反相毛细管电色谱中中性化合物的保留及有机改性剂对其保留值的影响

以硫脲作为电渗流标记物测定的死时间和以苯同系物线性回归方法测定的死时间为基础，将液相色谱中溶质保留值方程应用到电色谱中，得到了容量因子与二元流动相体系中有机改性剂含量之间的关系曲线；通过实验数据说明了一些极性的电中性化合物在电场作用下也会发生迁移而引起保留值的变化，且这种变化还受有机改性剂含量的影响。     

反相液相中lgI对极性小分子溶质行为的表征

 以极性溶质正链醇同系物及芳香醇同系物的实验数据对反相液相中计量置换表征参数lgI进行了多方面验证 ,并将lgI值与溶质的其他物理化学参数做了比较 ,证明了lgI在限定条件下分别可作为溶质的种类和大小、流动相中置换剂、所选用固定相特性及有关溶质分离选择性大小的表征参数 ,也证明了极性溶质体系的lgI亦具有热力学平衡常数的性质。     

混合固定相电中溶质的输运特征

 以离子交换和反相固定相构成的混合固定相电中 ,溶质迁移在受到疏水、离子交换作用的同时 ,对于带电溶质而言 ,还受到电泳迁移的影响。根据离子独立迁移原理 ,结合过程中的多种相互作用 ,得到了描述溶质表观迁移速率与其各形态迁移速率、各种相互作用之间相互关系的理论表达式 ;讨论了混合模式电中流动相的 pH及其中的有机调节剂浓度、混合固定相配比等对电渗流的影响及不同形态溶质在柱内的输运特征。结果表明 ,在电中采用混合固定相可以在较大的 pH和有机调节剂浓度范围内得到较强且稳定的电渗流。     

聚丙烯酸酯类毛细管整体柱的制备及其在加压毛细管电色谱中的应用

毛细管电色谱(CEC)是毛细管电泳(CE)和微径液相色谱(micro—HPLC)技术的结合,是集CE的电子迁移机制和micro-HPLC的分配分离机理发展起来的一种高效微分离技术．CEC以塞子流型的电渗流代替抛物线流型的压力流,具有CE的高效性,能够分离电中性化合物而具有HPLC的高选择性．     

磷脂微乳电动色谱的定量结构保留关系研究

以大豆磷脂为主要的表面活性剂,制备适合毛细管电动色谱使用的不同构成比的微乳体系, 应用溶剂化参数模型研究了中性溶质在其中的定量结构保留关系.使用动态涂层毛细管, 以二甲基亚砜和十二烷基苯分别作为电渗流和微乳液滴迁移的标记物, 测定了26个具有不同结构小分子中性化合物在17种微乳电动色谱体系下的保留因子, 建立了线性溶剂化能量关系(LSER)方程.通过比较两体系的LSER方程系数比较体系相似性.结果表明, 本研究建立的磷脂微乳电动色谱体系在线性溶剂化特征上和其它构成的微乳电动色谱体系相似.对溶质保留贡献较大的是溶质体积和有效氢键碱度, 油相种类及浓度对溶质的保留选择性无明显影响.     

新型反相毛细管硅胶电色谱整体柱的制备

色谱柱是色谱分离的核心,其性能的不断改进对色谱技术的发展极其重要.毛细管电色谱既作为固定相承担分离任务,又产生电渗流,作为驱动力带动溶质的迁移.     

应用四甲基氢氧化铵控制电渗流的毛细管电泳方法分离多沙唑嗪及其中间体的对映体

建立了毛细管电泳手性分离多沙唑嗪中间体对映体的方法,并同时分离了多沙唑嗪对映体。考察了不同种类季铵盐对电渗流及分离的影响,其中四甲基氢氧化铵(TMB)能有效控制电渗流并提高组分的分离度。实验还考察了其他因素,如pH值、分离电压和磷酸二氢钠浓度对分离的影响。所用的毛细管为40 cm(有效长度30 cm)×50 μm,缓冲液为12 mmol/L β-环糊精、30 mmol/L TMB、60 mmol/L 磷酸二氢钠(pH 2.2),分离电压为20 kV。在此条件下多沙唑嗪及其中间体的对映体均达到了基线分离。实验结果表明,一些用β-环糊精不能完全分离的对映体通过加入TMB控制电渗流能达到满意的分离效果。     

聚合离子液体用作毛细管电泳背景电解质添加剂快速高效分离5种核苷类化合物

将聚乙烯基-3-乙基咪唑溴盐离子液体用作毛细管电泳背景电解质添加剂,利用聚合离子液体的阳离子聚合物性质静电吸附到毛细管内表面,成功实现电渗流的有效反转,建立了共电渗流模式下5种核苷类化合物分离的新方法。考察了聚合离子液体浓度、pH值等因素对电渗流的影响。在优化实验条件下,3.1 min内实现了对5种核苷类化合物的快速高效分离;将该方法分别与不加添加剂和加入离子液体单体后的体系进行对比,结果表明,该方法大大缩短了5种核苷类化合物的分析时间,提高了分析效率,最高柱效达95万/m塔板数,分析物的迁移时间RSD均不高于0.38%。该方法简单、快速、重复性好,具有很好的应用前景。     

芳香化合物在氰基键合填充柱上的电色谱保留行为

在３μｍ氰基键合固定相上实施毛细管电色谱,采用乙腈／Ｔｒｉｓ反相洗脱,在７５μｍｉ．ｄ．×２５ｃｍ的毛细管柱上分离了几种芳香化合物,并对其保留行为进行了研究。利用溶剂特征显色比较法对溶质的保留进行了预测。同时还研究了乙腈的比例对电渗流的影响。对于不保留的溶质,获得了小于２．０的折合塔板数。     

氨基安替比林MIP-CEC整体柱的制备及电色谱性能研究

以氨基安替比林为模板分子,在内径100 μm的石英毛细管内采用原位聚合法制备了分子印迹毛细管整体柱,以电色谱模式分离了氨基安替比林及其结构类似物安替比林,在乙腈(体积分数15%)-磷酸二氢钠缓冲液(5 mmol/L)作为流动相(pH 7.0)条件下,18 min内完成分离,分离因子为1.37.考察了缓冲液中乙腈含量、pH值、离子强度对电渗流、溶质保留时间及分离因子的影响,探讨了整体柱识别机理.     

硅胶电色谱分离机理的研究

对硅胶电色谱柱的性能进行了考察,发现在水／有机溶剂流动相条件下,几乎不存在气泡问题,流动相的组成在有机溶剂浓度、电解质浓度、ＰＨ值等方面可以在较大范围变化,选用５种典型样品,对硅胶电色谱的分离机理进行了系统研究,发现有反相分离机理、正相吸附机理、离子交换机理以及电泳机理参与作用。同时考察了有机溶剂浓度、电解质浓度、ＰＨ等对分离的影响。此外,还首次提出了一种全新的电色谱模式－动态改性硅胶电色谱。     

毛细管反相电色谱法分离行为的研究

对乙睛-水-磷酸二氢销体系毛细管反相电色谱分离行为进行了研究。采用柱上紫外检测,在75μmi.d.×30cm的毛细管ODS（3μm）填充柱上获得了小于2.0的折合培板高度。同时还研究了乙睛的比例、电解质的浓度和电场强度等因素对电渗流和往效的影响。     

Influence of mobile phase composition on electroosmotic flow velocity, solute retention and column efficiency in open-tubular reversed-phase capillary electrochromatography

The effects of some experimental parameters, such as the volume fraction and type of organic modifier in the mobile phase, and the concentration, type and pH of the buffer on the electroosmotic flow velocity, the retention behavior of test solutes, and the column efficiency have been investigated in capillary electrochromatography (CEC) using an open-tubular column of 9.60 microm I.D. with a porous silica layer chemically modified with C18 as stationary phase. The retention of a group of polycyclic aromatic hydrocarbons (PAHs) used as a test mixture varied significantly by changing the organic modifier content in the hydroorganic mobile phase according to the reversed-phase-like selectivity of the stationary phase. In addition, an increase in the percentage of organic modifier resulted in a slight increase in the linear velocity of the EOF. On the other hand, when the phosphate buffer concentration was increased over the range 1-50 mM, the electroosmotic mobility fell dramatically, the retention of the solutes decreased steadily, and the plate height showed a significant increase. The results obtained with phosphate, trishydroxymethylaminomethane or 2-morpholinoethanesulfonic acid as buffers were similar when pH remained constant. Optimization in CEC was essential to achieve further enhancement of separation performance, because the analysis time and separation resolution are essentially affected when varying operating parameters. Separations of seven PAHs with more than 100000 plates are presented within 4 min analysis time.     

Separation of theophylline, caffeine and related drugs by normal-phase capillary electrochromatography.

A capillary electrochromatography (CEC) method has been developed for the separation of theophylline, caffeine and five related drugs on a normal-phase column with UV or photodiode array detection. Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable organic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris (52:40:8, pH 8), with an efficiency of 63000 theoretical plates per meter at room temperature. Detection limits are typically at the low microg/mL level. The developed method is simple to use and it gives acceptable day-to-day reproducibility.     

Capillary Electrochromatography on Methacrylate Based Monolithic Columns: Evaluation of Column Performance and Separation of Polyphenols

Fused-silica capillary columns (100 μm I.D.) englobing a porous monolithic stationary phase were prepared by in situ copolymerization of 2-ethylhexyl methacrylate, ethylene glycol dimethacrylate and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in the presence of a porogenic mixture containing 1-propanol, 1,4 butanediol and water. The influence of the monomers ratio and the porogen solvent composition as well as the content of AMPS in the polymerization mixture on column total porosity and efficiency was investigated to attain minimum HETP values for the reversed-phase capillary electrochromatography separation of bioflavonoids. For the most promising column, the van Deemter plots, in both μ-HPLC and CEC, were also evaluated. In CEC the reduced plate height was found almost constant (1.6–2.0) within the range of linear mobile phase velocity between 0.2–2.0 mm s⁻¹. The chemical and mechanical stabilities of the monolithic column over a wide range of buffer pH (2-10) and time were satisfactory. Furthermore, the effects of mobile phase parameters, such as buffer concentration and organic modifier content, on the electroosmotic flow were studied systematically. CEC separations of standard mixtures of polyphenols, including flavonols, flavanones and flavanones-7-O-glycosides, were accomplished in less than 8 min. The CEC separation of the major flavanone glycoside constituents in the extract from a freshly squeezed grapefruit juice was also reported.     

On-line concentration and pressurized capillary electrochromatographic analysis of phytohormones in corn

A pressurized CEC (pCEC) method was developed for the separation of phytohormones, in which UV absorbance was used as the detector and a monolithic silica-ODS column as the separation column. The parameters (including the concentration of organic solvent in the mobile phase, pH of the electrolyte buffer, applied voltage) affecting the separation resolution were evaluated. Two on-line concentration techniques, namely, solvent gradient zone sharpening effect and field-enhanced sample stacking, were utilized to improve detection sensitivity. The combination of the two techniques proved to be beneficial to enhance the detection sensitivity by enabling the injection of large volumes of samples. Compared to the conventional injection mode, the enhancement in the detection sensitivities of phytohormones using the on-line concentration technique is in the range from 9- to 23-fold. The developed pCEC method was applied to evaluate phytohormones in corns.     

Separation of parabens in capillary electrochromatography using poly(styrene-divinylbenzene-methacrylic acid) monolithic column

In this study, a series of poly(styrene-divinylbenzene-methacrylic acid) monolithic capillaries was used as the separation column of CEC for the analyses of parabens in commercial pharmaceutical and cosmetic products. The results showed that the chromatographic characteristics of these analytes were strongly affected by the preparation condition of the monolithic column including monomer content, porogenic solvent composition, and polymerization time. Baseline separations were markedly sped up by lowering the polymerization time without any obvious loss of resolution. Furthermore, mobile-phase composition (pH, ACN, and electrolyte concentration) was also able to effectively improve the separation behavior. Similar to the influence of lowering the polymerization time, retention times for all analytes were significantly shortened in the CEC method by decreasing the electrolyte concentration in the mobile phase.     

Use of on-line mass spectrometric detection in capillary electrochromatography

Capillary electrochromatography (CEC) is a liquid phase analytical separation technique that is generally carried out with packed capillary columns by electroosmotically driven mobile phase at high electric field strength. The analytes are separated by virtue of the differences in their distribution between the mobile and stationary phases and, if charged in their electrophoretic mobilities as well. It is thus considered a hybrid of liquid chromatography and capillary electrophoresis and is expected to combine the high peak efficiency of capillary zone electrophoresis (CZE) with the versatility and loading capacity of HPLC. This review explores the potential use of on-line mass spectrometric detection for CEC. It discusses key design issues that focus on the physical and electrical arrangement of the CEC column with respect to the electrospray orifice inlet. The salient features of the sheathless, sheath flow and liquid junction interfaces that are frequently employed while coupling a CEC column to an electrospray ionization mass spectrometry system are also highlighted. Possible configurations of the CEC column outlet that would obviate the need for pressurizing the capillary column are also presented. While coupling CEC with MS both the nature of the interface and the configuration of the column outlet will determine the optimal arrangement. The review also discusses bandspreading that occurs when a connecting tube is employed to transfer mobile phase from the column outlet to the atmospheric region of the electrospray source with a concomitant loss in sensitivity. Selected examples that highlight the potential of this technique for a wide range of applications are also presented.     

Peak shapes in open tubular ion-exchange capillary electrochromatography of inorganic anions

An experimental study of parameters influencing peak shapes in ion-exchange open tubular (OT) capillary electrochromatography (CEC) was conducted using adsorbed quaternary aminated latex particles as the stationary phase. The combination of separation mechanisms from both capillary electrophoresis and ion-exchange chromatography results in peak broadening in OT-CEC arising from both these techniques. The sources of peak broadening that were considered included the relative electrophoretic mobilities of the eluent co-ion and analyte, and resistance to mass transfer in both the mobile and stationary phases. The parameters investigated were the mobility of the eluent co-ion, column diameter, separation temperature and secondary interactions between the analyte and the stationary phase. The electromigration dispersion was found to influence peak shapes to a minor extent, indicating that chromatographic retention was the dominant source of dispersion. Improving the resistance to mass transfer in the mobile phase by decreasing the capillary diameter improved peak shapes, with symmetrical peaks being obtained in a 25 microm I.D. column. However, an increase in temperature from 25 degrees C to 55 degrees C failed to show any significant improvement. The addition of p-cyanophenol to the mobile phase to suppress secondary interactions with the stationary phase did not result in the expected improvement in efficiency.     

Electrochromatographic performance of conventional and polar-embedded C16 silica monolithic stationary phases

A novel monolithic silica column that has a polar‐embedded amide‐secondary amine group linking with C16 functionality for RP‐CEC is described. The amide‐secondary aminealkyloxysilane was synthesized by the reaction of 3‐(2‐aminoethylamino) propyltrimethoxysilane with hexadecanoyl chloride. Then, the silylant agent was bonded to the silica monolith matrix to produce hexadecanamide‐secondary amine bonded silica (HDAIS) monolithic column. The electrochromatographic performance of HDAIS monolithic column for the separation of neutral, basic and polar solutes was studied, which was compared to that using the hexadecyl bonded silica monolithic column. The HDAIS monolithic column displayed reduced hydrophobic retention characteristics in the separation of five hydrophobic n‐alkylbenzenes and four polar phenols when compared to the hexadecyl bonded silica monolithic column. A very much reduced silanol activity of HDAIS monolithic column was observed in the separation of test basic mixture including four aromatic amines, atenolol and metoprolol with 10 mM borate buffer (pH 7.5) containing 30% v/v ACN as the mobile phase. The comparison results indicate good performance for both polar and basic mixtures on HDAIS monolithic column in RP‐CEC, and also show promising results for further applications.