超分子化合物毛细管电色谱固定相的研究进展

超分子化学是一门研究分子间特定识别能力的新兴学科,超分子化合物所具有的主-客体识别能力为高选择性的色谱分离提供了广阔的发展前景。毛细管电色谱是近年来发展起来的一种高效、高选择性的微分离技术,电色谱固定相是该技术的核心部分,一直是研究的热点。本文综述了1998年以来环糊精、杯芳烃、冠醚以及大环多胺等4种超分子化合物用作毛细管电色谱固定相的研究进展情况。     

Sol-gel stationary phases for capillary electrochromatography

A review is presented on the current state of the art and future trends in the development of sol-gel stationary phases for capillary electrochromatography (CEC). The design and synthesis of stationary phases with prescribed chromatographic and surface charge properties represent challenging tasks in contemporary CEC research. Further developments in CEC as a high-efficiency liquid-phase separation technique will greatly depend on new breakthroughs in the area of stationary phase development. The requirements imposed on CEC stationary phase performance are significantly more demanding compared with those for HPLC. The design of CEC stationary phase must take into consideration the structural characteristics that will provide not only the selective solute/stationary phase interactions leading to chromatographic separations but also the surface charge properties that determine the magnitude and direction of the electroosmotic flow responsible for the mobile phase movement through the CEC column. Therefore, the stationary phase technology in CEC presents a more complex problem than in conventional chromatographic techniques. Different approaches to stationary phase development have been reported in contemporary CEC literature. The sol-gel approach represents a promising direction in this important research. It is applicable to the preparation of CEC stationary phases in different formats: surface coatings, micro/submicro particles, and monolithic beds. Besides, in the sol-gel approach, appropriate sol-gel precursors and other building blocks can be selected to create a stationary phase with desired structural and surface properties. One remarkable advantage of the sol-gel approach is the mild thermal conditions under which the stationary phase synthesis can be carried out (typically at room temperature). It also provides an effective pathway to integrating the advantageous properties of organic and inorganic material systems, and thereby enhancing and fine-tuning chromatographic selectivity of the created hybrid organic-inorganic stationary phases. This review focuses on recent developments in the design, synthesis, characterization, properties, and applications of sol-gel stationary phases in CEC.     

Polar stationary phases for capillary electrochromatography

This review article summarizes the variety of polar stationary phases that have been employed for capillary electrochromatographic separations. Compared with reversed-phase stationary phases, the polar alternatives provide a completely different retention selectivity towards polar and charged analytes. Different types of polar stationary phases are reviewed, including the possible retention mechanisms. Electrochromatographic separations of polar solutes, peptides, and basic pharmaceuticals on polar stationary phases are presented.     

Recent developments in the field of monolithic stationary phases for capillary electrochromatography

This review summarizes the contributions to the rapidly growing area of monolithic columns based on both silica and synthetic polymers for capillary electrochromatography and chip electrochromatography, with a focus on those published during the year 2004. A wide variety of both modified approaches to the "old" monoliths and new monoliths have been reported despite the very short period of time covered. This demonstrates that monolithic stationary phases have become a well-established format in the field of electrochromatography. The simplicity of their preparation as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials.     

Polymeric monolithic stationary phases for capillary electrochromatography

This review summarizes the contributions of a number of groups working in the rapidly growing area of monolithic columns for capillary electrochromatography (CEC), with a focus on those prepared from synthetic polymers. Monoliths have quickly become a well-established stationary phase format in the field of CEC. The simplicity of their in situ preparation method as well as the good control over their porous properties and surface chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. A wide variety of approaches as well as materials used for the preparation of the monolithic stationary phases are detailed. Their excellent chromatographic performance is demonstrated by numerous separations of different analytes.     

Polymer-brush stationary phases for open-tubular capillary electrochromatography

Synthesis of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes from the inside of silica capillaries by surface-initiated atom transfer radical polymerization (ATRP) yields unique stationary phases for open-tubular capillary electrochromatography (OT-CEC). Although PHEMA brushes have only a small effect on the separation of a set of phenols and anilines, derivatization of PHEMA with ethylenediamine (en) allows baseline resolution of several anilines that co-elute from bare silica capillaries. Derivatization of PHEMA with octanoyl chloride (C8-PHEMA films) affords even better resolution in the separation of a series of phenols and anilines. Increasing the thickness of C8-PHEMA coatings by a factor of 2 enhances resolution for several solute pairs, presumably because of an increase in the effective stationary phase to mobile phase volume ratio. Thus, this work demonstrates that thick polymer brushes provide a tunable stationary phase with a much larger phase ratio than is available from monolayer wall coatings. Through appropriate choice of derivatizing reagents, these polymer brushes should allow separation of a wide range of neutral molecules as well as compounds with similar electrophoretic mobilities.     

Monolithic enantiomer-selective stationary phases for capillary electrochromatography

Monolithic materials have become a well-established format for stationary phases in the field of capillary electrochromatography. Four types of monoliths, namely particle-fixed, silica-based, polymer-based, and molecularly imprinted monoliths, have been utilized as enantiomer-selective stationary phases in CEC. This review summarizes recent developments in the area of monolithic enantiomer-selective stationary phases for CEC. The preparative procedure and the characterization of these columns are highlighted. In addition, the disadvantages and limitations of different monolithic enantiomer-selective stationary phases in CEC are briefly discussed.     

Recent progress in capillary electrochromatography

Capillary electrochromatography (CEC) continues to captivate many separation scientists. A remarkable activity is apparent from the numerous publications in the literature using CEC. A review of the most recent progress in CEC is presented herein, covering an extensive fraction of the literature on CEC published from the year 1997 until the beginning of 2000. Most of the recent developments have concentrated on column technology.     

Acrylamide-based monoliths as robust stationary phases for capillary electrochromatography

A method is described for the synthesis of rigid, macroporous polymers (monoliths) to be used as stationary phases in capillary electrochromatography (CEC). The procedure reproducibly results in columns with good mechanical and chemical stability. Once the procedure was optimized, it yielded the desired CEC columns in nearly 100% of the cases. The batch-to-batch standard deviation of the migration of the electroosmotic flow (EOF) marker for nine randomly chosen columns was 5%. The polymerization is carried out inside the capillary, an aqueous phase is used as solvent. Monomers based on acrylamides with varying hydrophilicity were used to introduce the interactive moieties together with piperazine diacrylamide as cross-linker and vinylsulfonic acid as provider of the charged, EOF-producing moieties. The pore size of the monoliths was adjusted by adding varying amounts of ammonium sulfate to the reaction mixture. In this manner, the average pore size of a given monolith could be reproducibly adjusted to values ranging from 50 nm to 1.3 microm. The procedure was optimized for four particular types of monoliths, which differed in hydrophobicity. The latter was adjusted by introducing suitable co-monomers, such as alkyl chain-bearing molecules, into the monolithic structure. Attempts to systematically investigate the chromatographic behavior of the monolithic stationary phases were made, using a model mixture of aromatic compounds as sample. The standard deviations for the run-to-run reproducibility of the retention times for unretained and retained analytes were <1.5%. Flat Van Deemter curves were measured even at elevated flow-rates (2 mm/s). Plate heights between 10 and 15 microm were measured in this range. The retention order was taken as the principal indication for the chromatographic mode. The separation was found to be governed neither by pure reversed-phase nor by pure normal-phase chromatography, even on monoliths, where large amounts of C6 ligands had been introduced.     

Monolithic stationary phases for liquid chromatography and capillary electrochromatography

A monolithic stationary phase is the continuous unitary porous structure prepared by in situ polymerization or consolidation inside the column tubing and, if necessary, the surface is functionalized to convert it into a sorbent with the desired chromatographic binding properties [J. Chromatogr. A 855 (1999) 273]. Monolithic stationary phases have attracted considerable attention in liquid chromatography and capillary electrochromatography in recent years due to their simple preparation procedure, unique properties and excellent performance, especially for separation of biopolymers. This review summarizes the preparation, characterization and applications of the monolithic stationary phases. In addition, the disadvantages and limitations of the monolithic stationary phases are also briefly discussed.     

Polymerised bicontinuous microemulsions as stationary phases for capillary electrochromatography

Summary Polymerisation of bicontinuous microemulsions yields porous monolithic structures with well defined pore sizes that are potentially suitable for use as stationary phases for capillary electrochromatography (CEC). A variety of pore sizes can be achieved by altering the composition of the microemulsion, which typically consists of butyl methacrylate (BMA) and ethylene glycol dimethacrylate (EGDMA) as the polymerisable oil phase. The aqueous phase consists of water, a surfactant (sodium dodecyl sulphate, SDS) and a co-surfactant (1-propanol). 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) is also added to provide charges along the polymer backbone to allow electroosmotic flow (EOF) to occur. SEM analysis shows that in-situ polymerisation yields a monolithic structure with a porous topography. Investigations have shown that these monoliths are easy to prepare, robust and suitable for the separation of phthalates. They generate higher linear velocities than are achieved using the silica based HPLC packings normally used for CEC.     

Recent highlights in stationary phase design for open-tubular capillary electrochromatography

This review examines the most recent innovations made to achieve high performance in open-tubular capillary electrochromatography (OT-CEC) separations, focusing on the ingenious chemical and physical solutions made to increase the surface area and equip the stationary phase with exploitable selectivity. Among the approaches taken are chemically bonded ligands, etching with chemical bonding, sol-gels, molecularly imprinted polymers, porous layers, physically attached or adsorbed phases, and nanoparticle coatings. Particularly noteworthy are modern developments with macrocyclic receptor ligands, nanoparticles and open channel electrochromatography on-chip.     

Investigation of capillary electrochromatography with brush-type chiral stationary phases

Fused-silica capillaries (100 microm ID) were packed with the (3R, 4S)-Whelk-O chiral stationary phase (CSP) bonded on 3.0 microm silica particles. The enantiomers of 41 neutral analytes containing stereogenic centers, axes or planes were examined by packed capillary electrochromatography. More than 30 of these were cleanly resolved, owing to the selectivities and efficiencies afforded by this CSP. High reproducibility with no indication of diminished performance was observed using the same capillary for hundreds of runs (including intermediate change of the buffer system) over a period of several weeks. Acetate, 2-(N-morpholino)ethanesulfonic acid, or phosphate buffers, each modified with either acetonitrile or methanol, were used as mobile phases. The influence of buffer concentration, modifier amount, temperature, applied voltage, and pH on performance of the brush-type CSP was investigated.     

Enantiomer separations by capillary electrochromatography using chiral stationary phases

The applicability of capillary electrochromatography (CEC) using packed capillary column to enantiomer separations was investigated. As chiral stationary phases, OD type packing materials of 5 and 3 microm particle diameters, originally designed for conventional high-performance liquid chromatography (HPLC) were employed. The chiral packing materials were packed by a pressurized method into a 100 microm I.D. fused-silica capillary. Several racemic enantiomers, such as acidic, neutral and basic drug components, were successfully resolved, typically by using acidic or basic solutions containing acetonitrile as mobile phases. The separation efficiencies for some enantiomers in the chiral CEC system using the 5 microm OD type packing were superior to those obtained in HPLC using chiral packings. The plate heights obtained for several enantiomers were 8-13 microm or the reduced plate height of 1.6-2.6, which indicates the high efficiency of this chiral CEC system.     

Development and application of polymeric monolithic stationary phases for capillary electrochromatography

Monolithic columns for capillary electrochromatography are receiving quite remarkable attention. This review summarizes results excerpted from numerous papers concerning this rapidly growing area with a focus on monoliths prepared from synthetic polymers. Both the simplicity of the in situ preparation and the large number of readily available chemistries make the monolithic separation media a vital alternative to capillary columns packed with particulate materials. Therefore, they are now a well-established stationary phase format in the field of capillary electrochromatography. A wide variety of synthetic approaches as well as materials used for the preparation of the monolithic stationary phases are presented in detail. The analytical potential of these columns is demonstrated with separations involving various families of compounds and different chromatographic modes.     

Recent progress in polar stationary phases for CEC

This review summarizes most of the recent developments in the preparation and application of polar stationary phases for CEC covering the literature published since the year 2004. These polar stationary phases have been adopted for separation of analytes by the modes of packing column CEC, open-tubular CEC (o-CEC) and monolithic column CEC. Currently, development of o-CEC using biomolecules, such as protein and DNA, as the immobilized ligands is highlighted partly due to the simplicity of preparation. Furthermore, monolithic columns have been extended quickly, particularly inorganic materials-based monoliths, such as silica, zirconia, hafnium, etc., as an alternative to packed columns have been developed quickly.     

Enantioseparations in non-aqueous capillary electrochromatography using polysaccharide type chiral stationary phases

Enantioseparations of chiral compounds with different structures were studied in non-aqueous capillary electrochromatography (NAQ CEC). Three different polysaccharide derivatives, cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD), amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD) and cellulose tris(4-methylbenzoate) (Chiralcel OJ) were used as chiral stationary phases (CSPs). Methanolic or ethanolic ammonium acetate solutions served as a mobile phase. The effect of the type of the CSP, the loading of the chiral selector on wide-pore aminopropyl derivatized silica gel and operational parameters such as apparent pH, applied voltage, etc. on the EOF and chromatographic characteristics (alpha, N, Rs) were studied. NAQ CEC represents a valuable alternative and an extension to chiral separations by HPLC with common-size columns as well as to capillary LC and CEC in aqueous buffers.     

Histidine-functionalized silica and its copper complex as stationary phases for capillary electrochromatography

A histidine-functionalized silica was prepared by covalent bonding of the functional groups to silane-treated silica gel. Conversion of functional groups was confirmed by infrared (IR) spectra, elemental analysis, and potentiometry. The functionality of the silica gel is 0.293 mmol g(-1). The coordination behavior of the histidine-functionalized silica was investigated by metal capacity and electron paramagnetic resonance (EPR). EPR measurements at different copper loadings were made. The results showed that the copper histidine complex might be distorted tetragonal. Both histidine-functionalized silica and its copper complex were employed as stationary phases for packed capillary electrochromatography (CEC). Electrical current was found helpful for evaluating the properties of frit construction and the stationary phase packing. Test samples include neutral compounds, inorganic anions and organic anions. Factors influencing the separation behavior have been studied. With copper-histidine functionalized silica under the condition of citrate buffer (10 mM, pH 4.0) and applied voltage of -20 kV, the separation of benzoic acid, D- and L-mandelic acid, phthalic acid and salicylic acid could be achieved within 12 min. The column efficiency for these acids was more than 1.2 x 10(5) plates m(-1), except salicylic acid.     

吸附固定相开管毛细管电色谱方法的建立（英文）

 首次将管壁吸附作用作为开管毛细管电色谱固定相制备的推动力,成功地建立了称为“吸附固定相开管毛细管电色谱”的一种新方法。原理是：选择合适的条件,让荷正电的化合物在毛细管管壁上充分吸附,直接用吸附层作为固定相。目前,已有数类化合物被用作固定相物质,其中包括阳离子表面活性剂如十六烷基三甲基溴化铵（CTAB）、碱性蛋白质如溶菌酶和细胞色素C、碱性小肽如赖氨酸-酪氨酸和赖氨酸-丝氨酸-酪氨酸、以及碱性氨基酸如L-赖氨酸。CTAB吸附固定相用于分离电中性化合物,其它吸附固定相用于手性分离。     

Recent progress in enantiomeric separation by capillary electrochromatography

Recent progress in enantiomeric separations by capillary electrochromatography (CEC) is reviewed. The development of simple and robust CEC column technologies plays an important role for popularization of CEC. During the last several years, various approaches for the preparation of enantioselective columns have been reported. Currently, the monolithic column technology (continuous beds) represents the most advanced approach for the preparation of CEC columns. The development of new chiral stationary phase used for CEC is another important issue in this field. Fundamental investigations on electrochromatographic behaviors of various CSPs are necessary in order to understand the separation mechanism and thus improve the separation performance. Some chiral stationary phases performed better under nonaqueous CEC conditions than reversed-phase conditions. Coupling CEC with mass spectrometry (MS) provides a powerful tool for enantiomeric separation. Finally, some applications of enantiomeric separation by CEC are summarized.