Polydimethylsiloxane-functionalized monolithic silica column for reversed-phase capillary liquid chromatography

A polydimethylsiloxane (PDMS)-modified monolithic silica column was prepared for performing reversed-phase capillary liquid chromatography. The prepared PDMS column has a permeability of 6.4×10(-14) m(2) with a plate height <9.2 μm. Alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) were well separated with the PDMS stationary phase, which exhibited similar selectivity and separation mechanism to that of octadecyl stationary phase. The hydrophobic interactions between the analytes and the PDMS stationary phase mainly play the roles for the separation of alkylbenzenes and PAHs. The characteristics of the PDMS column for the separation of alkylbenzenes and PAHs demonstrated that it would be a promising alternative to the octadecyl column.     

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.     

Electrically assisted capillary liquid chromatography using a silica monolithic column

A silica monolithic capillary column was linked to an open capillary of the same internal diameter via a Teflon sleeve to form a duplex column to investigate the combination of chromatography and electrophoresis in the mode of electrically assisted capillary liquid chromatography (eCLC). Using a commercial CE instrument with an 8.5 cm long, 100 μm i.d. reversed phase silica monolithic section and a window 1.5 cm beyond the end of this in a 21.5 cm open section, a minimum plate height of 9 μm was obtained in capillary liquid chromatography (CLC) mode at a low driving pressure of 50 psi. In eCLC mode, high speed and high resolution separations of acidic and basic compounds were achieved with selectivity tuning based on the flexible combination of pressure (0–100 psi) and voltage. Taking advantage of the excellent permeability of silica monolithic columns, use of a step flow gradient enabled elution of compounds with different charge state.     

反相硅胶整体柱离子色谱法快速分析BrO-3

研究了基于反相硅胶整体柱的离子色谱快速分析BrO;的方法.以氢氧化四丁铵(TBA)为流动相动态修饰反相硅胶整体柱,采用直接电导检测,在普通高效液相色谱仪上实现了BrO3-和常见阴离子的快速分析.实验考察并讨论了流动相、色谱柱温度和流速对所测阴离子保留和分离的影响.确定分离测定BrO3-的最佳色谱条件是:以0.75 mm...     

Separation of gold nanoparticles with a monolithic silica capillary column in liquid chromatography

A separation system for gold nanoparticles was developed using monolithic silica capillary columns with 50 μm i.d., which were prepared via in-situ sol-gel processes. Gold nanoparticles with five different average sizes were synthesized via reduction of tetrachloroauric acid (HAuCl(4)) under different synthesis conditions, and were evaluated by UV-visible spectrophotometry, dynamic light scattering as well as transmission electron microscopy before they were separated using the developed system. The results showed that all of the gold nanoparticles had a certain size distribution, and the mean sizes obtained were 13, 17, 33, 43 and 61 nm, with σ = 2.5, 2.7, 5.2, 5.1 and 5.6 nm, respectively. Transmission electron microscopy showed that the samples with mean sizes of 13 and 17 nm were almost spherical, while larger samples were slightly non-uniform. The agglomeration of gold nanoparticles as the sample could be prevented by using a sodium dodecyl sulfate aqueous solution as the mobile phase, and gold nanoparticles were retained by adsorption on the silica surface. Separation with 8 mM sodium dodecyl sulfate as the eluent and a 1000-mm column was successful, and the separation of gold nanoparticles with 61 and 17 nm or 61 and 13 nm was demonstrated. The separation results obtained using a nonporous silica packed column as well as monolithic silica columns with or without mesopore growth were compared. It was found that separation using the mesopore-less monolithic column achieved better resolution. Through the use of a 2000-mm separation column, the mixtures of 61, 43, 17 nm and 61, 33, 13 nm could be separated.     

Fast determination of tetrafluoroborate by high-performance liquid chromatography using a monolithic column

Fast determination of tetrafluoroborate by high-performance liquid chromatography using a silica-based monolithic column and direct conductivity detection was carried out. Chromatographic separation was performed on a Chromolith Speed ROD RP-18e column (50 mm x 4.6 mm i.d.) with tetrabutylammonium hydroxide (TBA-OH)+ phthalic acid as eluent. The effects of eluent concentration, eluent pH, column temperature and flow rate on retention time of tetrafluoroborate were investigated. The optimized chromatographic conditions for determination of tetrafluoroborate were using 0.5mM TBA-OH + 0.31 mM phthalic acid (pH 5.5) as eluent, column temperature of 30 degrees C and flow rate of 6.0 mL/min. Retention time of tetrafluoroborate was less than 1min under the conditions. Common anions (Cl(-), Br(-), NO3(-) and SO4(2-)) did not interfere with the determination of tetrafluoroborate. Detection limit (S/N = 2) for tetrafluoroborate was 1.4 mg/L. The linear range of calibration curve between peak area and the concentration of tetrafluoroborate was from 1.4 to 100.0 mg/L. The reproducibility was 0.09% and 1.8% (n = 5) relative standard deviation (RSD) for retention time and peak area, respectively. The method has been applied to the determination of tetrafluoroborate in ionic liquids. Recoveries of tetrafluoroborate after spiking were 98.2-101.5%.     

Reversed-phase liquid chromatography on a microchip with sample injector and monolithic silica column

In micro total analysis systems, liquid chromatography (LC) works under pressure-driven flow is the essential analysis component. There were not, however, much works on microchip LC. Here we developed a microchip for reversed-phase LC using porous monolithic silica. The chip consisted of a double T-shaped injector and a approximately 40-cm serpentine separation channel. The octadecyl-modified monolithic silica was prepared in the specified part of the channel on the microchip using sol-gel process. Furthermore, the effect of geometry of turn sections on band dispersion at turns was examined under pressure-driven flow. High separation efficiencies of 15,000-18,000 plates/m for catechins were obtained using the LC chip.     

Preparation and characterization of lauryl methacrylate-based monolithic microbore column for reversed-phase liquid chromatography

Poly(lauryl methacrylate-co-ethylene dimethacrylate) monoliths were in situ synthesized within the confines of a silicosteel tubing of 1.02 mm i.d. and 1/16" o.d. for microbore reversed-phase HPLC. In order to obtain practically useful monoliths with adequate column efficiency, low flow resistance, and good mechanical strength, some parameters such as total monomer concentration (%T), cross-linking degree (%C) and polymerization temperature were optimized. High-efficiency monoliths were successfully obtained by thermal polymerization of a monomer mixture (40%T, 10%C) with a binary porogenic solvent consisting of 1-propanol and 1,4-butandiol (7:4, v/v) at a high temperature of 90 °C. The morphology and porous structure of the resulting monoliths were assessed by scanning electron microscope (SEM) and inverse size exclusion chromatography (ISEC), while the column performance was evaluated through the separations of a series of alkylbenzenes in acetonitrile-water (50:50, v/v) eluent. At a normal flow rate of 50 μL/min (corresponding to 1.66 mm/s), the optimized monolithic columns typically exhibited theoretical plate numbers of 6000 plates/10 cm-long column for amylbenzene (k>40), and the pressure drop was always less than 1 MPa/10 cm. The monoliths, which were chemically anchored to the tube inner wall surface using a bifunctional silylation agent, exhibited adequate mechanical strength of up to 12-13 MPa, and were properly operated at 10 times higher flow rate than normal, reducing the separation time to one tenth. The lauryl methacrylate-based monolithic column was applied to a rapid and efficient separation of ten common proteins such as aprotinin, ribonuclease A, insulin, cytochrome c, trypsin, transferrin, conalbumin, myoglobin, β-amylase, and ovalbumin in the precipitation-redissolution mode. Using a linear CH(3)CN gradient elution at a flow rate of 500 μL/min (10-times higher flow rate), 10 proteins were baseline separated within 2 min.     

Analysis of wine phenolics by high-performance liquid chromatography using a monolithic type column

A polyacrylamide gel crosslinked with allyl-β-cyclodextrin can be used repeatedly for several weeks for the separation of DNA fragments, since bubbles are not generated during a run. Allyl-β-cyclodextrin can easily be synthesized in one step from allylglycidylether and β-cyclodextrin. The plate numbers for DNA fragments, up to about 1500 bp, are high: for the separation of pBR322/HaeIII fragments they were in the range 450 000–1 600 000 m⁻¹. The resolution was almost independent of the concentration of the crosslinker (allyl-β-cyclodextrin) — in sharp contrast to gels crosslinked with N,N′-methylenebisacrylamide.     

High-performance liquid chromatography with contactless conductivity detection for the determination of peptides and proteins using a monolithic capillary column

Gradient programs were applied to the determination of peptides and proteins in HPLC with contactless conductivity detection. A monolithic capillary column was used for the fast and sensitive determination of the biochemical species in acidic mobile phases consisting of acetic acid or trifluoroacetic acid in various concentrations of acetonitrile in water. The drift in baseline, which is caused by conductivity changes during the elution program, was minimized by careful optimization of the composition of the mobile phase and remaining drift was removed by computational baseline normalization. The flow rate from a conventional HPLC pump was reduced to a flow rate suitable for capillary systems using a pre-column flow splitter and a final total flow rate of 1.65 microl/min was used for all capillary HPLC separations. The contactless conductivity detector was positioned directly on the outlet capillary of the separation column and positively charged peptides and proteins were determined as sharp and symmetrical peaks. Detection limits in a concentration range from 3.7 x 10(-8) to 5.1 x 10(-7)M and a reproducibility of peak areas and peak heights between 2.3% and 7.3% were achieved for all biochemical species tested.     

Preparation of chitosan functionalized monolithic silica column for hydrophilic interaction liquid chromatography

A novel cationic hydrophilic interaction monolithic stationary phase based on the chemical modification of carboxymethyl chitosan (CMCH) to the monolithic silica skeleton using carbodiimide as an activation reagent was prepared for performing capillary liquid chromatography. The amino and hydroxy moieties of CMCH functioned as both the ion-exchange sites and polar providers. The performance of the column was studied by the separation of polar acidic compounds. The chitosan functionalized monolithic silica column showed good selectivity for nucleosides, nucleotides, aromatic acids and aliphatic acids. The mechanism for the separation of these compounds was also studied. The results showed that these compounds were separated primarily based on the hydrophilic interaction mechanism.     

硅胶整体柱离子对色谱快速分析碘离子

建立了用硅胶整体柱和直接电导检测的离子对色谱快速分析碘离子的方法。采用Chromolith Speed ROD RP-18e色谱柱,以氢氧化四丁铵(离子对试剂)-邻苯二甲酸+乙腈(有机改进剂)为淋洗液,讨论了离子对试剂浓度、有机改进剂浓度、pH、流速和色谱柱温度对碘离子保留的影响。确定最佳色谱条件为:0.25 mmol/L氢氧化四丁铵-0.18 mmol/L邻苯二甲酸+体积分数7%乙腈(pH5.5)作为淋洗液,流速6.0 mL/min,色谱柱温30℃。在此条件下,碘离子的保留时间在0.5 min之内,其它常见阴离子(Cl-、NO3-、SO42-)及SCN-、ClO4-不干扰测定。方法的检出限为0.86 mg/L,标准曲线的线性范围为1.6～85.0 mg/L,峰面积的相对标准偏差为2.3%。将方法应用于测定地下水和果汁中的碘离子,加标回收率为98.5%～104.2%。     

Determination of ricin by nano liquid chromatography/mass spectrometry after extraction using lactose-immobilized monolithic silica spin column

Ricin is a glycosylated proteinous toxin that is registered as toxic substance by Chemical Weapons convention. Current detection methods can result in false negatives and/or positives, and their criteria are not based on the identification of the protein amino acid sequences. In this study, lactose-immobilized monolithic silica extraction followed by tryptic digestion and liquid chromatography/mass spectrometry (LC/MS) was developed as a method for rapid and accurate determination of ricin. Lactose, which was immobilized on monolithic silica, was used as a capture ligand for ricin extraction from the sample solution, and the silica was supported in a disk-packed spin column. Recovery of ricin was more than 40%. After extraction, the extract was digested with trypsin and analyzed by LC/MS. The accurate masses of molecular ions and MS/MS spectra of the separated peptide peaks were measured by Fourier transform-MS and linear iontrap-MS, respectively. Six peptides, which were derived from the ricin A-(m/z 537.8, 448.8 and 586.8) and B-chains (m/z 701.3, 647.8 and 616.8), were chosen as marker peptides for the identification of ricin. Among these marker peptides, two peptides were ricin-specific. This method was applied to the determination of ricin from crude samples. The monolithic silica extraction removed most contaminant peaks from the total ion chromatogram of the sample, and the six marker peptides were clearly detected by LC/MS. It takes about 5 h for detection and identification of more than 8 ng/ml of ricin through the whole handling, and this procedure will be able to deal with the terrorism using chemical weapon.     

High-performance liquid chromatography of proteins using chemically-modified silica supports

Summary Highly efficient and fast exclusion-chromatographic separations of proteins are possible on chemically-modified, silica stationary phases. By optimizing the pH and the ionic strength of the aqueous eluent secondary interactions of the samples with surface groups can be excluded. Bonded propylamide groups proved to possess optimum properties for exclusion chromatography. With other functional groups adsorption effects cannot be excluded totally. The optimum pore size distribution for protein separation up to relative molecular masses of 500,000 daltnons is between 10nm and 50nm. With these silica-based phases the pore size distribution, the pore volume and the packing characteristics are independent of the eluent, therefore the same column can be used with aqueous as well with organic eluents. It is possible to correlate the elution volume (molecular size) of proteins with those of polystyrene standars. The recovery of the proteins and their biological activity has always been better than 90%. The potentialities of adsorption chromatography of proteins on chemically-bonded stationary plases with different functional groups are demonstrated.     

Determination of the purity of ampicillin by micellar electrokinetic chromatography and reversed phase liquid chromatography on a monolithic silica column

A micellar electrokinetic chromatographic (MEKC) method and a fast reversed-phase liquid chromatographic one have been developed for determining the purity of ampicillin. MEKC separation of ampicillin and its related substances was performed with the use of an untreated fused-silica capillary and 40 mM phosphate-borate buffer, pH 7.5 containing 75 mM SDS. The HPLC method employed a monolithic silica C18 column and a mobile phase composed of phosphate buffer, pH 5.2 and ACN, the flow rate being 4.0 mL/min. Both methods were successfully validated. Linearity, relative response factors, limits of quantitation, intermediate precision, and accuracy were evaluated. The methods proved to be fast, reliable, and sufficiently sensitive and, accordingly, well-suited for control of purity of ampicillin substance, injections, and capsules. A combination of both methods can be very useful in the confirmation of impurity profiles.     

Determination of the purity of phenoxymethylpenicillin by micellar electrokinetic chromatography and reversed phase liquid chromatography on a monolithic silica column

A micellar electrokinetic chromatographic and a fast reversed‐phase liquid chromatographic method have been developed for determination of the purity of phenoxymethylpenicillin. The optimized running buffer composition was 40 mM phosphate–borate–125 mM SDS–3.5% (v/v) methanol. The HPLC method employed a monolithic silica C18 column and a mobile phase composed of phosphate buffer, pH 3.5, and ACN, the flow‐rate being 3.5 mL/min. Both methods were successfully validated. Linearity, intermediate precision, limits of quantitation, accuracy, and a good correlation of the HPLC and MEKC results were demonstrated. Both methods proved to be fast and reliable and sufficiently sensitive. A combination of the two methods can be very useful in impurity profiling.     

Analysis of microcystins by capillary high performance liquid chromatography using a polymethacrylate-based monolithic column

A polymethacrylate-based monolithic column was prepared and its application to the separation of three kinds of similar microcystins (MCs) in capillary high performance liquid chromatography (capillary-HPLC) with ultraviolet detection was studied. The monolithic matrix contains both hydrophobic and cation-exchange interaction sites. Factors influencing the separation performance have been investigated. A baseline separation could be achieved by means of Tris(hydroxymethyl)aminomethane buffer of mildly alkaline pH and acetonitrile as the mobile phases in less than 5 min. The calibration curves were linear with a correlation coefficient r>0.9990 over a range of 0.25-18.00 mg/L. This method was successfully applied to the separation of microcystins from other compounds in spiked uncontaminated lake water after performing solid-phase extraction. The whole procedure provided low LODs, e. g. the LODs for MC-LR, MC-YR, and MC-RR were found to be 0.49, 0.67, 0.30 microg/L, respectively. The LODs, precision, efficiency, and the results obtained for the real samples demonstrate the potential of polymethacrylate-based monolithic columns as fast separation tools for routine use in the monitoring of microcystins in real water samples.     

Comparison of conventional microparticulate and a monolithic reversed-phase column for high-efficiency fast liquid chromatography of basic compounds

The effect of mobile phase flow on column efficiency for a neutral compound together with weak and strong bases was compared for conventional microparticulate (3/3.5 microm and 5 microm) silica RP columns and a monolithic silica RP. For benzene, the minimum plate height (Hmin) at optimum flow-rate (mu(opt)) for weak bases was similar for the 5 microm and the monolith phases. However, the monolith generated much flatter Van Deemter curves, such that at high flow-rate (5 ml min(-1)) the plate height was nearly 3.5 times lower on the monolith. For weak bases analysed in unbuffered mobile phases, and stronger bases with acid phosphate buffer, increased tailing was obtained on the monolith compared with the conventional phases. Nevertheless, Van Deemter plots on the monolith still showed some advantages over particulate phases, even when asymmetry factor was included in the calculation of the plate height. However, at pH 7 considerable tailing of strong bases was found using the monolith; it is not clear whether this results from unique features of the monolith structure, or whether it is due merely to usual problems of silica activity. Van Deemter plots for conventional phases may be improved considerably by operating the column at elevated temperatures. At pH 3, these improvements are influenced to a considerable extent by increases in Dm, as shown by measurements of Dm using the Taylor-Aris procedure. However, at pH 7.0, improvements are much too substantial to be explainable wholly on this basis.     

High-performance liquid chromatographic determination of amitriptyline and its main metabolites using a silica column with reversed-phase eluent. Application in mice.

A method was developed for the assay of amitriptyline, amitriptyline N-oxide, nortriptyline, desmethylnortriptyline and E (trans) and Z (cis) isomers of 10-hydroxyamitriptyline and of 10-hydroxynortriptyline in plasma and brain of animals, using high-performance liquid chromatography with ultraviolet detection (254 nm). Single extraction was performed at pH 10.5 from 0.25 ml of plasma or 1 ml of brain mixture. Chromatographic separations were achieved with a silica column and an aqueous methanol mobile phase containing ammonia. This procedure offers high sensitivity (8-10 ng/ml), high linearity (r > 0.99) and acceptable precision (coefficient of variation < or = 13.3%). The method was used to determine levels of amitriptyline and its major metabolites in mice 30 min after a single intraperitoneal administration of amitriptyline (20 mg/kg).     

Hydrothermal preparation of hybrid carbon/silica monolithic capillary column for liquid chromatography

A simple, easy and economical approach for the preparation of a hybrid carbon/silica monolithic capillary column was described for the first time by using silica monolith as framework in combination with hydrothermal carbonization at 180°C. During the preparation process, formamide was introduced to the reaction solutions to reduce the dissolution rate of monolithic silica skeleton and its optimal concentration was 1.5 M. Fourier transform infrared spectrometry, scanning electron microscopy, energy dispersive X‐ray spectrometry, and inverse size exclusion chromatography were carried out to characterize the as‐prepared column. The results demonstrated that carbon spheres ranging from 150 to 1000 nm were successfully attached to the surface of silica skeleton. The prepared hybrid carbon/silica column had a permeability of 4.4 × 10^?14 m². Chromatographic performance of the column was evaluated by separation of various compounds including alkylbenzenes, nucleosides and bases, and aromatic acids. The column exhibited an efficiency of 75 000 plates/m for butylbenzene at the optimal linear velocity of 0.23 mm/s. The successful separation of these compounds and the study on mechanism indicated that the column can be applied in mixed‐mode chromatography.