In this work, a facile approach was developed to modify a fused-silica capillary inner surface based on poly(dopamine) and poly(acrylamide) mixed coatings for protein separation by capillary electrophoresis. The surface morphology, thickness, and chemical components of poly(dopamine)/poly(acrylamide) mixed coatings on glass slides and silicon wafers were studied by atom force microscopy, ellipsometry, and X-ray photoelectron spectroscopy, respectively. The hydrophilicity and stability of the mixed coatings on glass slides were investigated by static water contact angle measurements. A comparative study of electroosmotic flow showed that the poly(dopamine)/poly(acrylamide) mixed coatings could provide effective suppression of electroosmotic flow. Meanwhile, the fast and efficient separations of the mixture of four alkaline proteins, the mixture of acidic, basic, and neutral proteins and egg white proteins were obtained by capillary electrophoresis. Furthermore, the consecutive protein separation runs and low RSDs of migration time demonstrated that these poly(dopamine)/poly(acrylamide) mixed coatings were capable of minimizing protein adsorption during the protein separation by using capillary electrophoresis.

To detect the quality of medicinal human albumin by capillary electrophoresis, we produced a fused-silica capillary coated with thermally cross-linked poly(vinyl pyrrolidone) to prohibit protein adsorption. This type of capillary was easily obtained by injecting an aqueous poly(vinyl pyrrolidone) solution into a fused-silica capillary and thermally annealing it at 200°C. Notably, stable and low electro-osmotic flow was obtained in the poly(vinyl pyrrolidone)-coated capillary at pH 2.20–9.00, and the separation of a mixture of four basic proteins indicated that the poly(vinyl pyrrolidone)-coated capillary exhibits excellent repeatability and separation efficiency; moreover, the separation of these four basic proteins could even be achieved at pH 7.00. The protein recovery percentage of human serum albumin in a single-protein solution and a mixed blood proteins solution was determined to be 97.03 and 95.40% in the poly(vinyl pyrrolidone)_50–3 (representing the concentration of the capillary-injected poly(vinyl pyrrolidone) aqueous solution, 50 mg/mL, and thermal annealing time, 3 h) capillary, respectively. Based on these results, we used the poly(vinyl pyrrolidone)_50–3-coated capillary to quantify the protein content of human albumin, and the results obtained from run to run, day to day and capillary to capillary demonstrated that the coated capillary could be used for quality testing commercially available human albumin.

Hydroxyethylcellulose-g-methoxypoly (ethylene glycol) (HEC-g-PEG) graft copolymers were synthesized through the etherification reaction between the hydroxyl group of hydroxyethylcellulose (HEC) and iodinated methoxypoly (ethylene glycol) (PEG-I), which was prepared on the basis of two-step reaction. Fourier transforms infrared spectrum (FTIR), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and iodide oxidation method were used to prove the success of synthesis of graft copolymer. Furthermore, the comparative studies of electro-osmotic flow (EOF) and protein separation in bare-fused silica, HEC and HEC-g-PEG-coated capillary were performed in capillary electrophoresis (CE). The results showed that HEC-g-PEG-coated capillary presented efficient EOF suppression ability and excellent resisting protein adsorption ability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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.

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.

Quasi-interpenetrating network (quasi-IPN) of linear polyacrylamide (LPA) with low molecular mass and poly(N,N-dimethylacrylamide) (PDMA), which is shown to uniquely combine the superior sieving ability of LPA with the coating ability of PDMA, has been synthesized for application in dsDNA and basic protein separation by CE. The performance of quasi-IPN on dsDNA separation was determined by polymer concentration, electric field strength, LPA molecular masses and different acrylamide (AM) to N,N-dimethylacrylamide (DMA) ratio. The results showed that all fragments in Φ×174/HaeIII digest were achieved with a 30 cm effective capillary length at –6 kV at an appropriate polymer solution concentration in bare silica capillaries. Furthermore, EOF measurement results showed that quasi-IPN exhibited good capillary coating ability, via adsorption from aqueous solution, efficiently suppressing EOF. The effect of the buffer pH values on the separation of basic proteins was investigated in detail. The separation efficiencies and analysis reproducibility demonstrated the good potentiality of quasi-IPN matrix for suppressing the adsorption of basic proteins onto the silica capillary wall. In addition, when quasi-IPN was used both as sieving matrix and dynamic coating in bare silica capillaries, higher peak separation efficiencies, and better migration time reproducibility were obtained.