Preparation and evaluation of monodispersed,submicron, non‐porous silica particles functionalized with β‐CD derivatives for chiral‐pressurized capillary electrochromatography

Submicron, non‐porous, chiral silica stationary phase has been prepared by the immobilization of functionalized β‐CD derivatives to isocyanate‐modified silica via chemical reaction and applied to the pressurized capillary electrochromatography (pCEC) enantio‐separation of various chiral compounds. The submicron, non‐porous, cyclodextrin‐based chiral stationary phases (sub_μm‐CSP2) exhibited excellent chiral recognition of a wide range of analytes including clenbuterol hydrochloride, mexiletine hydrochloride, chlorpheniramine maleate, esmolol hydrochloride, and metoprolol tartrate. The synthesized submicron particles were regularly spherical and uniformly non‐porous with an average diameter of around 800 nm and a mean pore size of less than 2 nm. The synthesized chiral stationary phase was packed into 10 cm × 100 μm id capillary columns. The sub_μm‐CSP2 column used in the pCEC system showed better separation of the racemates and at a higher rate compared to those used in the capillary liquid chromatography mode (cLC) system. The sub_μm‐CSP2 possessed high mechanical strength, high stereoselectivity, and long lifespan, demonstrating rapid enantio‐separation and good resolution of samples. The column provided an efficiency of up to 170 000 plates/m for n‐propylbenzene.     

Evaluation of band broadening in chemiluminescence detection coupled to pressurized capillary electrochromatography with an off-column coaxial flow interface

A system of off-column coaxial flow chemiluminescence (CL) detection coupled to pressurized CEC (pCEC) was described. The interface utilized a reactor that introduced postcolumn CL reagent into the capillary effluents in a sheathing flow profile. To compare and evaluate band broadening of analytes caused by the detector, the typical CL compounds luminol and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) were separated and detected by pCEC or capillary HPLC (cHPLC) coupled to CL and UV detector, respectively. The results demonstrated that the band broadening caused by off-column detection interface was minimized due to the fast kinetic nature of the CL reaction. With the proposed pCEC-CL system, the detection limits of luminol and ABEI were 1.0x10(-8) and 8.0x10(-8) mol/L, respectively, which were approximately 100-fold more sensitive than those obtained with UV absorption. In addition, separation and detection of the ABEI-labeled L-lysine (L-Lys) and L-arginine (L-Arg) were accomplished by pCEC-CL method based on the principle of ABEI-potassium ferricyanide-alkaline medium CL reaction system. Under the optimum conditions, good results could be achieved compared with pCEC-UV.     

亲水作用毛细管整体柱的制备及其用于奶制品中三聚氰胺的加压毛细管电色谱分析

以甲基丙烯酸丁酯(BMA)和3-［N,N-二甲基-［2-(2-甲基丙-2-烯酰氧基)乙基］铵］丙烷-1-磺酸内盐(SPE)为单体,制备了新型的亲水作用毛细管整体柱,并通过三聚氰胺在此柱上的保留行为证明其具有亲水性。以加压毛细管电色谱(pCEC)技术为平台,优化了整体柱基于亲水作用分离分析奶制品中三聚氰胺的色谱条件。当流动相中乙腈与10 mmol/L磷酸盐缓冲液的体积比为80:20, pH为3.0,电压为3 kV,检测波长为215 nm时,三聚氰胺能获得很好的分离。方法学考察结果表明,合成的亲水整体柱具有良好的重现性和渗透性,建立的pCEC分析方法的检出限为0.05 mg/L。该方法简单方便,回收率较高,而且流动相中无需添加离子对试剂,适合于奶制品中三聚氰胺的定量测定。     

基于窄内径多孔层毛细管开管柱的纳流高效液相色谱用于N-衍生化氨基酸对映体的分离

窄内径多孔层毛细管开管柱（NPLOT柱）在生命科学领域,特别是单细胞分析领域具有较好的应用前景。本研究采用原位热引发聚合法来制备窄内径奎尼丁类手性固定相多孔层开管柱,在6 μ m i.d.的毛细管中制备有机聚合物多孔层,考察了不同热聚合时间（3、6和9 h）对NPLOT柱形貌的影响,热聚3 h和6 h制备的NPLOT柱形貌均一,多孔层厚度分别为103±51 nm和210±51 nm。将热聚合3 h制备的NPLOT柱用于纳流高效液相色谱分离N-衍生化氨基酸对映体,在2 min内即可实现基本分离,消耗的样品量仅为皮升级别。该研究将为单细胞分析提供研究手段。     

新型亲水整体柱的制备及其在毛细管液相色谱和加压电色谱中的应用

以N,N-二甲基-N-甲基丙烯酰胺基丙基-N,N-二甲基-N-丙烷磺酸内盐(SPP)为单体,季戊四醇三丙烯酸酯(PETA)为交联剂,偶氮二异丁腈(AIBN)为引发剂及两类不同的致孔剂(乙醇/乙二醇和甲醇/1,4-丁二醇)制备了两种新型亲水性整体柱。为了获得理想的柱效、电渗流速度和渗透性,对制备整体柱的各反应物配比进行了研究和优化。比较了两种整体柱在渗透性和分离样品方面的性能,结果表明,以乙醇/乙二醇为致孔剂制备的整体柱在柱效、分离度方面优于以甲醇/1,4-丁二醇为致孔剂制备的整体柱,但在渗透性方面不及后者。探讨了流动相中盐浓度对核苷类样品保留的影响,发现当甲酸铵浓度从10 mmol/L增加到70 mmol/L时,核苷样品的保留因子呈现先增加后减小的状态。将制备的整体柱用于毛细管液相色谱和加压电色谱分别分离胺类、酚类和核苷类样品,获得了理想的分离效果。在分离酚类和核苷类混合样品时,发现加压毛细管电色谱在分离度和分离速度上均优于毛细管液相色谱。     

Development of a new method for analysis of Sudan dyes by pressurized CEC with amperometric detection

A new analytical method, pressurized CEC (pCEC) with amperometric detection (AD) using 1.5 microm RP nonporous silica packed columns has been developed for the rapid separation and determination of four Sudan dyes in hot chilli. The influence of several experimental parameters on the retention behavior has been investigated. The electrochemical oxidation of Sudans I-IV separated by pCEC can be reliably monitored with a carbon electrode at +0.95 V (vs. Ag/AgCl). Fast and efficient separation of the analytes was achieved within 7 min by pCEC under the optimum conditions with an ACN/water (95:5%) mobile phase containing formic acid (pH 4.3), 5% acetone and 0.002% triethylamine using a separation voltage of 12 kV. The detection limits for four Sudan dyes ranged from 8.0 x 10(-7) to 1.2 x 10(-6) mol/L. To evaluate the feasibility and reliability of this method, the proposed pCEC-AD method was further demonstrated with hot chilli samples spiked with Sudan dyes.     

强阳离子交换毛细管液相色谱-反相加压毛细管电色谱二维系统的构建及其在中药黄柏提取物分离中的应用

加压毛细管电色谱(pCEC)具有电泳和液相色谱的双重分离机理,其柱效高、选择性强、分辨率高和分离速度快并可进行梯度洗脱。我们在此基础上加入离子交换色谱模式,构建了强阳离子交换-反相加压毛细管液相色谱(micro strong cation exchange liquid chromatography/reversed phase pressurized capillary electrochromatography, μ-SCXLC/RP-pCEC)二维系统,并对中药黄柏的提取物进行了优化分离。第一维μ-SCXLC采用线性盐梯度分离,样品被切割成11个馏分洗脱收集后进入第二维,第二维脱盐后,采用RP-pCEC进行分离分析,梯度洗脱。以中药黄柏提取物为样品,此二维系统的分辨率和峰容量都较一维系统有很大提高,理论峰容量可达900左右,证明构建的二维体系非常适合复杂样品的分离分析。     

High-efficiency peptide analysis on monolithic multimode capillary columns: Pressure-assisted capillary electrochromatography/capillary electrophoresis coupled to UV and electrospray ionization-mass spectrometry

High-efficiency peptide analysis using multimode pressure-assisted capillary electrochromatography/capillary electrophoresis (pCEC/pCE) monolithic polymeric columns and the separation of model peptide mixtures and protein digests by isocratic and gradient elution under an applied electric field with UV and electrospray ionization-mass spectrometry (ESI-MS) detection is demonstrated. Capillary multipurpose columns were prepared in silanized fused-silica capillaries of 50, 75, and 100 microm inner diameters by thermally induced in situ copolymerization of methacrylic monomers in the presence of n-propanol and formamide as porogens and azobisisobutyronitrile as initiator. N-Ethylbutylamine was used to modify the chromatographic surface of the monolith from neutral to cationic. Monolithic columns were termed as multipurpose or multimode columns because they showed mixed modes of separation mechanisms under different conditions. Anion-exchange separation ability in the liquid chromatography (LC) mode can be determined by the cationic chromatographic surface of the monolith. At acidic pH and high voltage across the column, the monolithic stationary phase provided conditions for predominantly capillary electrophoretic migration of peptides. At basic pH and electric field across the column, enhanced chromatographic retention of peptides on monolithic capillary column made CEC mechanisms of migration responsible for separation. The role of pressure, ionic strength, pH, and organic content of the mobile phase on chromatographic performance was investigated. High efficiencies (exceeding 300 000 plates/m) of the monolithic columns for peptide separations are shown using volatile and nonvolatile, acidic and basic buffers. Good reproducibility and robustness of isocratic and gradient elution pressure-assisted CEC/CE separations were achieved for both UV and ESI-MS detection. Manipulation of the electric field and gradient conditions allowed high-throughput analysis of complex peptide mixtures. A simple design of sheathless electrospray emitter provided effective and robust low dead volume interfacing of monolithic multimode columns with ESI-MS. Gradient elution pressure-assisted mixed-mode separation CE/CEC-ESI-MS mass fingerprinting and data-dependent pCE/pCEC-ESI-MS/MS analysis of a bovine serum albumin (BSA) tryptic digest in less than 5 min yielding high sequence coverage (73%) demonstrated the potential of the method.     

Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC×GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5kHz. The use of long, relatively narrow open tubular capillary columns and a 40°C/min programming rate were explored for 1D-GC, specifically a 40m, 180μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ～1.5s, hence a peak capacity production of 40peaks/min. In contrast, use of modified injection produced ～500ms peak widths for 1D-GC, i.e., a peak capacity production of 120peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%'s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC×GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500-800peaks/min), ～5-fold to 8-fold higher than typically reported for GC×GC.     

Pressurized capillary electrochromatographic assay of trimethoprim impurities using 1 microm particle-based columns

One micrometre silica particles, derivatized with C18, were electrokinetically packed into a 75-microm-i.d. capillary. The resulting column was evaluated for the separation of trimethoprim (TMP) and its impurities using pressurized capillary electrochromatography (pCEC), starting from a capillary liquid chromatographic (CLC) separation. These samples require gradient elution when separated by high performance liquid chromatography (HPLC), but with the new columns isocratic elution suffices for their separation by CLC or pCEC. Only 70,000 theoretical plates/m for impurity C were achieved using CLC mode at relative low pressure (78 bar) although very small particles were utilized. When a voltage above 2 kV (50 V/cm) was applied, unknown peaks appeared, which was assumed due to an electrophoretic effect with the unknown peaks resolving as a result of the applied voltage. In order to minimize these unfavorable contributions, only a low voltage was applied, still leading to higher separation performances and shorter separation times than in CLC. The optimal analyzing conditions in pCEC included a pressure of 78 bar, an applied voltage of 1 kV, and a mobile phase consisting of 80 mM sodium perchlorate (pH 3.1)/methanol (60/40, v/v). These conditions were used to separate and quantify four major impurities in TMP within 22 min. The obtained calibration curves were linear (r>0.9980) in concentration ranges between 0.005 and 0.1 mg/mL for impurities A and C; 0.02 and 0.10 mg/mL for impurity F; and 0.01 and 0.10 mg/mL for impurity H. The detection limits (S/N=3) for impurities A, C, F, and H were 0.52, 0.84, 3.18, and 2.41 microg/mL, respectively. The calibration curves were successfully applied to analyze spiked bulk samples, with mean recoveries ranging from 92% to 110%. The developed method can therefore be considered simple, rapid, and repeatable.     

Enantioseparation on cellulose dimethylphenylcarbamate-modified zirconia monolithic columns by reversed-phase capillary electrochromatography

This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol–gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM). The process of the preparation of the zirconia monolithic capillary column was investigated by varying the concentrations of the components of the sol solution including polyethylene glycol, water and acetic acid. CDMPCZM is mechanically stable and no bubble formation was detected with the applied current of up to 30 μA. The enantioseparation behavior of the CDMPCZM columns was investigated by separating a set of 10 representative chiral compounds by varying the applied voltage and pH and organic composition of the aqueous organic mobile phases.     

Molecularly imprinted polymers as tools for the screening of felodipine from dihydropyridine calcium antagonists by pressurized capillary electrochromatography

A group of structurally similar dihydropyridine calcium antagonists (DHPs) and related compounds were used to simulate a combinatorial library. A molecularly imprinted polymer (MIP) comprising felodipine (FLD) was synthesized in situ inside the capillary for use in the separation of FLD from other DHPs by pressurized electrochromatography (pCEC). To evaluate the feasibility of using the MIP columns for the separation of FLD, parameters including pH, the applied voltages, and the effect of organic modifier were studied. The results indicated that the MIP columns demonstrated better recognition properties over a pH range of 4–6. The efficiency (plates/m) at pH 5.0 for the non-imprinted analytes was 117,000 for thiourea, 18,700 for nicarpidine, 17,300 for nisoldipine, and 14,600 for nifedipine; however, the efficiency for the imprinted analyte FLD was low, as evidenced by the broad peak, yielding only 5,100 plates/m. The column efficiency was also investigated under both micro-HPLC and pCEC conditions.     

The Effects of the Column Length on the Efficiency of Capillary Zwitterionic Organic Polymer Monolithic Columns in HILIC Chromatography

Organic polymer monolithic columns of different lengths have been prepared in 320 µm i.d. fused silica capillary by in situ radical polymerization of N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine as a zwitterionic functional monomer and bisphenol A glycerolate dimethacrylate as a crosslinking monomer in the presence of porogenic solvents. The zwitterionic monolithic columns are intended for separations of polar compounds in hydrophilic interaction chromatography (HILIC). The effects of the capillary column length, from 115 to 175 mm, on separation efficiency, were investigated under HILIC conditions, using 95:5 acetonitrile in water as the mobile phase. The extra-column contributions to band broadening significantly decrease the efficiency (apparent height equivalent to a theoretical plate), especially for weakly retained samples, and increase with diminishing column length. The experimental height equivalents of theoretical plate, HETP, were corrected for the extra-column contributions, which were determined for a series of columns by extrapolation to zero column length. On a 175 mm long column, the column efficiency, HETP = 16.5 μm, measured at the optimum linear flow velocity of 0.5 mm s⁻¹, improved to HETP = 5 µm, after correction for extra-column contributions. For more strongly retained small polar compounds, interactions with zwitterionic groups and (or) water adsorbed inside the pores decrease the column efficiency at higher flow rates.

     

Use of small diameter WCOT columns for ultra-high resolution GC/MS

For clinical and environmental analyses utilizing capillary gas chromatography/mass spectrometry (GC/MS), increased sensitivity and speed of analysis are highly desirable. These performance advantages are realized using a WCOT column of 100 μm i.d. as compared to the more conventional 200 μm i.d. capillary columns. The improved sensitivity of capillary direct GC/MS with the 100 μm i.d. column for the confirmation of drugs of abuse will be demonstrated. For environmental analysis, the superior efficiency and resolution of the 100 μm i.d. column can be employed for the separation of priority pollutants. This approach is more amenable to capillary direct GC/MS providing a more effective interface to the mass spectrometer. As a result improved sensitivity and a considerable decrease in analysis time is achieved over that obtained with the larger diameter environmental specialty phase columns.     

毛细管电色谱和加压毛细管电色谱的进展与应用

毛细管电色谱(CEC)以内含色谱固定相的毛细管为分离柱,以电渗流为驱动力,既可以分离带电物质也可以分离中性物质。它结合了毛细管电泳和高效液相色谱两者的优点,兼具高柱效、高分辨率、高选择性和高峰容量的特点,同时具有色谱和电泳的双重分离机理。然而,“纯粹”的电色谱在实际应用中有着天然的弱点,即: 在电流通过毛细管柱中的流动相时容易产生气泡(焦耳热作用),从而使电流中断和电渗流停止,毛细管柱必须被重新用流动相润湿后方能再次使用。加压毛细管电色谱(pCEC)将液相色谱中的压力流引入CEC系统中,不仅解决了气泡、干柱等问题,而且实现了定量阀进样和二元梯度洗脱。CEC和pCEC作为微分离领域的两种前沿技术,满足了当前复杂样品分析和分析仪器微型化的需求,近年来获得了广泛的关注。本文综述了这两种技术近来的发展,包括仪器、色谱固定相的发展,总结了其在生命科学、药物分析、食品安全以及环保样品分析等方面的应用进展,评述了各方法的特点,并展望了CEC和pCEC今后的发展和应用前景。     

On-line coupling of pressurized capillary electrochromatography with end-column amperometric detection for analysis of estrogens

An improved technique, pressurized capillary electrochromatography (pCEC) coupling with end-column amperometric detection (AD), was developed and used for the separation and determination of estrogens. The effects of pH value, composition of mobile phase, concentration of the surfactant sodium dodecyl sulfate (SDS) and applied voltage on separation were investigated. The electrochemical oxidation of diethylstilbestrol (DES), dienestrol (DE), and hexestrol (HEX) could be reliably monitored with a carbon electrode at 0.9 V (vs. Ag/AgCl). The pCEC analyses were performed on a capillary separation column packed with 3 microm C18 particles with an acetonitrile/water (31%: 69%) mobile phase containing Tris buffer (5 mmol/L, pH 4.5) and 4 mmol/L SDS. High voltage up to 12 kV reduced the retention time dramatically and still provided a baseline resolution. In addition, supplementary pressure prevented bubble formation and provided reliability and reproducibility of the pCEC performance. The detection limits for the three estrogens ranged from 1.2 to 2.2x10(-7) mol/L, about 10 20-fold lower than those obtained with pCEC-UV detection. To evaluate the feasibility and reliability of this system, the proposed pCEC-AD method was further demonstrated with fish muscle samples spiked with estrogens.     

Silica particles encapsulated poly(styrene-divinylbenzene) monolithic stationary phases for micro-high performance liquid chromatography

In the paper we demonstrate a new approach for the preparation and application of continuous silica bed columns that involve encapsulation (entrapment) of functionalized silica microparticles, which can be used as packing material in micro high performance liquid chromatography (micro-HPLC) and capillary electrochromatography (CEC). Like traditional packed columns, these capillaries possess characterized silica particles that offer high phase ratio and narrow pore size distribution leading to high retention and separation efficiency, respectively. More importantly, immobilization of the microparticles stabilizes the separation bed and eliminates the need for retaining frits. The developed capillary columns were fabricated in exactly the same way as a packed capillary column (slurry packing) but with an additional entrapment step. This immobilization of the packed bed was achieved by in situ polymerization of styrene and divinylbenzene in presence of decanol as a porogen and azobisisobutyronitrile as thermal initiator. Silica particles with different particle sizes and pore sizes ranging from 60 to 4000 A were studied. In addition different modified silica was used, including C-18 reversed phase, anion exchange and chiral stationary phases. Efficient separation of polyphenolic compounds, peptides, proteins and even DNA mutation were achieved using the developed technique depending on the properties of the silica particles used (particles pore size). For example, using 3 microm ProntoSIL C-18 particles with 300 A pore size, separation efficiencies in the range of 120,000-200,000 plates/m were obtained for protein separation, in a 6 cm x 200 microm i.d. capillary column. Using encapsulated silica C-18 with 1000 A pore size, separation of DNA homo and hetero duplexes were achieved under denaturing HPLC conditions for mutation detection. In addition, nucleotides were separated using anion exchange material encapsulated with poly(styrene-divinylbenzene) (PS/DVB), which indicated that the chromatographic properties of the silica packing material were still active after polymerization. The prepared capillary columns were found to be stable and could easily be operated continuously up to a pressure of 350 bar without column damage and capillary can be cut to any desired length.     

Pressure‐assisted CEC versus CEC using methacrylate‐based monolithic columns: Influence of the polymerization‐mixture composition

Pressure‐assisted CEC (pCEC) can either be performed on a CE instrument by adding pressure at the column inlet, or by applying voltage on a capillary liquid chromatography system. This study investigates the pressure's added value in pCEC using an LC instrument as well as the influence of the polymerization‐mixture composition on monolithic columns in such experimental circumstances. Two factors of the polymerization mixture, which is used to prepare the monolithic capillary columns, were varied according to an experimental design approach: the pore‐forming solvent/total monomer ratio and the pore‐forming solvents composition. Initially, the effect of the resulting stationary phase on the elution behavior of mainly pharmaceutical compounds was studied. Four responses were used to evaluate the effects on the chromatography: retention time, retention factor, peak asymmetry and number of theoretical plates. After processing the results, the stationary phase composition with the best chromatographic behavior was determined and tested. The advantageous properties of this stationary phase compared with the design center‐point column were demonstrated. Secondly, the results of these pCEC experiments were compared with those generated in an identical experimental setup previously performed using CEC. Chromatographic conditions were chosen so that the center‐point column showed similar retention in CEC and pCEC. The expected advantage (faster analysis) and drawback (decreased efficiency) of pCEC in the analysis of pharmaceuticals was evaluated. Analysis time and efficiency were both found to depend greatly on the porosity of the column. The conclusion of this comparison is that pCEC did not have a significant added value to CEC. However, this was mainly due to the instrument's limitation of the pressure‐driven flow over the column. A clear benefit of the pCEC setup was apparatus‐related, i.e. the presence of a loop injection system on the pCEC instrument, which avoids the injection problems that were occasionally observed in CEC.     

Novel method to prepare polystyrene-based monolithic columns for chromatographic and electrophoretic separations by microwave irradiation

Microwave irradiation can provide a viable alternative to the traditional means such as ultraviolet light and thermal initiation for the preparation of monolithic capillary columns. Polystyrene-based monolithic stationary phases were prepared in situ in fused-silica capillaries and simultaneously in vials. The column permeability, electrophoretic and chromatographic behavior were evaluated using pressure-assisted capillary electrochromatography (pCEC), capillary electrochromatography (CEC) and low pressure liquid chromatography (LPLC). With an optimal monolithic material, the largest theoretical plates for preparing the column could be close to 18,000 plates/m for thiourea in the mode of pCEC. Furthermore, the influence of the composition of the porogenic solvents (toluene/isooctane) on the morphology of organic-based monoliths [poly(styrene-divinylbenzene-methacrylic acid)] was systematically studied with mercury intrusion porosimetry and scanning electron microscopy. The monoliths which were prepared with a high content of isooctane had a bigger pore size and better permeability, and hence resulted in a faster separation.     

PoraPLOT Q: A porous layer open tubular column coated with styrene-divinylbenzene copolymer

A porous polymer is deposited on the inner wall of fused silica capillary columns. The retention characteristics of this porous polymer were evaluated and found to be comparable with Porapak Q. The porous polymer has a high retention volume which enables the separation of permanent gases at ambient temperatures or higher. The hydrophobic character of the porous polymer allows the injection of water containing samples without changing retention due to adsorption of water. The inertness of the porous polymer allows the elution of a range of apolar and polar compounds. The maximum temperature of the porous polymer was estimated to be 250°C. With this new type of capillary column, high resolution separations are obtained in combination with short analysis times.