Biomedical subjects

Weibing Zhang

Publications and source records attributed to Weibing Zhang.

At least 37 records · Page 2Linked to original sources

PubMed2005

[Preparation and optimization of polymer-based monolithic stationary phase for high performance liquid chromatography].

Unstirred in-situ polymerization was employed to directly produce glycidyl methacrylate-ethylene dimethacrylate copolymer (poly(GMA-co-EDMA)) monoliths. Mercury intrusion method was adopted to measure some parameters of the monoliths, such as pore size distribution, porosity and specific surface area. Effects of key variables such as composition of pore-forming solvent mixture, temperature and content of cross-linking reagent, divinyl monomer on porous structure of monoliths were studied. The optimization of preparation conditions was achieved. Homogeneous micro porous structure was observed in the monoliths by scanning electron microscope. The effect of flow rate on back pressure was investigated, and good permeability of the monolithic stationary phase was obtained. The monolithic column was also used for the separation of goat serum and five oligonucleotides, and the results proved that the monolithic column is suitable for the separation of biopolymers.

Chromatography, High Pressure Liquid↗

PubMed2005

[A study on peak compression effect in ion-exchange capillary electrochromatography with relaxation theory].

Due to the electric characteristics of the solute transport in capillary electrochromatography (CEC), some special phenomena might occur. An example is the peak compression effect in ion-exchange capillary electrochromatography, which cannot be explained with common chromatography theory. According to the basic model of relaxation theory, it is considered that there are "co-" and "counter-" solute flows in mobile phase and in stationary phase, the expressions of the first moment and the second center moment of profile, and column efficiency are derived by the method of Laplace transform. The relations of electrophoresis velocity, electroosmosis velocity and electric dispersion velocity are also investigated with these expressions. The results show that this new model offers a better explanation for peak compression effect on the migration behaviour of charged solute in CEC. The retention time will be shorter by peak compression effect, which is similar to a solvent gradients process. The peak compression effect is not steady, and doesn't appear until the conditions are fitted in some special situation.

Capillary Electrochromatography↗

PubMed2005

[Advances in packing capillary electrochromatographic columns].

The columns in capillary electrochromatography can be classified into three classes: open tubular, packed and monolithic columns. The monolithic columns can be divided into three categories: organic polymer-based monolithic columns made from the polymerization of acrylamide, styrene, acrylate or methacrylate monomers, silica-based monolithic columns generally prepared by using sol-gel technology, and packed particulate-based monolithic columns. Monolithic columns are receiving quite remarkable attention and developing rapidly with a focus on monolithic stationary phases prepared from synthetic polymers. The preparation methods for various types of capillary electrochromatographic columns and their advantages and disadvantages are reviewed according to 100 research articles. In particular, recent advances in the preparation methods of monolithic columns and their applications are discussed in details.

Capillary Electrochromatography↗

PubMed2005

[Preparation and evaluation of organic-inorganic hybrid silica-based monolithic columns for capillary electrochromatography].

A new type of organic-inorganic hybrid porous silica-based monolithic columns was developed for reversed-phase capillary electrochromatography (RP-CEC). The monolithic columns were prepared from in situ co-condensation of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PTES) precursors via a two-step catalytic sol-gel procedure in the capillary to create phenyl groups distributed throughout the silica matrix for chromatographic interaction. The functionalized monolithic stationary phase was created without additional surface derivatization. The reaction conditions for the preparation of the monolithic columns were optimized. The structure and pore size distribution of the monolithic columns were characterized by scanning electron microscopy and mercury porosimetry, respectively. The effect of water concentration on the column structure was studied, and the influence of the ratio of two precursors on the pore size distribution was also investigated. The retention behavior of polycyclic aromatic hydrocarbons on the monolithic column is discussed. Seven phenols were also separated with an average efficiency over 100 000 plates/m.

Capillary Electrochromatography↗

PubMed2005

[Determination of the dissociation constants of basic compounds by reversed-phase high performance liquid chromatography on C12-zirconia].

The high performance liquid chromatographic (HPLC) behavior of aromatic amines and pyridine derivatives was studied on a new reversed-phase stationary phase, C12-alkyl-modifled zirconia. The effects of mobile phase variables such as methanol content and pH were investigated. The results showed that the stationary phase was stable in the mobile phase with a pH range of 2 - 12. It was found that on the new stationary phase the bases demonstrated the "traditional" behavior of retention due to their hydrophobicity. The retention factors of these basic compounds on the stationary phase increased rapidly with pH from pH 2 -7, and then increased slowly until reaching a constant value. The dissociation constants (pKa) of 13 basic compounds were determined based on the relationship between their retention factors and the pH of mobile phase. Compared with references, the errors of the pKa values obtained by this HPLC method were within 0.35 pH units.

Amines↗

PubMed2004

Pressurized electrochromatography coupled with electrospray ionization mass spectrometry for analysis of peptides and proteins.

Pressurized capillary electrochromatography (pCEC) was coupled with electrospray ionization mass spectrometry (ESI-MS) using a coaxial sheath liquid interface. It was used for separation and analysis of peptides and proteins. The effects of organic modifier and applied voltage on separation were investigated, and the effects of pH value of the mobile phase and the concentration of the electrolyte on ESI-MS signal were investigated. The resolution and detection sensitivity with different separation methods (pCEC, capillary high-performance liquid chromatography) coupled on-line with mass spectrometry were compared for the separation of a peptide mixture. To evaluate the feasibility and reliability of the experimental setup of the system, tryptic digests of cytochrome c and modified protein as real samples were analyzed by using pCEC-ESI-MS.

Electrochemistry↗

PubMed2004

An etched porous interface for on-line capillary electrophoresis-based two-dimensional separation system.

The construction and evaluation of an on-column etched fused-silica porous junction for on-line coupling of capillary isoelectric focusing (CIEF) with capillary zone electrophoresis (CZE) are described. Where two separation columns were integrated on a single piece of fused-silica capillary through the etched approximately 4 to 5-mm length porous junction along the capillary. The junction is easily prepared by etching a short section of the capillary wall with HF after removing the polyimide coating. The etched section becomes a porous glass membrane that allows only small ions related to the background electrolyte to pass through when high voltage is applied across the separation capillary. The primary advantages of this novel porous junction interface over previous designs (in which the interface is usually formed by fracturing the capillary followed by connecting the two capillaries with a section of microdialysis hollow fiber membrane) are no dead volume, simplicity, and ruggedness, which is particularly well suited for an on-line coupling capillary electrophoresis-based multiple dimensional separation system. The performance of the 2D CIEF-CZE system constructed by such an etched porous junction was evaluated by the analyses of protein mixtures.

Electrophoresis, Capillary↗

PubMed2004

Hybrid organic-inorganic monolithic stationary phase for acidic compounds separation by capillary electrochromatography.

A novel type of organic-inorganic hybrid porous silica-based monolithic stationary phase for capillary electrochromatography (CEC) has been developed by sol-gel chemistry combined with supramolecular template-based approach in a simple and rapid manner. Both chromatographic interaction and electrophoretic migration contribute to the separation of acidic compounds by the monolithic column. Eight organic acids were separated rapidly with column efficiency up to 267,000 theoretical plates/m. The influences of buffer concentration and organic modifier content on the separation have been investigated. In addition, the hybrid monolithic column was used to separate triterpenoids from Ganoderma lucidum.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2004

Separation of acidic and basic compounds in capillary electrochromatography with polymethacrylate-based monolithic columns.

Methacrylate-based monolithic columns with electroosmotic flow (EOF) or very weak EOF are prepared by in situ copolymerization in the presence of a porogen in fused-silica capillaries pretreated with a bifunctional reagent. Satisfactory separations of acidic and basic compounds on the column with EOF at either low or high pH are achieved, respectively. With sulfonic groups as dissociation functionalities, sufficient EOF mobility still remains as high as 1.74 x 10(-4) cm2 s(-1) V(-1) at low pH. Under this condition, seven acidic compounds are readily separated within 5.7 min. Moreover, at high pH, the peak shape of basic compounds is satisfactory without addition of any masking amines into running mobile phase since the secondary interaction between the basic compounds and the monolithic stationary phase are minimized at high pH. Reversed-phase mechanism for both acidic and basic compounds is observed under investigated separation conditions. In addition, possibilities of acidic and basic compound separations on a monolithic column with extremely low EOF are discussed.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2004

On-line concentration of neutral and charged species in capillary electrochromatography with a methacrylate-based monolithic stationary phase.

A method involving self-concentration, on-column enrichment and field-amplified sample stacking for on-line concentration in capillary electrochromatography with a polymer monolithic column is presented. Since monolithic columns eliminate the frit fabrication and the problems associated with frits, the experimental conditions could be more flexibly adjusted to obtain higher concentration factor in comparison with conventional particulate packed columns. With self-concentration effect, the detection sensitivity of benzene and hexylbenzene is improved by a factor of 4 and 8, respectively. With on-column enrichment and ultralong injection, improvement as high as 22,000 times in detection sensitivity of benzoin is achieved. Furthermore, a combination of the three above-mentioned methods yields up to a 24,000-fold improvement in detection sensitivity for caffeine, a charged compound. Parameters affecting the efficiency of on-line concentration are investigated systematically. In addition, equations describing on-line concentration process are deduced.

Benzene↗

PubMed2004

Repeatedly usable immobilized pH gradient in a monolithic capillary column.

Glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA) were used to synthesize a monolithic capillary column containing reactive epoxy groups. Glutaraldehyde was introduced and linked to the monolith after a process of amination. An aqueous solution of commercial carrier ampholytes (CAs, Ampholine) was focused in such a polymer column. The primary amino groups of CAs reacted with glutaraldehyde along the capillary. CAs were immobilized at different positions in the column according to their isoelectric points (pI), resulting in a monolithic immobilized pH gradient (M-IPG). Isoelectric focusing (IEF) was performed without CAs in such an M-IPG column. Due to the covalent attachment of the CAs this M-IPG can be repeatedly used after its preparation. Good stability, linearity, and reproducibility were obtained.

Amination↗

PubMed2004

[Micellar electrokinetic capillary chromatographic separation of amino acids derivatized with 2-(9-carbazole)-ethyl chloroformate as a pre-column labeling reagent].

2-(9-Carbazole)-ethyl chloroformate (CEOC) has been used for the pre-column derivatization of amino acids in micellar electrokinetic capillary chromatography (MEKC). Nine amino acid standards (Ser, Thr, Gly, Glu, Asp, Val, Ile, Leu, Phe) were labeled with CEOC and separated in a buffer system containing 20 mmol/L borate-30 mmol/L sodium lauryl sulfate (SDS) and 3% acetonitrile at pH 9.0 with an applied voltage of 18 kV and column temperature of 25 degrees C. The derivatives were detected at UV 214 nm. Under optimal conditions, this method offers a baseline separation for nine CEOC-derivatized amino acids within 14 min. The linearity range was from 0.025 to 0.25 mmol/L and the detection limits were from 2.15 to 2.46 micromol/L.

Amino Acids↗

PubMed2003

Two-dimensional capillary electrophoresis involving capillary isoelectric focusing and capillary zone electrophoresis.

Capillary isoelectric focusing (cIEF) and capillary zone electrophoresis (CZE) was on-line hyphenated by a dialysis interface to achieve a 2D capillary electrophoresis (CE) system. The system was used with just one high-voltage power supply and three electrodes (one cathode shared by the two dimensions). The focused zone in the first dimension (i.e. the cIEF) was driven to the dialysis interface by electroosmotic flow (EOF), besides chemical mobilization from the first anode to the shared cathode. And then in the second dimension (i.e. the CZE), the separated zone was further separated and driven by an inverted EOF, which originated from the charged layer of a cationic surfactant adsorbed onto the inner wall of the capillary. Finally, a solution of ribonuclease was rapidly separated to assess the feasibility of the two-dimensional CE implement.

Electrolytes↗

PubMed2003

Determination of 1-phenyl-3-methyl-5-pyrazolone-labeled carbohydrates by liquid chromatography and micellar electrokinetic chromatography.

In this paper, the method for the derivatization of carbohydrates with 1-phenyl-3-methyl-5-pyrazolone (PMP) was simplified. One-third of the derivatization time was saved. Five monosaccharide derivatives have been well separated by MEKC and HPLC under optimized conditions. Good reproducibility could be obtained with relative standard deviation (RSD) values of the migration times within 5.0 and 2.3%, respectively. Furthermore, the developed methods have been successfully applied to the analysis of carbohydrates in Aloe powder and food. These methods are quite useful for routine analysis of monosaccharides and oligosaccharides in real samples.

Antipyrine↗

PubMed2003

Melatonin in Chinese medicinal herbs.

Melatonin is a highly conserved molecule that not only exists in animals, but also is present in bacteria, unicellular organisms and in plants. Since melatonin is an antioxidant, in plants melatonin was speculated to protect them from intrinsic and environmental oxidative stress. More importantly, melatonin in edible plants inevitably enters animals and human through feed and food. In this study, more than 100 Chinese medicinal herbs were analyzed using the methods of solid phase extraction and HPLC-FD on-line with MS to determine whether melatonin is present in these commonly used herbs. Melatonin was detected in majority of these plants. Sixty-four of them contain melatonin in excess of 10 ng per gram dry mass. Melatonin levels in several herbs are in excess of 1000 ng/g. It is well known that normal average physiological plasma levels of melatonin are only 10-60 pg/mL. These high level-melatonin containing plants are traditionally used to treat diseases which presumably involve free radical damage. The current study provides new information concerning one potentially effective constituent present in a large number of medicinal herbs. The results suggest that these herbs should be reevaluated in reference to their nutritional and medicinal value.

Antioxidants↗

PubMed2003

Amyloid beta-protein stimulates the expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) in human cerebrovascular smooth muscle cells.

The accumulation of fibrillar amyloid-beta protein (A beta) in cerebral blood vessels, a condition known as cerebral amyloid angiopathy (CAA), is a key pathological feature of Alzheimer's disease and certain related disorders and is intimately associated with cerebrovascular cell death both in vivo and in vitro. Moreover, severe CAA leads to loss of vessel wall integrity and cerebral hemorrhage. Although the basis for these latter pathological consequences in CAA remains unresolved alterations in local proteolytic mechanisms may be involved. Here we show that pathogenic forms of A beta stimulate the expression of plasminogen activator activity in cultured human cerebrovascular smooth muscle (HCSM) cells, an in vitro model of CAA. RNase protection assays and plasminogen zymography showed that urokinase-type plasminogen activator (uPA) was responsible for this activity. There was preferential accumulation of uPA on the HCSM cell surface that was mediated through a concomitant increase in expression of the uPA receptor. In the presence of plasminogen there was robust degradation of A beta that was added to the HCSM cells resulting in restoration of cell viability. This suggests that increased expression of uPA may initially serve as a protective mechanism leading to localized degradation and clearance of the pathogenic stimulus A beta. On the other hand, chronic expression of uPA and plasminogen activation led to a profound loss of HCSM cell attachment. This suggests that a similar prolonged effect in vivo in the cerebral vessel wall may contribute to loss of integrity and cerebral hemorrhage in CAA.

Adult↗

PubMed2003

On-line hyphenation of capillary isoelectric focusing and capillary gel electrophoresis by a dialysis interface.

An on-line two-dimensional (2D) capillary electrophoresis (CE) system consisting of capillary isoelectric focusing (CIEF) and capillary gel electrophoresis (CGE) was introduced. To validate this 2D system, a dialysis interface was developed by mounting a hollow fiber on a methacrylate resin plate to hyphenate the two CE modes. The two dimensions of capillary shared a cathode fixated into a reservoir in the methacrylate plate; thus, with three electrodes and only one high-voltage source, a 2D CE framework was successfully established. A practical 2D CIEF-CGE experiment was carried out to deal with a target protein, hemoglobin (Hb). After the Hb variants with different isoelectric points (pIs) were focused in various bands in the first-dimension capillary, they were chemically mobilized one after another and fed to the second-dimension capillary for further separation in polyacrylamide gel. During this procedure, a single CIEF band was separated into several peaks due to different molecular weights. The resulting electrophoregram is quite different from that of either CIEF or CGE; therefore, more information about the studied Hb sample can be obtained.

Animals↗

PubMed2003

Separation of selected humic degradation compounds by capillary electrochromatography with monolithic and packed columns.

The separation of selected lignin/humic substance (HS) degradation compounds by capillary electrochromatography (CEC) with a methacrylate-based monolithic column and a conventional column packed with 5 microm octadecyl silica (ODS) particles is presented. The effects of organic modifier concentration, pH of the mobile phase, ionic strength, applied voltage, and temperature on the separation were investigated to determine the optimal separation conditions. With the increase of pH in the mobile phase, some of analytes start to ionize and both chromatographic partition and electrophoresis can play roles in separation simultaneously. Accordingly, different selectivity from high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) could be achieved. The performances of both kinds of columns were compared. The results showed that the peaks of compounds obtained on the former column were much wider than those on the latter one, although good separation efficiency of alkylbenzenes could be readily achieved; the most probable reasons for this behavior and method to solve this problem were briefly discussed. The CEC of a soil fulvic acid with a monolithic column produced partly resolved broad bands; by means of nuclear magnetic resonance (NMR) analysis a wide range of oxygen derived aromatic substitution patterns was found with prominent contributions from phenolic and carboxylic groups.

Benzopyrans↗