Butyl methacrylate based monoliths with different cross‐linking agents using DMF‐aqueous buffer as porogen

A simple porogen containing only DMF and aqueous buffer was used for synthesis of monolithic stationary media for CEC). Butyl methacrylate (BMA)‐based capillary monoliths were obtained using proposed porogen together with acrylic/methacrylic cross‐linking agents with different alkyl chain lengths. For this purpose, ethylene glycol dimethacrylate, butanediol dimethacrylate and hexanediol diacrylate (HDDA) were used. The monoliths with better electrochromatographic separation performance were obtained when the acrylic cross‐linking agent with the longest alkyl chain length (i.e. HDDA) was used with the proposed porogen. The electrochromatographic separation of alkylbenzenes, phenols and benzoic acids were sucessfully performed in CEC particularly using poly(BMA‐co‐HDDA) monolithic stationary phase with the column efficiency up to 270 000 plates/m.     

Preparation of Monolithic Capillary Chromatographic Columns Using Supercritical Fluid as a Porogen Solvent

Monolithic polymeric beds were synthesized in fused silica capillaries using either trimethylolpropane trimethacrylate (TRIM) or a mixture of butyl methacrylate (BMA) with ethylene glycol dimethacrylate (EDMA) as monomers. Carbon dioxide at temperature and pressure conditions above its critical values was used as a porogen solvent. The purpose of using the supercritical carbon dioxide was to have the possibility of changing the solvation power (and thus the porosity of the resulting monolith) of the porogen by pressure and temperature changes instead of changing the porogen composition. The experiments were performed using a special setup consisting of a stainless steel high-pressure reactor to which the fused silica capillary was connected. The synthesized monoliths underwent liquid chromatographic evaluation. The polyTRIM capillary monoliths were characterized by different permeability, which depended on the pressure of the synthesis. BMA/EDMA columns were applied for separation of alkylbenzenes and a model mixture of proteins.     

Neutral polar methacrylate‐based monoliths for normal phase nano‐LC and CEC of polar species including N‐glycans

Neutral diol methacrylate‐based monoliths were developed for normal phase chromatography (NPC) and NP‐CEC of polar compounds including N‐glycans. Four different diol methacrylate‐based monoliths were synthesized via the copolymerization of a functional monomer using either glyceryl monomethacrylate (GMM) or glycidyl methacrylate (GMA) and a crosslinker either ethylene dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM). While the GMM‐based monoliths yield in one reaction step polar diol methacrylate monoliths that are ready for use in NPC or NP‐CEC, the GMA‐based monoliths required a postmodification with hot sulfuric acid to convert the epoxy functions into diols before use in NPC or NP‐CEC. All the four monoliths are neutral and void of fixed charges on their surfaces but yet exhibited relatively strong EOF in NP‐CEC. The EOF is attributed to the adsorption of ions from the mobile phase thus forming the electric double layer necessary for producing a bulk mobile phase flow. Under the same in situ copolymerization conditions of GMM or GMA with either EDMA or TRIM, the GMM–EDMA monolith was the best choice in terms of retention, separation efficiency, EOF velocity in CEC and linear flow velocity in Nano‐LC.     

Dual‐templates molecularly imprinted monolithic columns for the evaluation of serotonin and histamine in CEC

To extend the application of molecularly imprinted polymers, the dual‐templates molecularly imprinted monolithic columns were developed in a capillary format. Two templates serotonin and histamine were simultaneously imprinted using two different functional monomers such as methacrylic acid (MAA) and methylenesuccinic acid (MSA) in a mixture of ethylene glycol dimethacrylate (EDMA) as a cross‐linker and AIBN as polymerization initiator dissolved in DMF as porogen. The resulting molecular imprinted polymers (MIPs) were characterized based on their performance in the CEC separation of two imprinted templates. The optimization parameters such as pH, ACN composition, and concentration of the eluent were varied to achieve best resolution and efficiency for CEC separation of templates with each MIP column. It was found that the MIP monolith column fabricated using MSA offered better resolution and separation efficiency compared to column fabricated with MAA. This work utilized the dual‐templates imprinting approach successfully and broadens the scope of multi‐templates imprinting capabilities in capillary format in CEC application.     

胃蛋白酶亲和有机聚合物毛细管整体柱的制备及性能考察

以热引发原位聚合方法制备了聚（甲基丙烯酸缩水甘油酯（glycidyl methacrylate,GMA）-乙二醇二甲基丙烯酸酯（ethyleneglycol dimethacrylate,EDMA））毛细管整体柱,对整体柱的性能进行了表征。结果表明,柱内部结构均匀、渗透性好;整体柱能够实现苯等中性小分子化合物的分离,具有反相色谱特征,重现性和稳定性良好。利用整体柱环氧基团的活性,采用间接法,以戊二醛为连接臂制备胃蛋白酶亲和手性整体柱。在毛细管电色谱模式下进行了柱分离性能研究,并对缓冲液pH值和运行电压等分离条件进行了考察。结果表明,亲和整体柱对4种碱性手性药物（奈福泮、氨氯地平、西酞普兰、扑尔敏）有拆分效果,奈福泮、氨氯地平、西酞普兰能达到基线分离。本文为蛋白质亲和毛细管电色谱整体柱的制备和应用提供了新的思路和方法。     

Incorporation of graphene oxide nanosheets into boronate‐functionalized polymeric monolith to enhance the electrochromatographic separation of small molecules

Graphene oxide (GO) nanosheets were incorporated into an organic polymer monolith containing 3‐acrylamidophenylboronic acid (AAPBA) and pentaerythritol triacrylate (PETA) to form a novel monolithic stationary phase for CEC. The effects of the mass ratio of AAPBA/PETA, the amount of GO, and the volume of porogen on the morphology, permeability and pore properties of the prepared poly(AAPBA‐GO‐PETA) monoliths were investigated. A series of test compounds including amides, alkylbenzenes, polycyclic aromatics, phenols, and anilines were used to evaluate and compare the separation performances of the poly(AAPBA‐GO‐PETA) and the parent poly(AAPBA‐co‐PETA) monoliths. The results indicated that incorporation of GO into monolithic column exhibited much higher resolutions (>1.5) and column efficiency (62 000 ～ 110 000 plates/m for toluene, DMF, formamide, and thiourea) than the poly(AAPBA‐co‐PETA). The successful application in isocratic separation of peptides suggests the potential of the GO incorporated monolithic column in complex sample analysis. In addition, the reproducibility and stability of the prepared poly(AAPBA‐GO‐PETA) monolith was assessed. The run‐to‐run, column‐to‐column and batch‐to‐batch reproducibilities of this monolith for alkylbenzenes’ retention were satisfactory with the RSDs less than 1.8% (n = 5), 3.7% and 5.6% (n = 3), respectively, indicating the effectiveness and practicability of the proposed method.     

Open tubular layer of S‐ofloxacin imprinted polymer fabricated in silica capillary for chiral CEC separation

An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin.     

Development of new polar monolithic coatings for stir bar sorptive extraction

Polar vinyl monomers have been used for the synthesis of several polymer monoliths, to serve as novel coatings for stir bar sorptive extraction; the monovinyl monomers 2‐hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) monomethacrylate) (PEGMA) were copolymerized with (apolar) divinylbenzene (DVB) and/or pentaerythritol triacrylate (PETRA), both of which are cross‐linking agents. After the optimization of the most important synthesis parameters, which included the ratio between total monomers and porogen, the nature of the porogen, and the monomer ratios, inter alia, three mechanically stable, polar monolithic coatings for stir bar sorptive extraction were obtained that were based on poly(HEMA‐co‐DVB), poly(HEMA‐co‐PETRA), and poly(PEGMA‐co‐PETRA). Thereafter, and in order to evaluate the hydrophilicity of the resulting monoliths, they were applied as materials in the stir bar sorptive extraction of a group of emerging pollutants with a wide range of polarities. The results showed that both the poly(HEMA‐co‐DVB) and poly(PEGMA‐co‐PETRA) materials could be used to extract both polar and nonpolar compounds by stir bar sorptive extraction, in an effective manner. Taking into account the desired chemical and morphological properties, as well as the extraction efficiencies, the poly(PEGMA‐co‐PETRA) material seemed to be a particularly promising monolith for application as a novel coating in stir bar sorptive extraction.     

Enantioseparation of aromatic amino acids using CEC monolith with novel chiral selector,N‐methacryloyl‐l‐histidine methyl ester

A new type of polymethacrylate‐based monolithic column with chiral stationary phase was prepared for the enantioseparation of aromatic amino acids, namely d ,l ‐phenylalanine, d ,l ‐tyrosine, and d ,l ‐tryptophan by CEC. The monolithic column was prepared by in situ polymerization of butyl methacrylate (BMA), N‐methacryloyl‐l ‐histidine methyl ester (MAH), and ethylene dimethacrylate (EDMA) in the presence of porogens. The porogen mixture included DMF and phosphate buffer. MAH was used as a chiral selector. FTIR spectrum of the polymethacrylate‐based monolith showed that MAH was incorporated into the polymeric structure via in situ polymerization. Some experimental parameters including pH, concentration of the mobile phase, and MAH concentration with regard to the chiral CEC separation were investigated. Single enantiomers and enantiomer mixtures of the amino acids were separately injected into the monolithic column. It was observed that l ‐enantiomers of aromatic amino acids migrated before d ‐enantiomers. The reversal enantiomer migration order for tryptophan was observed upon changing of pH. Using the chiral monolithic column (100 μm id and 375 μm od), the best chiral separation was performed in 35:65% ACN/phosphate buffer (pH 8.0, 10 mM) with an applied voltage of 12 kV in CEC. SEM images showed that the chiral monolithic column has a continuous polymeric skeleton and large through‐pore structure.     

Post‐polymerization modification of a new reactive monolith for reversed phase and hydrophilic interaction capillary electrochromatography of neutral,polar, and biologically active compounds

A reactive monolith based on the polymerization of 3‐chloro‐2‐hydroxypropyl methacrylate, (HPMA‐Cl), with a crosslinking agent, ethylene glycol dimethacrylate (EDMA), was synthesized and post‐functionalized with a macromolecular ligand polyethyleneimine. Monolithic columns with controlled permeability and pore structure were prepared by free radical polymerization in the presence of a binary porogenic mixture of isopropanol and decanol. The presence of chloropropyl functionality in the pristine monolith allowed the synthesis of a post‐fuctionalized monolith carrying cationic groups that was used to control the magnitude of electroosmotic flow (EOF) in electrochromatographic separation. In the synthesis of pristine monoliths, the feed concentration of functional monomer (ie, HPMA‐Cl) was changed between 30 and 60 v/v % for obtaining cationic monoliths providing satisfactory electrochromatographic separation. The best electrochromatographic performance was obtained with the polyethyleneimine functionalized monolith prepared by using the pristine monolith obtained by 60% (v/v) monomer concentration. This monolith was used in reversed phase and hydrophilic interaction capillary electrochromatography modes for the separation of alkylbenzenes, polycyclic aromatic hydrocarbons, phenols, and nucleosides, using mobile phases with low acetonitrile (ACN) contents ranging between 20% and 35% (v/v). This ACN range was remarkably lower than the content of ACN used on the hydrophilic polymethacrylate‐based monoliths reported previously (ie, >90%). The plate heights up to 5.3 μm were obtained for the separation of nucleosides with the environmental friendly mobile phases whose ACN contents were also remarkably lower than that of similar polymethacrylate‐based monoliths.     

Polymer monolithic capillary column fabricated by using monodisperse iron oxide nanocrystal template to enhance the electrochromatographic separation of small molecules

Monodisperse iron oxide nanocrystals and organic solvents were utilized as coporogens in monolithic poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) capillary columns to afford stationary phases with enhanced electrochromatographic performance of small molecules. While the conventional monoliths using organic solvents only as a porogen exhibited poor resolution (Rs) <1.0 and low efficiency of 40 000–60 000 plates/m, addition of a small amount of nanocrystals to the polymerization mixture provided increased resolution (Rs > 3.0) and high efficiency ranged from 60 000 to 100 000 plates/m at the same linear velocity of 0.856 mm/s. It was considered that the mesopores introduced by the nanocrystals played an important role in the improvement of the monolith performance. This new strategy expanded the application range of the hydrophobic monoliths in the separation of polar alkaloids and narcotics. The successful applications demonstrated that the glycidyl methacrylate based monoliths prepared by using nanocrystal template are a good alternative for enhanced separation efficiency of small molecules.     

Structural Differences Between Copolymers of Acryl‐ and Methacryl‐dicyclohexylurea with Ethylene Glycol Dimethacrylate and their Thermal Degradation Products

The present paper describes structural characteristics of crosslinked copolymers of acryl‐dicyclohexylurea (A‐DCU) and methacryl‐dicyclohexylurea (MA‐DCU) with ethylene glycole dimethacrylate (EDMA). Both copolymers decompose when heated at temperatures between 180–250°C under the separation cyclohexylisocyanate (C₆H₁₁NCO) yielding nanoporous copolymers of poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA). The comparison was also made between structural characteristics of crosslinked nanoporous copolymers of poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA) and nonporous crosslinked model compounds poly(A‐CHA‐co‐EDMA) and poly(MA‐CHA‐co‐EDMA).     

Effect of the nature of a porogen on the porous structure of monolithic polydivinylbenzene sorbents

In quartz capillaries, macroporous monolithic sorbents based on divinylbenzene are synthesized and their porous structure is studied via inverse size-exclusion-hydrodynamic chromatography. Either a single-component porogen (a higher alcohol) or a two-component porogen (a mixture of a higher alcohol and mesitylene) is used for the synthesis of monoliths. The removal of a solvent good for a polymer from a porogen results in an increase in the size of flow-through channels and a decrease in the free-space volume inside the monolith; this space is used for the separation of polymer sorbates (the working volume of a column). At the same time, the volume of micro- and mesopores in the monolith structure is practically independent of the content of the good solvent in the porogen. It is inferred that the good porogen plays an active role in formation of the macroporous structure of monoliths. The structure of monoliths obtained on the basis of the two-component porogen with the use of nonanol and mesitylene or toluene is optimum for the molecular-mass analysis of polymers.     

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.     

Poly(glycerin 1,3‐dimethacrylate)‐based monolith with a bicontinuous structure tailored as HPLC column by photoinitiated in situ radical polymerization via viscoelastic phase separation

In this article we described our new approach to the polymer monolith with its morphology tailored for HPLC application to small solutes such as drug candidates. We prepared polymer monoliths based on glycerin 1,3‐dimethacrylate, GDMA with a bicontinuous structure by in situ photoinitiated free radical polymerization (UV irradiation at 365 nm). Our photopolymerization was carried out with a monodispese ultra high molecular weight polystyrene solution in chlorobenzene uniquely formulated as a porogen. The poly‐GDMA monoliths in bulk, rod and capillary thus prepared showed a bicontinuous network‐like structure featured by their fine skeletal thickness nearly in sub μm size. This monolithic structure was considered as a time‐evolved morphology frozen by UV‐irradiation via viscoelastic phase separation induced by the said porogenic polystyrene solution. According to our μHPLC measurement with acetophenone as a model solute, the UV prepared poly‐GDMA capillary demonstrated a much shaper elution profile affording higher column efficiency and permeability as compared with the thermally prepared capillary of the same bore size. Our investigation showed experimentally that poly‐GDMA monoliths with a well‐defined bicontinuous structure could be prepared reproducibly by photoinitiated radical polymerization via viscoelastic phase separation using the said unique porogen. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4651–4673, 2008     

Fast preparation of photopolymerized poly(benzyl methacrylate-co-bisphenol A dimethacrylate) monoliths for capillary electrochromatography

A novel porous polymer monolith was prepared in situ in a fused-silica capillary using photoinitiated polymerization. Bisphenol A dimethacrylate (BPADMA) was selected as a crosslinker, copolymerized with benzyl methacrylate (BMA) in the presence of a binary porogenic solvent consisting of cyclohexanol and 1-decanol in ≤10 min. The resulting poly(BMA-co-BPADMA) monoliths exhibited good permeability and mechanical stability. Mixtures of alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs) or phenolic compounds were successfully separated by CEC. A similar monolith was also prepared with ethylene dimethacrylate (EDMA) as the crosslinker instead of BPADMA to compare the separation ability of the resulting monoliths. The results indicated that poly(BMA-co-BPADMA) monoliths have better selectivity for aromatic analytes and greater chromatographic stability in higher aqueous mobile phase.     

A new zwitterionic electrochromatographic stationary phase based on poly(3‐chloro‐2‐hydroxypropyl methacrylate‐co‐ethylene dimethacrylate) reactive monolith

A new reactive monolith, poly(3‐chloro‐2‐hydroxypropyl methacrylate‐co‐ethylene dimethacrylate), poly(HPMA‐Cl‐co‐EDMA) was synthesized and post‐functionalized by taurine (2‐aminoethane sulfonic acid) to obtain a zwitterionic stationary phase for capillary electrochromatography. The new stationary phase contained charged groups such as secondary amine providing anodic electroosmotic flow and sulfonic acid groups providing cathodic electroosmotic flow. Hence, the capillary electrochromatography separations with the new zwitterionic monolith were performed with either anodic or cathodic electroosmotic flow. The electrochromatographic separation of alkylbenzenes and phenols was successfully performed. The zwitterionic monolith also allowed the separation of nucleosides using only electrokinetic mode. Theoretical plate numbers up to ~10⁵ plates/m were achieved. Our study is the first report based on poly(HPMA‐Cl‐co‐EDMA) reactive monolith post‐functionalized with a zwitterionic ligand allowing to operate in both anodic and cathodic electroosmotic flow modes. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

高选择性透过二氧化硫气体分离膜的研究 （Ⅳ）不同烃基乙烯基亚砜接枝聚乙烯醇膜的透过性能

研究了不同烃基乙烯基亚砜接技聚乙烯醇（ＰＶＡ－ＲＶＳＯ，Ｒ＝Ｍｅ，Ｅｔ，ｔ－Ｂｕ，Ｐｈ）膜对纯ＳＯ２、Ｎ２的透过性能以及ＳＯ２／Ｎ２混合气体的分离性能，结果表明上述膜对ＳＯ２具有高的选择性，对不同烃基乙烯基亚砜接枝膜进行了比较。     

Preparation and Evaluation of Long Chain Alkyl Methacrylate Monoliths for Capillary Chromatography

This work describes the fabrication of long chain alkyl methacrylate monolithic materials for use as stationary phases in capillary liquid chromatography. After capillary inner wall surface activation with 3-(trimethoxysilyl)propyl methacrylate, monoliths were formed by copolymerization of either lauryl or stearyl methacrylate (LMA or SMA) with ethylene dimethacrylate (EDMA) as crosslinker, in the presence of azobisisobutyronitrile (AIBN) as initiator and a mixture of porogenic solvents including water, 1-propanol and 1,4-butanediol. The composition of the polymerization mixture was changed in terms of monomer, crosslinker and porogen ratio composition, in order to compare the influence of these parameters. The monoliths were prepared in 320 ??m i.d. and 200 mm length capillaries. The column morphology was characterized by optical microscopy and scanning electron microscopy (SEM). Total porosity and permeability of each column were calculated using uracil as unretained material by measuring the pressure drop across the columns as a function of linear velocity. The microglobule average size for each column was also determined using Hagen?CPoiseuille equation and compared with the SEM images. As expected, a decrease of the porogen to monomer ratio corresponded to smaller microglobules and a lower total porosity. The columns were then chromatographically evaluated; good results were obtained when these capillaries were used to separate mixtures of phenols, aromatics and drug compounds.