZIF-8 on totally porous silica gel was systematically investigated and the highly uniform dispersion of ZIF-8 was gained on the silica gel with the pore diameter of 80 nm. Moreover, the distribution of ZIF-8 nanoparticles on the surface of wide pore silica could be further improved by adjusting the proportion of DMF and methanol solution. When the well packed ZIF-8@SiO2 composite column was used to separate hydroquinone and p-benzoquinone, its resolution reached an outstanding value of 5.47, while there was no baseline separation on the C18 column. Finally, the separation mechanism was also studied by testing the separation of the mixture of 1-phenylethanol and acetophenone. This work would provide an easy way to disperse MOFs on traditional silica gels and could provide a composite column for separation of hydroquinone and p-benzoquinone.

Selective Synthesis of Interlocked Molecules with Topological Chirality

Mechanically interlocked molecules can be chiral if each of the rings has no bilateral symmetry. Although chiral catenanes have been isolated from racemic mixtures via chromatographic techniques, these optically active molecules have not been directly synthesized until now. In this issue of Chem, Goldup and co-workers describe an auxiliary approach for the stereoselective synthesis of the topological enantiomers of chiral [2]catenanes. This methodology enables exploration of the potential applications of these chiral molecules in areas such as medicine and materials science.

An Auxiliary Approach for the Stereoselective Synthesis of Topologically Chiral Catenanes

SummaryCatenanes, molecules in which two rings are threaded through one another like links in a chain, can form as two structures related like an object and its mirror image but otherwise identical if the individual rings lack bilateral symmetry. These structures are described as “topologically chiral” because, unlike most chiral molecules, it is not possible to convert one mirror-image form to the other under the rules of mathematical topology. Although intriguing and discussed as early as 1961, to date all methods of accessing molecules containing only this topological stereogenic element require the separation of the mirror-image forms via chiral stationary phase high-performance liquid chromatography, which has limited their investigation to date. Here, we present a simple method that uses a readily available source of chiral information to allow the stereoselective synthesis of topologically chiral catenanes.

Chiral stationary phases of cellulose derived using 3,5-dimethyl phenylcarbamate

Chiral columns based on cellulose tri(3,5-dimethyl phenylcarbamate) (CTDMPC) have been extensively used for enantioseparation by high-performance liquid chromatography (HPLC). The effects of cellulose derived using different amounts of 3,5-dimethyl phenylcarbamate and silica gels prepared by different methods on the chiral separation characteristics have been investigated. Thirteen chiral chromatographic columns were prepared, and their separation capability for sixteen racemate samples was evaluated. The efficiency of enantioselective resolution followed the order trisubstituted cellulose column > disubstituted cellulose column > cellulose column. Refine silica gel and macroporous silica gel showed better performance than did coarse silica gel. The use of macroporous silica gel resulted in low column pressure. Whether the silica gels were derived by aminopropyl could affect the enantioseparations. The thirteen chiral chromatographic columns were complementary for the separation of racemates, especially the cellulose column. This is a comparative study on the preparation of chiral stationary phases for HPLC, and the findings would enable us to design and fabricate chromatographic columns.

Waxberry-like hierarchically porous ethyl-bridged hybrid silica microsphere: A substrate for enzyme catalysis and high-performance liquid chromatography

In this study, the ethyl-bridged hybrid silica microsphere with hierarchically meso-macroporous structure was initially synthesized through a method combining dispersion polymerization with sol-gel transition and phase separation. The flow-through macropores rendered the microsphere a rough surface like a waxberry, and thus the material was named as waxberry-like ethyl-bridged hybrid silica sphere (WEHS). WEHS was characteristic of appropriate alkali-stability, which was highly difficult for the pure silica. Additionally, WEHS possessed hierarchical meso- and macropores, which added additional value for faster mass transfer than the conventional fully porous silica materials. Taking the advantages of WEHS, it was successfully applied as the substrate to immobilize lipase; the prepared immobilized lipase exhibited high catalytic activity and favorable reusability under alkaline conditions, which was significant in pitch control of neutral-alkaline papermaking industry. Moreover, as the high-performance liquid chromatographic stationary phase matrix, WEHS made the separation under alkaline mobile phase into a reality for the silica-based materials. Besides, an ultra-fast and efficient separation in minutes was achieved with lower consumption of solvents and saving analytical time, which is highly desired in modern analysis. In general, WEHS was a novel and promising candidate in the myriads of silica-based materials.

Preparation and Chromatographic Features of Fibrous Core–Shell HPLC Packing Material

In this study, fibrous core–shell silica particles were successfully synthesized via a one-step oil–water biphase stratification coating strategy. The core–shell silica particles were composed of 3-µm non-pore silica cores and thin shells (50–100 nm), which have radial-like direct channels and a large pore size (19.89 nm). The fibrous core–shell silica particles were further modified by n-octadecyltrichlorosilane and used as stationary-phase media in high-performance liquid chromatography (HPLC). The chromatographic properties of the particles were systematically studied in small-molecule and protein separation processes. The results showed that the back pressure was as low as 8.5 MPa under the 1.0-mL min−1 flow velocity. Furthermore, fibrous core–shell silica particles with an 80-nm shell were used for separating seven small molecules within 10 min and six proteins within 6 min. This work demonstrates that the fibrous core–shell silica particles could be used as an HPLC stationary phase with good performance and low back pressure, and that they have great potential for application to HPLC separation in the future.

Synthesis and evaluation of porous polymethylsilsesquioxane microspheres as low silanol activity chromatographic stationary phase for basic compound separation

Polymethylsilsesquioxanes (PMSQ) are potentially useful materials for liquid chromatography owing to their unique chemical, electrical and mechanical properties. Surprisingly however, no systematic studies on the use of spherical PMSQ particles as chromatographic packing have been reported. Accordingly, we present a comprehensive study aimed to characterize the chromatographic properties of this material in high performance liquid chromatography (HPLC) and to compare them with those observed on methyl (C1) bonded silica phase under comparable conditions. Porous spherical particles were synthesized by a two-step hydrolysis and condensation procedure from methyltrimethoxysilane (MTMS) as a sole precursor. The as-synthesized microspheres possess spherical shape, narrow size distribution, mesoporous structure, high surface area (817 m2 g−1) and reasonable carbon load (16.6%). They can be used directly as the HPLC stationary phase without the need for size classification. The PMSQ phase exhibits typical reversed-phase chromatographic properties with higher methylene selectivity and low silanol activity compared with the C1 column. The retention mechanism for basic compounds was systematically evaluated by studying the effect of pH, ionic and solvent strength of the mobile phase. Basic compounds displayed lower retention factor and symmetric peak shape on the PMSQ column whereas longer retention and strong tailing peaks were observed on the C1 column. The difference in retention behavior between the two columns is explained in terms of different principal retention mechanisms. Because of the low silanol activity, retention of basic compounds on the PMSQ column is governed solely by a reversed-phase mechanism. By contrast, multiple interactions including reversed-phase, cation exchange and simultaneous reversed-phase/cationic exchange interaction contribute to the retention on the C1 column, as previously observed on other silica based reversed-phases. Furthermore, the PMSQ phase exhibited significantly enhanced stability under alkaline conditions compared with its silica-based counterpart. Taken together, the favorable morphology and pore structure combined with the benefits of low silanol activity, high pH stability and prolonged column lifetime make the newly developed PMSQ phase a promising and viable alternative to silica based reversed-phase packings for separation of basic compounds.

Immobilization of helical poly(phenylacetylene)s having l-phenylalanine ethyl ester pendants onto silica gel as chiral stationary phases for HPLC

Novel one-handed helical copoly(phenylacetylene)s bearing a small amount of 3-(triethoxysilyl)propyl residues (CPAs 1–4) were synthesized, and efficiently chemically immobilized onto silica gel by the intermolecular polycondensation of the triethoxysilyl groups. Their chiral recognition abilities were evaluated as immobilized-type chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC). These immobilized-type CSPs showed different chiral recognition abilities from the corresponding coated-type CSPs, which may be ascribed to the conformational change in the copoly(phenylacetylene)s during the immobilization process according to the diffuse reflectance circular dichroism (DRCD) measurement of the copolymer. In addition, the immobilized-type CSPs showed a universal solvent tolerability, for instance, CHCl3-containing eluents that cannot be used with the corresponding coated-type CSPs could now be used for the immobilized-type CSPs so that the chiral recognition of i-CSP-2 for the racemic 1-(9-anthyl)-2,2,2-trifluoroethanol (5) was improved with separation factors comparable or higher than those obtained on the popular polysaccharide-based CSPs. The intermolecular polycondensation of the triethoxysilyl groups of the copoly(phenylacetylene)s is a valuable immobilization method for poly(phenylacetylene)-based CSPs.

Synthesis of monodisperse silica microspheres and modification with diazoresin for mixed-mode ultra high performance liquid chromatography separations.

Monodisperse silica particles with average diameters of 1.9-2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self-assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin-modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin-modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π-π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C60 and C70 were also well separated by ultra-high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin-modified silica stationary phase shows ultra-high efficiency compared with the commercial C18 -silica high-performance liquid chromatography stationary phase with average diameters of ∼5 μm.