Preparation of low flow-resistant methacrylate-based monolithic stationary phases of different hydrophobicity and the application to rapid reversed-phase liquid chromatographic separation of alkylbenzenes at high flow rate and elevated temperature

Low flow-resistant alkyl methacrylate-based monolithic stationary phases of different hydrophobicity were constructed for reversed-phase capillary liquid chromatography by thermally initiated radical polymerization of respective methacrylate ester monomer with different alkyl chain (C2, C4, C6, C12, C18) and ethylene glycol dimethacrylate (EDMA) in a 250 microm i.d. fused silica capillary. The hydrophobicity was basically controlled by changing the length and/or the density of the alkyl-chain, while the composition and the ratio of porogenic solvent were adjusted to obtain highly permeable rigid monoliths with adequate column efficiency. Among the prepared monolithic stationary phases, C18-methacrylate monoliths polymerized from a binary porogenic solvent of isoamyl alcohol and 1,4-buthandiol exhibited the most promising performance in terms of hydraulic resistance and column efficiency. The pressure drops of 20-cm long monolithic columns were below approximately 0.4 MPa at a normal linear velocity of 1mm/s (a flow rate of 3 microL/min), and the numbers of theoretical plates for alkylbenzenes mostly exceeded 3000 plates/20 cm. The produced monolithic columns had good mechanical strength for high pressure and temperature, and could be properly operated even at a temperature of 80 degrees C and at a pressure of at least 33 MPa. At 80 degrees C, the theoretical plate numbers reached 6000 plates/20 cm because of the enhanced mass transfer. Due to the novel hydraulic resistance and mechanical strength, the separation time could be reduced 120-fold simply by raising the flow rate and column temperature.     

正交试验法优化制备用于小分子物质分离的聚(甲基丙烯酸缩水甘油酯-二乙烯基苯)型整体柱

以甲基丙烯酸缩水甘油酯(GMA)为单体,二乙烯基苯(DVB)为交联剂,以环己醇和正十二醇为致孔剂,过氧化苯甲酰(BPO)为引发剂,直接以50 mm×4.6 mm色谱柱为模具,通过原位聚合制备聚(GMA-DVB)型整体柱。以GMA和DVB的体积比、环己醇和十二醇的体积比以及BPO占聚合物的质量分数为三因素,以分离苯和乙苯等小分子物质时的半峰宽分离度(R1/2)为考察指标,进行三因素三水平的正交试验,通过测定整体柱的比表面积、孔径和孔容分布对其进行表征。结果表明,制备整体柱的最优配方为V(GMA): V(DVB): V(环己醇): V(正十二醇)=0.825:0.825:1.32:2.03, BPO的质量分数为0.7%。应用所制备的整体柱分离苯和乙苯等小分子物质,理论塔板数达到37000塔板/m, R1/2值达到7.14,完全达到基线分离,分离时间小于10 min。该方法制备整体柱的重复性好,柱效较高,基本满足商品化要求。     

Size separation of colloidally dispersed nanoparticles using a monolithic capillary column

We developed a method to separate colloidally dispersed nanoparticles on monolithic capillary columns. Silica nanoparticles were eluted according to their sizes, and the plots of the logarithm of the size of nanoparticles against their elution volume showed good linearity (r=0.992) over wide range of sizes. Because of the high porosity of the monolithic column (porosity; 88%), the column's length could be increased without clogging of the dispersed samples and the pressure in a long column (500 mm × 0.2 mm i.d.) was low, with a value of 5.8 MPa at a flow rate of 1 μL/min. We demonstrate that this method using monolithic capillary columns could be used as a powerful tool for size separation of nanometer-size materials, which will open a new pathway to quality control of nanomaterials in nanotechnology applications.     

Preparation and evaluation of poly(alkyl methacrylate-co-methacrylic acid-co-ethylene dimethacrylate) monolithic columns for separating polar small molecules by capillary liquid chromatography

In this study, methacrylic acid (MAA) was incorporated with alkyl methacrylates to increase the hydrophilicity of the synthesized ethylene dimethacrylate-based (EDMA-based) monoliths for separating polar small molecules by capillary LC analysis. Different alkyl methacrylate–MAA ratios were investigated to prepare a series of 30% alkyl methacrylate–MAA–EDMA monoliths in fused-silica capillaries (250-μm i.d.). The porosity, permeability, and column efficiency of the synthesized MAA-incorporated monolithic columns were characterized. A mixture of phenol derivatives is employed to evaluate the applicability of using the prepared monolithic columns for separating small molecules. Fast separation of six phenol derivatives was achieved in 5 min with gradient elution using the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column. In addition, the effect of acetonitrile content in mobile phase on retention factor and plate height as well as the plate height-flow velocity curves were also investigated to further examine the performance of the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column. Moreover, the applicability of prepared polymer-based monolithic column for potential food safety applications was also demonstrated by analyzing five aflatoxins and three phenicol antibiotics using the selected poly(lauryl methacrylate-co-MAA-co-EDMA) monolithic column.     

Preparation and characterization of methacrylate-based semi-micro monoliths for high-throughput bioanalysis

Hexyl methacrylate (HMA)-based monolithic semi-micro columns were prepared by in situ polymerization within the confines of 1.02-mm-i.d. silicosteel tubing for reversed-phase and/or precipitation–redissolution liquid chromatography. Practically useful monolithic columns with adequate separation efficiency, high permeability, and good mechanical strength were successfully obtained using a polymerization mixture comprising 24% hexyl methacrylate (HMA), 6% ethylene dimethacrylate (EDMA), 44.5% 1-propanol, and 25.5% 1,4-butanediol. The column performance was evaluated through the separations of a series of alkylbenzenes. At a normal flow rate of 50 μL min⁻¹, the produced HMA-based monolithic columns typically exhibited 3,000 theoretical plates for a 20-cm-long column, and the pressure drop was generally less than 1 MPa per 20 cm. The monolithic columns were resistant to at least 15 MPa, and could be properly operated at 15–20 times higher flow rate than normal, reducing the separation time to 1/15–1/20. The HMA-based monolithic columns were applied to rapid and efficient separations of proteins such as ribonuclease A, cytochrome c, transferrin, and ovalbumin in the precipitation–redissolution mode. Using a CH₃CN gradient elution at a flow rate of 1,000 μL min⁻¹, four proteins were baseline separated within 20 s.     

New vinylester‐based monoliths as a new stationary phase for capillary electrochromatography

Vinyl ester‐based monoliths are proposed as a new group of stationary phase for CEC. The capillary monolithic columns were prepared by using two vinyl ester monomers, vinyl pivalate (VPV), and vinyl decanoate (VDC) by using ethylene dimethacrylate (EDMA) as the cross‐linking agent, and 2‐acrylamido‐2‐methylpropane sulfonic acid as the charge‐bearing monomer. The monoliths with different pore structures and permeabilities were obtained by varying the type and composition of the porogen mixture containing isoamyl alcohol and 1,4‐butanediol. The electrochromatographic separation of alkylbenzenes was successfully performed by using an acetonitrile/aqueous buffer system as the mobile phase in a CEC system. Vinyl ester monoliths with short alkyl chain length (i.e. poly(VPV‐co‐EDMA) exhibited better separation performance compared with the monolith with long alkyl chain length (i.e. poly(VDC‐co‐EDMA). In the case of VPV‐based monoliths, the theoretical plate numbers higher than 250 000 plates/m were achieved by using a porogen mixture containing 33% v/v of isoamyl alcohol. For both VDC and VPV‐based monoliths, the column efficiency was almost independent of the superficial velocity in the range of 2–12 cm/min.     

反相毛细管整体柱的制备及其在多肽混合物分离中的应用

采用甲基丙烯酸月桂酯为基础功能单体,乙二醇二甲基丙烯酸酯为交联剂,正十二醇、1,4-丁二醇及二甲基亚砜为致孔剂,在内径为75 μm的石英毛细管内制备了具有良好机械性能及化学稳定性的反相毛细管整体柱。考察了致孔剂的种类、比例以及交联剂在单体混合物中的比例对柱压和分离效果的影响;以单体15%、交联剂15%、致孔剂70%(均为质量分数)作为优化配方,在70 ℃条件下反应24 h;并对所合成的毛细管整体柱进行了电镜表征,测试了流速、柱长与柱压的关系。结果表明,毛细管整体柱的通透性良好,可通过延长柱长的方法提高分离效果。将所制备的毛细管整体柱装于纳升级高效液相色谱仪上进行牛血清白蛋白及血浆样本的胰蛋白酶酶切液的分离,获得了比较理想的分离效果。     

聚十二烷基甲基丙烯酸酯整体柱的制备及其在毛细管电色谱法分离肌红蛋白酶解产物中的应用

以十二烷基甲基丙烯酸酯(LMA)为功能单体,乙叉二甲基丙烯酸酯(EDMA)为交联剂,正丙醇、1,4-丁二醇和水为三元致孔剂,以及2-丙烯酰胺-2-甲基丙磺酸(AMPS)为电渗流产生剂,制备了聚十二烷基甲基丙烯酸酯整体柱。系统考察了AMPS含量和单体-致孔剂比例对柱性能的影响。结果表明,单体溶液和致孔剂的最佳聚合溶液质量比为35:65,其中单体溶液组成为59.5%（质量分数,下同）LMA、40%EDMA和0.5%AMPS,致孔剂溶液组成为60%正丙醇、30%1,4-丁二醇和10%水。在优化的流动相条件下应用制备的整体柱采用毛细管电色谱法成功地分离了肌红蛋白酶解产物。     

整体柱在线固相微萃取-高效液相色谱法分析爽肤水中痕量雌激素

以甲基丙烯酸缩水甘油酯(GMA)为功能单体、乙二醇二甲基丙烯酸酯(EDMA)为交联剂,偶氮二异丁腈(AIBN)为引发剂、甲醇及正己烷(14∶5,v/v)为二元致孔剂,通过原位聚合反应制备了聚甲基丙烯酸缩水甘油酯(Poly(GMA-co-EDMA))毛细管整体柱。研究表明,制备的Poly(GMA-co-EDMA)整体柱具有良好的通透性和较低的柱压(1.5×106Pa,冲洗流速0.5 mL/min)。该整体柱对雌二醇、炔雌醇、雌酮和己烯雌酚的富集倍数分别为86、116、77和86。构建了整体柱在线微萃取接口装置,建立了整体柱在线固相微萃取-高效液相色谱(HPLC)测定爽肤水中痕量雌二醇、炔雌醇、雌酮和己烯雌酚的分析方法。该分析方法的检出限(S/N=3)为0.05~0.20μg/L。将方法应用于爽肤水中雌激素的检测,加标回收率为69.3%~111.3%,RSD5.0%。所建立的方法简单、快速、灵敏、准确,可满足爽肤水中痕量雌激素的分析。     

弱阳离子交换整体柱的制备及其对人血浆中硝苯地平的在线分析

以甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EDMA)为交联剂,以色谱柱管为模具,通过原位聚合法制备了弱阳离子交换整体柱。该柱能去除血浆中的内源性物质,对生物样品中的药物有富集作用。将其作为固相萃取柱与C18色谱柱联用,在线分析了人血浆中的硝苯地平。流动相为甲醇-水(体积比为70∶30),流速1.0 mL/min,检测波长235 nm。结果表明,硝苯地平在5.0～75.0 μg/L范围内线性关系良好(r=0.9993),方法的回收率为90.0%～99.0%,日内、日间相对标准偏差均小于5.0%。该方法精密度高,重现性良好,避免了繁琐的样品预处理过程,且弱离子整体柱可多次重复使用,为检测血浆中的痕量药物提供了一种快速、经济、有效的新方法。     

Novel separation medium spongy monolith for high throughput analyses

Sponge-like material was utilized as novel chromatographic media for high throughput analyses. The pore size of the sponge-like material was several dozen micrometer, and was named spongy monolith because it consists of continuous structured copolymers, which was made of poly(ethylene-co-vinyl acetate), such as monolithic materials including silica monoliths and organic polymer monoliths. The spongy monolith was packed into a stainless steel column (100 mm × 4.6 mm I.D.) and evaluated in liquid chromatography (LC) with an on-line column-switching LC concentration system. The results indicate that the packed column could be used with high flow rates and low back pressure (9.0 mL/min at 0.5 MPa). Furthermore, bisphenol A was quantitatively recovered by on-line column-switching LC concentration with the spongy monolithic column. Additionally, the adsorption capacity and physical strength of the media was enhanced via chemical modification of spongy monoliths using glycerol dimethacrylate. The results compared with original spongy monolith demonstrated that a higher adsorption capacity was achieved on a shorter column, and a stable low back pressure was obtained at high throughput elution even with a longer column.     

Development and validation of a rapid HPLC method for the determination of five banned fat-soluble colorants in spices using a narrow-bore monolithic column

This work reports a fast and simple liquid chromatographic method for the simultaneous determination of five banned fat-soluble synthetic colorants, namely Sudan I-IV and Para-Red, in spice samples. The analytes were successfully separated isocratically in less than 5 min on the new narrow bore monolithic column, FastGradient^® Chromolith (50 mm × 2.0 mm i.d.) using a mobile phase of 0.1% (v/v) HCOOH/acetonitrile (35/65%, v/v) at a flow rate of 1.5 mL min⁻¹. All colorants were detected at 506 nm. The main parameters (mobile phase composition, flow rate, injection volume) affecting the separation were studied. The proposed method was thoroughly validated in terms of linearity, LODs, precision and accuracy. The method was applied to the determination of the studied azo-dyes in various spices (paprika, chilli and mixed spice powders) after ultrasound-assisted extraction. Satisfactory recoveries, ranging from 92% to 109% were obtained.     

混合模式毛细管聚合物整体柱的制备及应用

混合模式毛细管整体色谱柱由于保留机理多样,具有很好的应用前景。本文以[2-（甲基丙烯酰基氧基）乙基]二甲基-（3-磺酸丙基）氢氧化铵（SPE）为单体,乙二醇二甲基丙烯酸酯（EDMA）为交联剂,偶氮二异丁腈（AIBN）为引发剂,正丙醇/1,4-丁二醇/水三元体系为致孔剂,制备了聚合物基质SPE-co-EDMA毛细管液相色谱整体柱。通过系统优化致孔剂和反应物种类和配比、引发剂的用量、反应时间和反应温度等因素,提高了整体柱的柱效、机械强度、渗透性和重复性。结果表明该毛细管整体柱在10 MPa内具有良好的机械强度,渗透性为2.17×10^-14 m²,而且批次内和批次间峰面积的重现性（RSD）分别为1.0%和4.6%。以极性和非极性的多种化合物评价了该毛细管整体柱的色谱性能,结果表明该柱在高有机相中具有亲水相互作用机理,在低有机相中具有反相作用机理,显示出混合模式分离特性。     

阴离子交换整体柱对蛋白质的分离与纯化

分别用乙二胺、二乙胺、三乙胺将自制的以甲基丙烯酸缩水甘油酯(GMA)为单体、乙二醇二甲基丙烯酸酯(EDMA)为交联剂的整体柱修饰为弱、强阴离子交换整体柱。考察了该整体柱的性能,选择出分离蛋白质(牛血清白蛋白、溶菌酶和谷胱甘肽)的最佳实验条件,并在最佳分离条件下考察了这些蛋白质在整体柱上的色谱行为和该整体柱对纤维素降解酶的分离纯化情况。实验结果表明,该整体柱性能良好,可以实现对纤维素降解酶的快速分离与纯化。同时,实验也证明采用梯度洗脱可以实现对某些蛋白质的分离纯化。     

Polyhedral oligomeric silsesquioxanes as functional monomer to prepare hybrid monolithic columns for capillary electrochromatography and capillary liquid chromatography

A simple approach to fabricate hybrid monolithic column within the confines of fused-silica capillaries (75 μm i.d.) was introduced. A polyhedral oligomeric silsesquioxanes (POSS) reagent containing a methacrylate group was selected as functional monomer, and copolymerized with bisphenol A dimethacrylate (BPADMA) or ethylene dimethacrylate (EDMA) in the presence of porogenic solvents via thermally initiated free radical polymerization. After optimization of the preparation conditions, two POSS-containing hybrid monoliths were successfully prepared and exhibited good permeability and stability. By comparison of the separation efficiencies of the resulting poly(POSS-co-BPADMA) and poly(POSS-co-EDMA) monoliths in capillary electrochromatography (CEC) and capillary liquid chromatography (cLC), it was indicated the former has better column efficiencies for alkylbenzenes, phenols, anilines and PAHs in CEC and cLC than the latter. Particularly, the hybrid poly(POSS-co-BPADMA) monolith is more suitable for separation of PAHs due to π–π interaction between the analytes and aromatic rings in the surface of monolithic stationary phase.     

Preparation of monoliths from single crosslinking monomers for reversed-phase capillary chromatography of small molecules

Highly cross-linked networks resulting from single crosslinking monomers were found to enhance the concentrations of mesopores in, and the surface areas of, polymeric monoliths. Four crosslinking monomers, i.e., bisphenol A dimethacrylate (BADMA), bisphenol A ethoxylate diacrylate (BAEDA, EO/phenol=2 or 4) and pentaerythritol diacrylate monostearate (PDAM), were used to synthesize monolithic capillary columns for reversed phase liquid chromatography (RPLC) of small molecules. Tetrahydrofuran (THF) and decanol were chosen as good and poor porogenic solvents for BAEDA-2 and BAEDA-4 monoliths. For the formation of the BADMA monolith, THF was replaced with dimethylformamide (DMF) to improve the column reproducibility. Appropriate combinations of THF, isopropyl alcohol and an additional triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) or PPO-PEO-PPO porogen were found to be effective in forming rigid PDAM monoliths with the desired porosities. Selection of porogens for the BADMA and PDAM monoliths was investigated in further detail to provide more insight into porogen selection. Isocratic elution of alkyl benzenes at a flow rate of 0.3 μL/min was conducted for BADMA and PDAM monoliths. The peaks showed little tailing on both monoliths without addition of acid to the mobile phase. The column efficiency measured for pentylbenzene using the BADMA monolithic column was 60,208 plates/m (k=7.9). Gradient elution of alkyl benzenes and alkyl parabens was achieved with high resolution. Optimized monoliths synthesized from all four crosslinking monomers showed high permeability, and demonstrated little swelling or shrinking in different polarity solvents. Column preparation was highly reproducible; relative standard deviation (RSD) values were less than 1.2% and 7.5% based on retention times and peak areas, respectively, of alkyl benzenes.     

聚合物整体固定相的制备及条件优化

采用无搅动原位聚合模式,在聚醚醚酮柱管中直接制备了聚合物整体固定相。通过扫描电镜观察到该整体固定相的孔径分布呈双峰模式,且孔结构均匀。用压汞法测定了该固定相的孔径分布、孔隙率及比表面积等参数,考察了致孔剂组成、聚合温度及交联剂含量等参数对固定相孔结构的影响,并对制备条件进行了优化。测定了流速与柱前压的关系,实验表明此整体固定相具有良好的通透性。通过对山羊血清和低聚核苷酸的分离分析,证明了所制备的整体固定相适合用于生物大分子的分离纯化。     

Performance evaluation of long monolithic silica capillary columns in gradient liquid chromatography using peptide mixtures

A systematic study is reported on the performance of long monolithic capillary columns in gradient mode. Using a commercial nano-LC system, reversed-phase peptide separations obtained through UV-detection were conducted. The chromatographic performance, in terms of conditional peak capacity and peak productivity, was investigated for different gradient times (varying between 90 and 1320min) and different column lengths (0.25, 1, 2 and 4m) all originating from a single 4m long column. Peak capacities reaching values up to n=10(3) were measured in case of the 4m long column demonstrating the high potential of these long monoliths for the analysis of complex biological mixtures, amongst others. In addition, it was found that the different column fragments displayed similar flow resistance as well as consistent chromatographic performance in accordance with chromatographic theory indicating that the chromatographic bed of the original 4m long column possessed a structural homogeneity over its entire length.     

Rapid determination of sterols in vegetable oils by CEC using methacrylate ester‐based monolithic columns

A method for the determination of sterols in vegetable oils by CEC with UV–Vis detection, using methacrylate ester‐based monolithic columns, has been developed. To prepare the columns, polymerization mixtures containing monomers of different hydrophobicities were tried. The influence of composition of polymerization mixture was optimized in terms of porogenic solvent, monomers/porogens and monomer/crosslinker ratios. The composition of the mobile phase was also studied. The optimum monolith was obtained with lauryl methacrylate monomer at 60:40% (wt:wt) lauryl methacrylate/ethylene dimethacrylate ratio and 60 wt% porogens with 20 wt% of 1,4‐butanediol (12 wt% 1,4‐butanediol in the polymerization mixture). Excellent resolution between sterols was achieved in less than 7 min with an 85:10:5 v/v/v ACN–2‐propanol–water buffer containing 5 mM Tris at pH 8.0. The limits of detection were lower than 0.04 mM, and inter‐day and column‐to‐column reproducibilities at 0.75 mM were better than 6.2%. The method was applied to the determination of sterols in vegetable oils with different botanical origins and to detect olive oil adulteration with sunflower and soybean oils.     

整体柱在线固相微萃取-高效液相色谱同步富集检测水中的苯氧羧酸类除草剂

采用C18毛细管整体柱作为固相微萃取整体柱,构建在线固相微萃取-高效液相色谱联用系统,同步富集检测环境水样中的5种苯氧羧酸类除草剂。详细考察了联用系统运行条件对富集检测的影响。联用系统运行最佳参数为:固相微萃取整体柱长度20 cm,进样流速0.04 mL/min,进样13 min,洗脱流速0.02 mL/min,洗脱5 min。在最佳条件下,5种苯氧羧酸类除草剂的检出限为:9 μg/L (苯氧丙酸)、4 μg/L (2-(2-氯)-苯氧丙酸)、4 μg/L (2-(3-氯)-苯氧丙酸)、5 μg/L (2,4-二氯苯氧乙酸)、5 μg/L (2-(2,4-二氯苯氧基)丙酸)。与HPLC系统直接进样对比,联用系统对5种检测对象表现出优良的富集能力。5种苯氧羧酸类除草剂的回收率在79.0%~98.0%之间(RSD≤3.9%)。该方法成功应用于水样中5种苯氧羧酸类除草剂的检测,结果令人满意。