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。     

Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography

A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in comparison to the organic polymer monolith.     

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.     

Short communication performance of octadecylsilylated monolithic silica capillary columns of 530 microm inner diameter in HPLC

Monolithic silica capillary columns were successfully prepared in a fused silica capillary of 530 microm inner diameter and evaluated in HPLC after octadecylsilylation (ODS). Their efficiency and permeability were compared with those of columns pakked with 5-microm and 3-microm ODS-silica particles. The monolithic silica columns having different domain sizes (combined size of through-pore and skeleton) showed 2.5-4.0-times higher permeability (K= 5.2-8.4 x 10(-14) m2) than capillary columns packed with 3-mm particles, while giving similar column efficiency. The monolithic silica capillary columns gave a plate height of about 11-13 microm, or 11 200-13 400 theoretical plates/150 mm column length, in 80% methanol at a linear mobile phase velocity of 1.0 mm/s. The monolithic column having a smaller domain size showed higher column efficiency and higher pressure drop, although the monolithic column with a larger domain size showed better overall column performance, or smaller separation impedance (E value). The larger-diameter (530 microm id) monolithic silica capillary column afforded a good peak shape in gradient elution of proteins at a flow rate of up to 100 microL/min and an injection volume of up to 10 microL.     

Electroosmotic pump‐supported molecularly imprinted monolithic column for capillary chromatographic separation of nitrophenol isomers

In this work, a novel molecularly imprinted polymer (MIP) monolithic column with integrated in‐column electroosmotic pump (EOP) was designed and successfully prepared to facilitate the capillary chromatography with MIP column. A silica‐based EOP was synthesized at the detection end of the MIP monolithic capillary column by so‐gel to provide the hydrodynamic driven force for the capillary chromatography. Because of large surface area and low fluidic resistance of the silica monolith,a strong and steady EOF was generated by silica‐based EOP, indicating that the EOP was quite compatible with MIP capillary column. With the sufficient EOF provided by EOP, the electro‐driven based capillary chromatographic separation of nitrophenol isomers was achieved in 4‐vinylpyridine‐based MIP monolithic capillary, which was originally proved infeasible because of the EOF shortage. No significant influence upon the specific recognition of the MIP was found due to the setting of EOP after the detection window of the column. The influence of experimental parameters on the EOF such as voltage and pH value of running buffer was investigated. The column was also evaluated by capillary liquid chromatographic mode to compare with EOP‐driven capillary chromatography. Higher column efficiency was obtained by EOP‐driven separation with improved peak shape. The results suggested that EOP‐supported technique would be a good way to solve the problem of weak EOF generation in electro‐driven capillary chromatography.     

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×75μm)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。     

Chiral Monolithic Silica-Based HPLC Columns for Enantiomeric Separation and Determination: Functionalization of Chiral Selector and Recognition of Selector-Selectand Interaction

This review draws attention to the use of chiral monolithic silica HPLC columns for the enantiomeric separation and determination of chiral compounds. Properties and advantages of monolithic silica HPLC columns are also highlighted in comparison to conventional particle-packed, fused-core, and sub-2-µm HPLC columns. Nano-LC capillary monolithic silica columns as well as polymeric-based and hybrid-based monolithic columns are also demonstrated to show good enantioresolution abilities. Methods for introducing the chiral selector into the monolithic silica column in the form of mobile phase additive, by encapsulation and surface coating, or by covalent functionalization are described. The application of molecular modeling methods to elucidate the selector–selectand interaction is discussed. An application for enantiomeric impurity determination is also considered.     

The synthesis of chloropropyl-functionalized silica hybrid monolithic column with modification of N,N-dimethyl-N-dodecylamine for capillary electrochromatography separation

A chloropropyl-functionalized silica (CP-silica) hybrid monolithic column was synthesized within the confines of a capillary via the sol–gel process using tetramethoxysilane (TMOS) and (3-chloropropyl)-trimethoxysilane (CPTMS) as the precursors. The resulting CP-silica hybrid monolith inside the capillary showed homogeneous macroporous morphology and was well attached to the inner wall of the capillary. The obtained CP-silica hybrid monolithic capillary column demonstrated the inherent hydrophobic property and could be applied as a reversed-phase stationary phase in CEC directly. Due to the great chemical reactivity of the incorporated chloro groups on the hybrid silica monolithic matrix, the chloropropyl moieties on the surface of the hybrid silica monolith matrix could be conveniently further modified by a tertiary amine of N,N-dimethyl-N-dodecylamine (DMDA) via the nucleophilic substitution reaction at 70 °C to introduce a dodecyl groups (C12) onto the CP-silica hybrid monolithic matrix. The resulting C12-silica hybrid monolithic column not only demonstrated the significantly enhanced hydrophobic property in the separation of alkylbenzenes in reversed-phase capillary electrochromatography (RP-CEC), but also the strong electroosmotic flow (EOF) in a wide pH range. Five alkylbenzenes could be baseline separated in 3 min with column efficiency ranging from 189 700 to 221 000 N/m with a 70% ACN running buffer in CEC.     

Rapid determination of aliphatic amines in water samples by pressure-assisted monolithic octadecylsilica capillary electrochromatography-mass spectrometry

A pressure-assisted capillary chromatography-mass spectrometry method based on the use of a monolithic octadecylsilica (ODS) capillary is proposed for the determination of aliphatic amines. A 25 mM citric acid buffer containing 10% methanol is used as running electrolyte. Separation is achieved by simultaneously applying a capillary electrophoresis (CE) voltage of 13 kV and an overimposed pressure of 8 bar. The use of pressure is required to ensure stable electrospray conditions. Analysis times are reduced by using a capillary column consisting of a 30 cm long monolithic silica capillary column bound with ODS and a fused-silica capillary column also 30 cm long. The proposed method was successfully applied to the determination of low-molecular-weight aliphatic amines in tap and river water. The analysis of real samples requires cleanup and preconcentration, which can be performed automatically by inserting a minicolumn in the replenishment system of the commercial instrument.     

Preparation of a zeolite imidazole skeleton–silica hybrid monolithic column for amino acid analysis via capillary electrochromatography

We developed a novel, convenient and low-cost one-pot strategy for preparing a zeolitic imidazolate framework-8 (ZIF-8)–silica hybrid monolithic column by adding ZIF-8 directly to a polymer solution of the silica matrix. The simulated stationary phase and monolithic column prepared under optimal conditions were characterized using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis nitrogen physisorption and zeta potential. The results obtained confirmed the successful introduction of ZIF-8 into the silica monolithic column, and the prepared monolithic column exhibited good permeability and physicochemical stability. A capillary electrochromatography method was developed based on a ZIF-8–silica hybrid monolithic column through which 15 mixed amino acids, 4 neutral compounds, 4 nipagin esters and 2 chlorinated fungicides were separated in 14, 5, 7 and 6 min, respectively, under optimal conditions. The relative standard deviations retention times and column efficiencies in run-to-run, day-to-day and column-to-column varied in the ranges of 1.90%–2.21%, 2.13%–2.51% and 3.08%–6.65%, respectively, which demonstrated that ZIF-8–silica hybrid monolithic column exhibited satisfactory reproducibility and stability. The incorporation of ZIF-8 into a silica monolithic column is a promising method for preparing novel monolithic columns composed of a metal–organic framework.     

Highly efficient monolithic silica capillary columns modified with poly(acrylic acid) for hydrophilic interaction chromatography

Monolithic silica capillary columns for hydrophilic interaction liquid chromatography (HILIC) were prepared by on-column polymerization of acrylic acid on monolithic silica in a fused silica capillary modified with anchor groups. The products maintained the high permeability (K=5 x 10(-14)m(2)) and provided a plate height (H) of less than 10 microm at optimum linear velocity (u) and H below 20 microm at u=6mm/s for polar solutes including nucleosides and carbohydrates. The HILIC mode monolithic silica capillary column was able to produce 10000 theoretical plates (N) with column dead time (t(0)) of 20s at a pressure drop of 20 MPa or lower. The total performance was much higher than conventional particle-packed HILIC columns currently available. The gradient separations of peptides by a capillary LC-electrospray mass spectrometry system resulted in very different retention selectivity between reversed-phase mode separations and the HILIC mode separations with a peak capacity of ca. 100 in a 10 min gradient time in either mode. The high performance observed with the monolithic silica capillary column modified with poly(acrylic acid) suggests that the HILIC mode can be an alternative to the reversed-phase mode for a wide range of compounds, especially for those of high polarity in isocratic as well as gradient elution.     

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.     

Capillary monolithic titania column for miniaturized liquid chromatography and extraction of organo-phosphorous compounds

A new sol?Cgel protocol was designed and optimized to produce titanium-dioxide-based columns within confined geometries such as monolithic capillary columns and porous-layer open-tubular columns. A surface pre-treatment of the capillary enabled an efficient anchorage of the monolith to the silica capillary wall during the synthesis. The monolith was further synthesized from a solution containing titanium n-propoxide, hydrochloric acid, N-methylformamide, water, and poly(ethylene oxide) as pore template. The chromatographic application of capillary titania-based columns was demonstrated with the separation of a set of phosphorylated nucleotides as probe molecules using aqueous normal-phase liquid chromatography conditions. Capillary titania monoliths offered a compromise between the high permeability and the important loading capacity needed to potentially achieve miniaturized sample preparations. The specificity of the miniaturized titania monolithic support is illustrated with the specific enrichment of 5??-adenosine mono-phosphate. The monolithic column offered a ten times higher loading capacity of 5??-adenosine mono-phosphate compared with that of the capillary titania porous-layer open-tubular geometry.     

丙基脲硅胶毛细管整体柱的制备及性能研究

采用溶胶-凝胶技术在毛细管中原位合成硅胶整体柱,通过表面化学修饰技术制备了极性的丙基脲硅胶整体柱.对所制备的整体柱柱性能进行了评价,考察了极性物质在该整体柱上的保留行为,并对其可能的保留机理进行了探讨.研究表明,该柱在亲水作用电色谱模式下能有效分离苯酚类极性小分子化合物.     

Loading capacities of monolithic capillary columns in gas chromatography

The loading capacities of monolithic capillary columns based on silica gel and divinylbenzene are studied for two carrier gases, CO₂ and N₂. It is shown that the efficiency of the column is more sensitive to the overload of the column than the retention time of the sorbate is, especially for the CO₂ carrier gas. It is established that the loading capacity of a monolithic column based on silica gel decreases significantly in going from N₂ to CO₂. For columns based on divinylbenzene, the loading capacity is found to be virtually the same for both carrier gases. For monolithic columns, the loading capacity per one meter of column length is found to be 10 and more times higher than that for a standard open capillary column.     

Simple 2D-HPLC using a monolithic silica column for peptide separation

Separation of peptides by fast and simple two-dimensional (2D)-HPLC was studied using a monolithic silica column as a second-dimension (2nd-D) column. Every fraction from the first column, 5 cm long (2.1 mm ID) packed with polymer-based cation exchange beads, was subjected to separation in the 2nd-D using an octadecylsilylated (C18) monolithic sillica column (4.6 mm ID, 2.5 cm). A capillary-type monolithic silica C18column (0.1 mm ID, 10 cm) was also employed as a 2nd-D column with split flow/injection. Effluentof the first dimension (1st-D) was directly loaded into an injector loop of 2nd-D HPLC. UV and MS detection were successfully carried out at high linear velocity of mobile phase at 2nd-D using flow splitting for the 4.6 mm ID 2nd-D column, or with directconnection of the capillary column to the MS interface. Two-minute fractionation inthe 1st-D, 118-second loading, and 2-second injection by the 2nd-D injector, allowed one minute for gradient separation in the 2nd-D, resulting in a maximum peak capacity of about 700 within 40 min. The use of a capillary column in solvent consumption and better MS detectability compared to a larger-sized column. This kind of fast and simple 2D-HPLC utilizing monolithic silica columns will be useful for the separation of complex mixtures in a short time.     

Separation of Polar and Basic Compounds in Hydrophilic Interaction Pressurized CEC Using Diethylenetriaminopropyl Silica Monolithic Columns

A novel silica-based monolithic column possessing diethylenetriaminopropyl ligands for hydrophilic interaction pressurized capillary electrochromatography is described. The preparation of monolithic stationary phase was based on the individual silica matrix forming and subsequent chemical bonding. The triamino groups on the surface of the novel stationary phase generated a sustainable anodic electroosmotic flow under acidic conditions. A variety of neutral and basic analytes were used to evaluate the column performance. The monolithic silica stationary phase exhibited hydrophilic interaction chromatographic behavior toward neutral solutes. For basic tetracycline antibiotics, hydrophilic interaction as well as electrophoretic migration process with the monoliths was observed and peak tailing was avoided.     

One‐pot synthesis of (3‐sulfopropyl methacrylate potassium)‐silica hybrid monolith via thiol‐ene click chemistry for CEC

A novel (3‐sulfopropyl methacrylate potassium)‐silica hybrid monolithic column for CEC has been prepared by a simple one‐pot approach based on efficient thiol‐ene click chemistry. In this process, the polycondensation of hydrolyzed alkoxysilanes and in situ click reaction of vinyl groups on 3‐sulfopropyl methacrylate potassium and thiol groups on the precondensed siloxanes simultaneously occurred in a pretreated capillary. Homogeneous monolithic matrix with large through‐pores tightly bonded to the inner wall of the capillary was shown by optical microscope and SEM. The minimum plate height of this hybrid monolithic column was determined as 3.9 μm for thiourea. Anilines, alkylbenzenes, and phenols were well separated on this hybrid monolithic column by CEC, which indicated typical reversed‐phase and cation‐exchange chromatographic retention mechanisms of the column.     

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.     

Hybrid organic-inorganic octyl monolithic column for in-tube solid-phase microextraction coupled to capillary high-performance liquid chromatography

An octyl-functionalized hybrid silica monolithic column was developed for in-tube solid-phase microextraction (SPME) to perform on-line preconcentration coupled to capillary high-performance liquid chromatography (microHPLC) analysis. A hybrid silica monolithic column functionalized with octyl groups was conveniently synthesized by a two-step acid/base-catalyzed hydrolysis/co-condensation of tetraethoxysilane (TEOS) and n-octyltriethoxysilane (C8-TEOS). The size of through-pores as well as the carbon content can be adjusted by changing the ratio of TEOS to C8-TEOS in the polymerization mixture. The extraction characteristics of the monolithic column prepared under optimized fabrication conditions were studied by using polycyclic aromatic hydrocarbons (PAHs) as the analytes. The sample volume that could be injected into the system was increased up to 1mL with simultaneous increase of column efficiency, when hybrid silica monolithic column was used as a precolumn. Good linear calibration curves (R>0.999) were obtained, and the limits of detection (signal-to-noise ratio, S/N=3) for the analytes were found to be between 2.4 and 8.1ng/mL with a UV absorbance detector, which are 299-456 times lower than those obtained without preconcentration. The column-to-column RSD values were 1.3-8.0% for recoveries of PAHs investigated.