Characterization of a sapphire-epoxy coating for capillary electrophoresis

A new procedure for coating capillaries for capillary electrophoresis applying a sapphire (alumina) containing epoxy resin was developed. Coated capillaries showed considerably reduced electroosmotic flow, and decreased the adsorption of proteins to the internal wall of the capillary. Coating is transparent down to 195 nm and can be used with advantage to analyze different kinds of substances, such as small cations and/or anions, and proteins.     

Brush-like copolymer as a physically adsorbed coating for protein separation by capillary electrophoresis

A brush-like copolymer consisting of poly(ethylene glycol) methyl ether methacrylate and N,N-dimethylacrylamide (PEGMA-DMA) was synthesized and used as a novel static physically adsorbed coating for protein separation by capillary electrophoresis for the first time, in order to stabilize electroosmotic flow (EOF) and suppress adsorption of proteins onto the capillary wall. Very stable and low EOF was obtained in PEGMA-DMA-coated capillary at pH 2.2-7.8. The effects of molar ratio of PEGMA to DMA, copolymer molecular mass, and pH on the separation of basic proteins were discussed. A comparative study of bare capillary with PEGMA-DMA-coated capillary for protein separation was also performed. The basic proteins could be well separated in PEGMA-DMA-coated capillary over the investigated pH range of 2.8-6.8 with good repeatability and high separation efficiency because the copolymer coating combines good protein-resistant property of PEG side chains with excellent coating ability of PDMA-contained backbone. Finally, the coating was successfully applied to the fast separation of other protein samples, such as protein mixture and egg white, which reveals that it is a potential coating for further proteomics analysis.     

超支化聚合物化学键合毛细管电泳柱的制备及其对蛋白质的分离行为

分别合成了以三羟甲基丙烷和季戊四醇为核的超支化聚(胺-酯),并对其进行了红外测定、羟值测定、粘度测定等表征。采用化学键合方法将其涂于毛细管内壁,并测定涂层柱的电渗流以及对碱性蛋白质的分离能力,结果表明,涂层柱能有效地抑制碱性蛋白质在毛细管内壁上的吸附,大大降低电渗流;以三羟甲基丙烷为核的超支化聚(胺-酯)涂层柱的塔板数达105/m,而以季戊四醇为核的超支化聚(胺-酯)涂层柱的分离柱效更高,塔板数达107/m。实验结果表明这两类涂层柱都具有较好的分离效果和稳定性。     

Graft copolymer composed of cationic backbone and bottle brush-like side chains as a physically adsorbed coating for protein separation by capillary electrophoresis

To stabilize electroosmotic flow (EOF) and suppress protein adsorption onto the silica capillary inner wall, a cationic hydroxyethylcellulose-graft-poly (poly(ethylene glycol) methyl ether methacrylate) (cat-HEC-g-PPEGMA) graft copolymer composed of cationic backbone and bottle brush-like side chains was synthesized for the first time and used as a novel physically adsorbed coating for protein separation by capillary electrophoresis. Reversed (anodal) and very stable EOF was obtained in cat-HEC-g-PPEGMA-coated capillary at pH 2.2-7.8. The effects of degree of cationization, PEGMA grafting ratio, PEGMA molecular mass, and buffer pH on the separation of basic proteins were investigated. A systematic comparative study of protein separation in bare and HEC-coated capillaries and in cat-HEC-g-PPEGMA-coated capillary was also performed. The basic proteins can be well separated in cat-HEC-g-PPEGMA-coated capillary over the pH range of 2.8-6.8 with good repeatability and high separation efficiency, because the coating combines good protein-resistant property of bottle brush-like PPEGMA side chains with excellent coating ability of cat-HEC backbone. Besides its success in separation of basic proteins, the cat-HEC-g-PPEGMA coating was also superior in the fast separation of other protein samples, such as protein mixture, egg white, and saliva, which indicates that it is a promising coating for further proteomics analysis.     

Stable neutral double hydrophilic block copolymer capillary coating for capillary electrophoretic separations

Quaternized diblock copolymer, poly(N‐methyl‐2‐vinylpyridinium iodide‐block‐ethylene oxide), was successfully used as a neutral, dynamic coating to suppress the electroosmotic flow. The block copolymer consisted of two polymers that were linked covalently together. The cationic block (poly(N‐methyl‐2‐vinylpyridinium iodide)) was bound efficiently to the negatively charged capillary wall via electrostatic interactions, and the hydrophilic block (ethylene oxide) stabilized the system and created a neutral capillary surface with ultralow electroosmotic flow (+2.0 ± 4.5 × 10^?10 m²/Vs). The main advantages of the coating were simple and fast preparation, easy regeneration and automation, and stable electroosmotic flow. To emphasize the potential of this type of coating its stability was measured at a wide pH range demonstrating a high stability in the pH range of 4.0–10.5 and lifetime up to 8 days. The successful studies carried out with beta‐blockers, basic proteins, and lipoproteins proved the suitability of the coating for the separation of different sized analytes. Furthermore, the neutral coating developed is useful in a wide range of protein analysis and biological interaction studies under physiological condition.     

Electrokinetic separation of peptides and proteins using a polyvinylamine-coated capillary with UV and ESI-MS detection

In order to accomplish the analysis of peptides and proteins by capillary electrophoresis, Lupamin, a high-molecular-weight linear polyvinylamine (PVAm) polymer, was introduced to modify the inner wall of fused-silica capillaries by physical absorption. Thanks to the high density of positively charged amino groups in Lupamin under acidic conditions, not only is a strong reversed electroosmotic flow generated in the coated capillary but the adsorption of analytes on the inner wall of the capillary is also efficiently eliminated. It has been demonstrated that the Lupamin-coated capillary can be used to advantage for the rapid analysis of amino acids, peptides, and proteins with good resolution and peak shape by capillary electrophoresis. In order to evaluate the basic feature of a Lupamin-coated capillary, electroosmotic flows generated by a Lupamin coating layer under different conditions including pH, coating time, concentration, and the composition of electrolytes on Lupamin-coated and uncoated capillaries were investigated. Furthermore, electrospray ionization-mass spectrometry (ESI-MS) detection was carried out for the analysis of amino acids and peptides.     

Automated coating procedures to produce poly(ethylene glycol) brushes in fused‐silica capillaries

Many bioanalytical methods rely on electrophoretic separation of structurally labile and surface active biomolecules such as proteins and peptides. Often poor separation efficiency is due to surface adsorption processes leading to protein denaturation and surface fouling in the separation channel. Flexible and reliable approaches for preventing unwanted protein adsorption in separation science are thus in high demand. We therefore present new coating approaches based on an automated in‐capillary surface‐initiated atom transfer radical polymerization process (covalent coating) as well as by electrostatically adsorbing a presynthesized polymer leading to functionalized molecular brushes. The electroosmotic flow was measured following each step of the covalent coating procedure providing a detailed characterization and quality control. Both approaches resulted in good fouling resistance against the four model proteins cytochrome c, myoglobin, ovalbumin, and human serum albumin in the pH range 3.4−8.4. Further, even samples containing 10% v/v plasma derived from human blood did not show signs of adsorbing to the coated capillaries. The covalent as well as the electrostatically adsorbed coating were both found to be stable and provided almost complete suppression of the electroosmotic flow in the pH range 3.4−8.4. The coating procedures may easily be integrated in fully automated capillary electrophoresis methodologies.     

Capillary isoelectric focusing with pH 9.7 cathode for the analysis of gastric biopsies

Capillary isoelectric focusing tends to suffer from poor reproducibility, particularly for the analysis of complex protein samples from cellular or tissue homogenates. This poor reproducibility appears to be associated with erratic variations in electroosmotic flow. One cause of electroosmotic flow variation is degradation of the capillary coating caused by the extremely basic solution commonly used during mobilization and focusing; this degradation of the capillary coating can be reduced by employing a CAPS mobilization buffer at pH 9. Another cause of variation is protein adsorption to the capillary wall, which causes an increase in electroosmotic flow. The effects of protein adsorption can be reduced by use of surfactants in the buffer and by employing an extremely low sample loading. We report the use of CAPS mobilization buffer in combination with an ultrasensitive laser-induced fluorescence detector for the reproducible analysis of ∼2 ng of protein from a Barrett's esophagus biopsy.     

Decreased protein peak asymmetry and width due to static capillary coating with hydrophilic derivatives of polydimethylacrylamide

We have recently described [1] a fast and simple method for the "adsorbed static" coating of capillaries in capillary zone electrophoresis (CZE) with epoxy-poly(dimethylacrylamide) (EPDMA). Protein CZE peaks in the EPDMA-coated capillaries exhibited a peak asymmetry similar to that obtained in capillaries with "covalent static" coating of polyacrylamide, suggesting a similar degree of adsorption of the protein onto the coating [2]. Instability of such coating at very low ionic strength and its stripping from the capillary in the presence of sodium dodecyl sulfate (SDS) also indicated a hydrophilic bonding of EPDMA to the silanol surface of the capillary, while its stripping in the CZE of "carboxylate-modified" polystyrene suggested a competition between carboxylate and EPDMA for the hydrophilic bonds to silanol. To test those propositions, a number of EPDMA-derived coating agents with increased hydrophilicity were synthesized. Of a number of the hydrophilic coating agents tested (Table 1) only two, 2% hydrolyzed EPDMA (HPDMA) hydrolyzed in sulfuric acid to effect the conversion of the epoxy groups to diols (Table 1, No. 38), and 20% EPDMA (Table 1, No. 44) exhibited for representative proteins a decreased peak asymmetry and width while the stability of the suppression of electroosmotic flow (EOF), and the stability of mobility in consecutive CZE runs was reduced relative to EPDMA. Coating agents which were more highly hydrophilic than those two (Table 1, No. 49) or less hydrophilic than 2% EPDMA (Table 1, Nos. 57, 53, 46) provided no stable static coating.     

Capillary Electrophoresis of Recombinant Human EPO

Capillary electrophoresis (CE) provides a new analytical tool for the separation of proteins, and almost all traditional modes of electrophoresis can be carry out in CE. But serious adsorption of proteins on capillary wall prohibited the proper separation. Three main approaches are used to overcome adsorption and control electroosmotic flow, (1) buffer of high or low pH,high salt concentration and additives, (2) pre-adsorption of neutral or charged macromolecules on the capillary wall and (3) chemically bonded coatings which are expected to give the best shield of silanol groups present on bare silica by vaious hydrophilic polymers. Capillaries coated with linear polyacrylamide represent the most successful approach available to date. Cross-linkage of polyacrylamide coating is desired to increase its stability.     

Electroosmotic flow controllable coating on a capillary surface by a sol-gel process for capillary electrophoresis

A simple coating procedure employing a sol-gel process to modify the inner surface of a bare fused-silica capillary with a positively charged quaternary ammonium group is established. Scanning electron microscopic studies reveal that a smooth coating with 1 to approximately 2 microm thickness can be obtained at optimized coating conditions. With 40 mM citrate as a running electrolyte, the plot of electroosmotic flow (EOF) versus pH shows a unique three-stage EOF pattern from negative to zero and then to positive over a pH range of 2.5 to 7.0. At pH above 5.5, the direction of the EOF is from the anode to the cathode, as is the case in a bare fused-silica capillary, and the electroosmotic mobility increases as the pH increases. However, the direction of the EOF is reversed at pH below 4.0. Over the pH range of 4.0 to 5.5, zero electroosmotic mobility is obtained. Such a three-stage EOF pattern has been used to separate six aromatic acids under suppressed EOF and to separate nitrate and nitrite with the anions migrating in the same direction as the EOF. The positively charged quaternary ammonium group on the coating was also utilized to minimize the adsorption problem during the separation of five basic drugs under suppressed EOF and during the separation of four basic proteins with the cations migrate in the opposite direction as the EOF. Also, the stability and reproducibility of this column are good.     

Cationic starch derivatives as dynamic coating additives for protein analysis in capillary electrophoresis

Positively charged starch derivatives were used to modify the inner surface of fused-silica capillaries by addition to running buffer, which were subsequently employed in capillary electrophoresis (CE). Capillaries coated with the cationic starch derivatives were shown to generate a stable, reversed electroosmotic flow (EOF) in the investigated pH range of 3-9. The presented coating procedure was fast, based on a simple rinsing protocol where the polymer created a physically adsorbed, cationic polymer layer. Among the additives studied, a quaternary ammonium starch derivative showed a fast EOF mobility and effectively suppressed the adsorption of proteins. The intra- and inter-day reproducibility of the coating referring to the EOF mobility were satisfactory with relative standard deviation (RSD) of 0.27 and 1.67%, respectively. The coating enabled separation of some protein mixtures including basic proteins within l3 min with efficiencies up to 280,000 plates/m. In addition, this cationic starch derivative possessed a good solubility (about 100mg/mL), and it does not significantly contribute to the background adsorption in the UV region of 190-400 nm.     

Modification of capillary electrophoresis capillaries by poly(hydroxyethyl methacrylate), poly(diethylene glycol monomethacrylate) and poly(triethylene glycol monomethacrylate)

Modification of capillary electrophoresis (CE) capillaries by poly(hydroxyethyl methacrylate) (poly(HEMA), poly(diethylene glycol monomethacrylate) (poly(DEGMA) and poly(triethylene glycol monomethacrylate) (poly(TEGMA), was studied. Methods based on physical adsorption of the modifier and on its chemical binding were compared on the basis of the electroosmotic flow (EOF) reproducibility, the EOF dependence on the pH, the symmetry of the peak of positively charged tyramine, the stability of the coating and the separation of standard and milk proteins in the modified capillaries. Reproducible coatings were obtained by chemical binding of the polymers to the capillary walls and by coating with a solution of a polymer, as also demonstrated by the atomic force microscopy.     

Dynamic Coating Agents in CE

In capillary electrophoresis (CE) dynamic coating agents are commonly used for manipulating or reversing electroosmotic flow (EOF) and suppressing adsorption of analytes by the silica surface. In this paper we review general aspects of dynamic coating in CE and discuss features and facts concerning formation of the EOF and determination of its magnitude.     

金纳米微粒修饰毛细管电泳分离蛋白质的研究

报道了金纳米微粒(Au NP)修饰毛细管电泳分离蛋白质的方法.采用物理吸附法将Au NP修饰在熔融石英毛细管内表面,制备成Au NP修饰毛细管.探讨了修饰剂Au NP的浓度对电渗流及蛋白质分离的影响.结果表明,Au NP修饰的毛细管能有效地抑制电渗流及蛋白质在毛细管内壁上的吸附,提高分离效率.在优化的实验条件下,实现了...     

碱性蛋白质毛细管电泳分离研究

碱性蛋白质毛细管电泳分离研究任吉存，邓延倬，程介克（武汉大学化学系分析测试科学系，武汉，４３００７２）关键词毛细管电泳，碱性蛋白质，吸附，精氨酸，赖氨酸蛋白质的吸附作用严重影响了毛细管电泳分离蛋白质的重现性［１］．为此，人们寻找各种途径来克服蛋白质的...     

Quaternary ammonium substituted agarose as surface coating for capillary electrophoresis

A novel positively charged polymer of quaternary ammonium substituted agarose (Q-agarose) has been synthesized and explored for use as a coating in capillary electrophoresis. The fast and simple coating procedure is based on a multi-site electrostatic interaction between the polycationic agarose polymer and the negatively charged fused-silica surface. By simply flushing fused-silica capillaries with hot polymer solution a positively charged, hydrophilic deactivation layer is achieved. The polymer surface provides an intermediate electroosmotic flow of reversed direction, over a range of pH 2-11, compared to unmodified fused-silica. The coating procedure was highly reproducible with an RSD of 4%, evaluated as the electroosmotic flow mobility for 30 capillaries prepared at 10 different occasions. The application of Q-agarose coated capillaries in separation science was investigated using a set of basic drugs and model proteins and peptides. Due to the intermediate electroosmotic flow generated, the resolution of basic drugs could be increased, compared to using bare fused-silica capillaries. Moreover, the coating enabled separation of proteins and peptides with efficiencies up to 300.000 plates m(-1).     

Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: propanol as background electrolyte solvent

Peak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate-co-N-vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm(-1) were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.     

Polymeric ionic liquid as a dynamic coating additive for separation of basic proteins by capillary electrophoresis

A simple and economical capillary electrophoresis method has been developed for the analysis of four model basic proteins by employing a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium) bromide, as the dynamic coating additive. When a small amount of PIL was present in the background electrolyte, a cationic coating on the inner surface of fused-silica capillary was established. These PIL modified capillaries not only generated a stable reversed electroosmotic flow, but also effectively eliminated the wall adsorption of proteins. Several important parameters such as the PIL concentration in the background electrolyte, pH values and concentrations of the background electrolyte were optimized to improve the separation of basic proteins. Consequently, under the optimum conditions, a satisfied separation of basic proteins with peak efficiencies ranging from 247,000 to 540,000 (plates m⁻¹) had been accomplished within 11 min. The run-to-run RSDs (n = 3) of the migration times for the four basic proteins were all less than 0.37%.     

Separation of peptides and proteins by capillary electrophoresis using acidic buffers containing tetraalkylammonium cations and cyclodextrins

A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated.