Cyclodextrin-modified monolithic columns for resolving dansyl amino acid enantiomers and positional isomers by capillary electrochromatography

We describe beta- and gamma-cyclodextrins (beta- and gamma-CD)-modified monolithic columns prepared by sol-gel process and chemical modifications. The monolithic silica column was fabricated inside a fused-silica capillary with 100 microm inner diameter by sol-gel process. The monolithic silica matrix was chemically modified chiral selectors of beta- or gamma-CDs with a spacer of 3-glycidoxypropyltrimethoxysilane by on-column reactions. Gamma-CD-modified monolithic column has successfully been applied for the separation of dansyl amino acid enantiomers. Beta-CD-modified monolithic column has been used for the separation of the positional isomers of o-, m-, and p-cresols and the enantioseparation of racemates of benzoin and several dansyl amino acids by capillary electrochromatography, respectively. For the separation of neutral positional isomers, a positive electric field was applied. However, for the separation of negatively charged analytes, a negative electric field was applied at the inlet of column. The separation efficiency of 5.0 x 10(4) theoretical plates/m for dansyl-L-threonine was obtained at electric field strength of -300 V/cm in the mobile phase of 50 mM 2-(N-morpholino)ethanesulfonic acid (MES)-Tris/methanol (70/30) buffer at pH 7.0. L-enantiomers were eluted as the first peak. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pores.     

双苯基杂化整体柱的制备及毛细管电色谱性能研究

以苯基三乙氧基硅烷(PTES)和1,4-双三乙氧基硅基苯(BTEB)为反应单体,分别采用盐酸和十二胺为催化剂,通过两步酸碱催化的溶胶-凝胶法制备了新型双苯基杂化硅胶毛细管电色谱整体柱。分别采用扫描电镜、红外光谱和压汞法对材料的结构特性进行了表征。结果表明,所制备的材料具有特定的网络结构特征,孔径主要分布在3.4μm左右,材料的总孔容为3.5 cm3/g,比表面积为145 m2/g。新型整体柱能够很好地分离烷基取代苯、稠环芳烃、取代苯胺和硝基苯酚异构体。整体柱重复性实验表明,6种苯的同系物保留时间和容量因子的相对标准偏差分别小于0.61%和0.30%(n=8)。不同批次的整体柱的保留时间和容量因子的相对标准偏差分别小于7.2%和5.6%(n=3)。     

Reduced-bore monolithic silica column modified with C8-TEOS for reversed-phase electrochromatography

Monolithic silica columns of 2.7 mm ID were prepared and derivatized with C8-TEOS and TEOS by on-column sol-gel reaction. These C8 large diameter monolithic silica columns gave 21 000 theoretical plates for aromatic hydrocarbons in 60% acetonitrile and 40% Tris-HCI buffer. The surface areas as well as the separation reproducibility were improved on coating by the sol-gel approach. Joule heating was greatly reduced by using monolithic columns to which fine quartz sand had been added during column preparation. Since this is a preliminary investigation on a monolithic column with such a large inner diameter, the separation efficiency was not so high as that presently achieved in normal capillary electrochromatography (CEC). However, use of the columns improved sample loadability and concentration detectability of electrochromatography, and semi-preparative separations could be performed.     

Chemically modified chiral monolithic silica column prepared by a sol-gel process for enantiomeric separation by micro high-performance liquid chromatography

In this work a new type of chiral monolith silica column was developed for the chiral separation by micro high-performance liquid chromatography (micro-HPLC). The chiral monolith column with a continuous skeleton and a large through-pore structure was prepared inside a capillary of 100 microm I.D. by a sol-gel process, and chemically modified with chiral selectors, such as L-phenylalaninamide, L-alaninamide and L-prolinamide, on the surface of the monolithic silica column. Based on the principle of ligand exchange, these chiral monolithic columns were successfully used for the separation of dansyl amino acid enantiomers, as well as hydroxy acid enantiomers by micro-HPLC. The chromatographic conditions, the enantioselectivity and the performance of columns are discussed.     

Monolithic silica columns with mixed mode of hydrophilic interaction and weak anion-exchange stationary phase for pressurized capillary electrochromatography

A silica-based monolithic column as polar stationary phase is proposed for pressurized CEC (pCEC). The monolithic silica matrix from a sol-gel process was chemically modified by 3-aminopropyltrimethoxysilane to produce a column for hydrophilic interaction applications. The amino groups on the surface of the polar stationary phase generated anodic EOF under acidic conditions and served at the same time as a weak anion-exchanger. The anion solutes such as nucleotides were separated by the mixed mode mechanism, which comprised hydrophilic interaction, weak anion-exchange, and electrophoresis. The influences of buffer concentration and organic modifier content on the separation of nucleotides by pCEC have been investigated. In addition, the monolithic silica columns were also able to separate various polar compounds such as phenols, nucleic acid bases, and nucleosides in the hydrophilic interaction CEC mode.     

溶胶-凝胶法制备高热稳定性的毛细管气相色谱柱

毛细管气相色谱柱的传统制备工艺都较为复杂,周期较长,同时固定相和石英毛细管内壁间通常并无化学键生成,在较高温度下使用时固定相的流失严重,导致这类色谱柱的最高允许使用温度不很高．溶胶-凝胶法是一种快速有效的制备色谱柱的新技术,近年来经常应用于高效液相色谱、毛细管电色谱和固定相微萃取等分析化学的许多领域．在气相色谱方面,溶胶-凝胶端羟基聚硅氧烷柱、溶胶-凝胶聚乙二醇柱和溶胶-凝胶开链冠醚柱已相继制备出来,在用溶胶-凝胶     

Structure Design of Double-Pore Silica and Its Application to HPLC

Utilizing the concurrence of polymerization-induced phase separation and sol-gel transition in the hydrolytic polycondensation of alkoxysilanes, a well-defined macroporous structure is formed in a monolithic wet gel. By exchanging the fluid phase of the wet gel with an appropriate external solution, the nanometer-range structure of the wet gel can be reorganized into structures with larger median pore size essentially without affecting the macroporous framework. The double-pore structure thus prepared is characterized by open pores distributed in discrete size ranges of micrometers and nanometers. A new type of chromatographic column (silica rod) has been developed using monolithic double-pore silica instead of packed spherical gel particles. Typical silica rod columns had significantly reduced pressure drops and improved analytical efficiencies which do not deteriorate even at higher sample flow rates, both arising from a greater macropore volume than particle packed columns.     

Ionic liquids-assisted fabrication of silica-based monolithic columns

The mesopores of a monolithic silica column are very important and useful for chromatographic separation since they can offer sufficiently large surface area. In this paper, a novel method with the assistance of an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate ([bmin]BF₄)) was developed for the preparation of a C18-modified monolithic silica column for the first time, in which, the through pores and mesopores were formed simultaneously during the sol-gel reaction. The method is effective to simplify the preparation process of the silica-based monolithic columns. The factors influencing the sol-gel process, including the content of methanol and pH, were studied. The chromatographic performance of the prepared monolithic column was evaluated by the separation of alkylbenzenes.     

Separation of gold nanoparticles with a monolithic silica capillary column in liquid chromatography

A separation system for gold nanoparticles was developed using monolithic silica capillary columns with 50 μm i.d., which were prepared via in-situ sol-gel processes. Gold nanoparticles with five different average sizes were synthesized via reduction of tetrachloroauric acid (HAuCl(4)) under different synthesis conditions, and were evaluated by UV-visible spectrophotometry, dynamic light scattering as well as transmission electron microscopy before they were separated using the developed system. The results showed that all of the gold nanoparticles had a certain size distribution, and the mean sizes obtained were 13, 17, 33, 43 and 61 nm, with σ = 2.5, 2.7, 5.2, 5.1 and 5.6 nm, respectively. Transmission electron microscopy showed that the samples with mean sizes of 13 and 17 nm were almost spherical, while larger samples were slightly non-uniform. The agglomeration of gold nanoparticles as the sample could be prevented by using a sodium dodecyl sulfate aqueous solution as the mobile phase, and gold nanoparticles were retained by adsorption on the silica surface. Separation with 8 mM sodium dodecyl sulfate as the eluent and a 1000-mm column was successful, and the separation of gold nanoparticles with 61 and 17 nm or 61 and 13 nm was demonstrated. The separation results obtained using a nonporous silica packed column as well as monolithic silica columns with or without mesopore growth were compared. It was found that separation using the mesopore-less monolithic column achieved better resolution. Through the use of a 2000-mm separation column, the mixtures of 61, 43, 17 nm and 61, 33, 13 nm could be separated.     

硅胶整体柱的制备及制备条件对整体柱的影响

研究了硅胶整体柱的制备工艺及温度、pH对凝胶化过程的影响,探讨了不同的四甲氧基硅烷／聚乙二醇比例、不同制也剂浓度对柱结构的影响,以及不同焙烧温度和酸活化处理方法对柱体Si0H含量和线性收缩率的影响,由此确定最佳制备条件。结果表明,采用改进的溶胶-凝胶工艺制备的硅胶整体柱,无开裂变形现象;不同制备条件,可以产生具有不同微米级鞍形骨架、微米级大孔和纳米级中孔的整体柱,可适合不同物质的分离和分析。     

有机-无机杂化硅胶基质整体柱的制备及其电色谱性能

采用溶胶-凝胶法,以四乙氧基硅烷和苯基三乙氧基硅烷作为反应单体,通过酸碱两步催化在毛细管中进行原位缩聚反应,制备了新型有机-无机杂化硅胶基质毛细管整体柱,制备过程简单。整体柱基质中均匀分布的苯基基团可直接用于反相毛细管电色谱的分离,因而不需要对基质再进行衍生化。优化了整体柱的制备条件,采用扫描电镜和压汞法对整体柱的微观结构和孔径分布进行了表征。分别考察了溶胶-凝胶初始反应液中水的用量对柱床结构的影响和两种单体的配比对材料孔径分布的影响。研究了稠环芳烃类化合物在整体柱上的保留行为,用所制备的整体柱分离了7种苯酚类化合物,平均柱效达100000塔板/m。     

Pressurized CEC of neutral and charged solutes using silica monolithic stationary phases functionalized with 3-(2-aminoethylamino)propyl ligands

A novel silica monolithic stationary phase functionalized with 3-(2-aminoethylamino)propyl ligands for pressurized CEC has been presented. The monolithic capillary columns were prepared by a sol-gel process in 75 microm id fused-silica capillaries and followed by a chemical modification. The diamino groups on the surface of the stationary phase are meant to generate the chromatographic surface and a substantial anodic EOF as well as to provide electrostatic interaction sites for charged solutes. The electrochromatographic characterization and column performance were evaluated by a variety of neutral and charged solutes. It was observed that the anodic EOF for the diamine-bonded monolith was greatly affected by the reaction time with 3-(2-aminoethylamino)propyltrimethoxysilane and the PEG amount in the sol-gel reaction mixture in addition to the mobile phase conditions. The monolithic stationary phase exhibited hydrophilic interaction chromatographic behavior toward neutral solutes. Good separations of various solutes including phenols, nucleic acid bases, nucleosides and nucleotides were achieved under different experimental conditions. Fast and efficient separations were obtained with high plate counts reaching more than 130,000 plates/m.     

Facile preparation of organic-inorganic hybrid polymeric ionic liquid monolithic column with a one-pot process for protein separation in capillary electrochromatography

An organic-inorganic hybrid monolithic column based on 1-vinyl-3-dodecylimidazolium bromide (VC₁₂Im⁺Br^?) has been prepared in a single step by combining radical copolymerization with a non-hydrolytic sol-gel (NHSG) process. The NHSG process was significantly shortened to 6 h by using formic acid as catalyst. For comparison, we also prepared polymeric ionic liquid (PIL) monolithic columns by hydrolytic sol-gel and organic polymeric process, respectively. The resulting monolithic columns were characterized by Fourier transform infrared spectra, scanning electron microscopy, and Brunauer-Emmett-Teller. Under the capillary electrochromatography mode, these columns were applied to separate alkylbenzenes, anilines, and proteins, respectively. The results indicated that the NHSG-based hybrid PIL monolithic column exhibited the highest column efficiency among the three types of columns; organic solvent, commonly required by the traditional columns to achieve satisfactory separation efficiency for proteins, was absent in the NHSG-based hybrid PIL monolithic column because of the biocompatibility of the VC₁₂Im⁺Br^?, which was beneficial to analysis of protein containing samples. In order to demonstrate its application potential, the developed NHSG-based hybrid PIL monolithic column was also employed to separate egg white sample.     

Hybrid organic-inorganic phenyl monolithic column for capillary electrochromatography

A novel hybrid organic-inorganic silica-based monolithic column possessing phenyl ligands for reversed-phase (RP) capillary electrochromatography (CEC) is described. The monolithic stationary phase was prepared by in situ co-condensation of tetraethoxysilane (TEOS) with phenyltriethoxysilane (PTES) via a two-step catalytic sol-gel procedure to introduce phenyl groups distributed throughout the silica matrix for chromatographic interaction. The hydrolysis and condensation reactions of precursors were chemically controlled through pH variation by adding hydrochloric acid and dodecylamine, respectively. The structural property of the monolithic column can be easily tailored through adjusting the composition of starting sol solution. The effect of PTES/TEOS ratios on the morphology of the created stationary phases was investigated. A variety of neutral and basic analytes were used to evaluate the column performance. The CEC columns exhibited typical RP chromatographic retention mechanism for neutral compounds and had improved peak shape for basic solutes.     

Preparation of high efficiency and highly retentive monolithic silica capillary columns for reversed-phase chromatography by chemical modification by polymerization of octadecyl methacrylate

High efficiency and highly retentive monolithic silica capillary columns were obtained by polymerization of octadecyl methacrylate using alpha,alpha'-azobis-isobutyronitrile (AIBN) as a free radical initiator. Hybrid type monolithic silica columns (25 cm total length x 200 microm I.D.) prepared from a mixture of tetramethoxysilane and methyltrimethoxysilane were used as a support. The effects of the monomer and the radical initiator concentrations in the reaction mixture were examined. The performance of the columns was tested in terms of column efficiency and retention behavior by using alkylbenzenes and a few other compounds as solutes and compared with that of hybrid monolithic silica columns modified with octadecylsilyl-(N,N-diethylamino)silane (ODS-DEA). Highly retentive monolithic silica columns were obtained by polymerization at high monomer concentrations. Although a decrease in column efficiency was observed with the increase in the monomer concentration in a feed mixture, an improvement in efficiency was achieved (a plate height value lower than 10 microm) by increasing an initiator concentration without significant variations in column retention properties. Results obtained by polymerization using other monomers are also presented to demonstrate the applicability of the preparation method.     

丁基胺丙基硅胶毛细管整体柱的制备及其电色谱性能研究

采用溶胶-凝胶技术制备了丁基胺丙基硅胶毛细管整体柱,此整体固定相表面同时含有能产生阳极的电渗流的仲胺官能团和产生疏水作用的正丁基和丙基官能团。对所制备的整体柱电色谱性能进行了详细的表征和分析。考察了流动相pH值对电渗流的影响;对烷基苯同系物、有机酸酸性化合物和苯胺类碱性化合物保留行为进行了研究,并对其可能的保留机理进行了探讨。实验结果表明,对于中性化合物的保留机理主要基于反相作用;而对于酸性化合物的保留行为则是基于混合模式作用机理,即除了电泳作用外,还包括阴离子交换和疏水作用。碱性化合物在丁基胺丙基硅胶毛细管整体柱上的峰形较好,没有明显的峰拖尾现象。     

Development of a new C14 monolithic silica column containing embedded polar groups for pressurized capillary electrochromatography

Monolithic columns have been prepared with a novel bonded silica stationary phase, tetradecylamine bonded silica (TDAS), and used in pressurized capillary electrochromatography (pCEC). The monolithic silica column matrix was prepared by a sol-gel process and then chemically modified with the spacer (3-glycidoxypropyl)trimethoxysilane and tetradecylamine. The introduced embedded polar amine groups dominated the charge on the surface of the monolithic stationary phase and generated an EOF from cathode to anode under acidic conditions. The tetradecyl hydrophobic chains in TDAS provide chromatographic interactions. The chromatographic characteristics of the prepared monolithic column were studied. Some aromatic compounds including alkylbenzenes, aromatic hydrocarbons, phenols, and anilines were successfully separated on the TDAS monolithic column in pCEC mode. As expected, the TDAS monolithic stationary phases exhibit typical reversed-phase electrochromatographic behavior toward neutral solutes due to the introduced tetradecyl groups. Hydrophobic as well as electrophoretic migration processes within the monoliths were observed in the separation of basic anilines. Symmetrical peaks can be obtained for anilines because the embedded polar amine groups on the surface can effectively shield the adsorption of positively charged analytes onto the stationary phase.     

Study of triacontyl-functionalized monolithic silica capillary column for reversed-phase capillary liquid chromatography

A novel stationary phase triacontyl-functionalized monolithic silica capillary column was successfully prepared for reversed-phase capillary liquid chromatography. The performance of the monolithic silica capillary column coated with triacontyl chain for the separation of alkylbenzenes, xylene isomers, polycyclic aromatic hydrocarbons, and mixture of α- and β-carotenes was studied, which was compared to that using the monolithic silica capillary column coated with octadecyl chain. The comparison results showed that triacontyl-functionalized monolithic silica capillary column would be a promising media to be used for the separation of isomeric solutes with long chain in reversed-phase capillary liquid chromatography.     

硅胶整体柱芯的制备方法研究

目前,新型色谱填充材料发展很快,但传统的高效液相色谱(HPLC)颗粒型填充柱存在缺陷,难以实现既高效又快速的分离,Minakuchi等制备了连续的硅胶整体柱,该柱同时具有通孔和中孔双孔结构,孔容量大大高于填充柱,因此,该柱具有高速、低压、高效、适于溶剂及流速梯度洗脱等优点,适合高通量分析和快速分离,     

应用于全氟辛烷磺酸萃取富集的全氟癸基修饰毛细管硅胶整体柱的制备及应用

利用溶胶-凝胶法,经过烷氧基硅烷的水解、硅羟基的缩聚、凝胶化、陈化、中孔制备、干燥和表面修饰等步骤制备了全氟癸基修饰的毛细管硅胶整体柱。采用该整体柱对全氟辛烷磺酸(PFOS)进行萃取富集,考察其富集特性和效率,并与传统的C18毛细管硅胶整体柱进行对比。结果表明,全氟癸基修饰毛细管硅胶整体柱(15 cm×75 μm)对PFOS具有更高的吸附量和更好的富集选择性,其平均吸附量可以达到75 ng;样品中PFOS的质量浓度为0.25 mg/L时,富集倍数平均可以达到29倍。此全氟癸基修饰毛细管硅胶整体柱对PFOS具有良好的萃取富集性能,可用于水质中痕量PFOS的萃取富集。