Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Zero net-flow in capillary electrophoresis using acrylamide based hydrogel

Zero net-flow was observed when acrylamide based hydrogel was used in a vial at one end of a fused-silica capillary during electrophoresis with electroosmotic flow.

Highly charged polyelectrolyte coatings to prevent adsorption during protein and peptide analysis in capillary electrophoresis

Capillary electrophoresis (CE) is an interesting technique for protein and peptide analysis. However, one of the major problems concerns sample adsorption on the internal capillary wall. The use of non-covalent coatings using highly charged polyelectrolytes is an efficient, simple, and fast approach to reduce peptide and protein adsorption phenomena. We have studied in a systematic manner the effect of coating conditions on the stability and efficiency of multilayer coatings using poly(diallyldimethylammonium) chloride (PDADMAC) as polycation and polystyrene sulfonate (PSS) as polyanion. When optimal conditions defined in the protocols are used, very stable coatings are obtained and adsorption phenomena are eliminated. The coatings are stable over a large range of pH buffer (2-10) and in the presence of organic solvent. Hundreds of analyses can be performed without coating regeneration. Coated capillaries can be easily stored and reused.

Control of the EOF in CE using polyelectrolytes of different charge densities

The control of the EOF direction and magnitude remains one of the more challenging issues for the optimization of separations in CE. In this work, we investigated the possibility to use variously charged polyanions for a fine-tuning of the EOF using polyelectrolyte multilayers. For that purpose, polyanions of poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonate) (PAMAMPS) with different chemical charge rates varying between 3 and 100% were used. These copolymers are statistic hydrophilic copolymers of acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonate (AMPS). The study of the influence of the chemical charge rate (AMPS molar proportion in the copolymer) on the electroosmotic mobility (mu(eo)) of a capillary modified by a polyelectrolyte bilayer (polycation/PAMAMPS) revealed that the fine-tuning of the EOF was possible, at least for cathodic or slightly anodic EOF (micro(eo) from -5 x 10(-5) to +35 x 10(-5) cm(2)V(-1)s(-1)). Electroosmotic mobility values were compared with the free-draining electrophoretic mobilities of the PAMAMPS constituting the last layer of the capillary coating. The stability of the EOF is discussed in detail on the basis of successive determinations of electroosmotic mobility and migration times. The application to the separation of a model peptide mixture demonstrated the interest (and the simplicity) of this approach for optimizing resolution and analysis time. Experimental resolutions were compared to the theoretical ones that we would obtain on a fused-silica capillary having the same EOF as the coated capillary.

pH effect on dynamic coating for capillary electrophoresis of DNA

A buffer consisting of tris(hydroxymethyl)aminomethane, 2-(N-moropholino)ethanesulfonic acid (Mes) and EDTA with constant ion strength was used to investigate the effect of buffer pH on the dynamic coating behavior of poly(N-isopropylacrylamide) (PNIPAM) for DNA separation. The atomic force microscopy (AFM) image illustrated that PNIPAM in lower-pH buffer was much more efficient in covering a silica wafer than that in higher-pH buffer. The coating performance of PNIPAM was also quantitatively analyzed by Fourier transform IR attenuated total reflectance spectroscopy and by measuring the electroosmotic flow (EOF). These results indicated that the stability of the dynamic coating was dependent on the pH of the sieving matrix and was improved by reducing the pH to the weak-acid range. The lower pH of the sieving buffer may induce the polymer more efficiently to adsorb on the capillary wall to suppress EOF and DNA-capillary wall interaction for DNA separation. The enhanced dynamic coating capacity of PNIPAM in lower-pH buffer may be attributed to the hydrogen bonds between the hydroxyl groups of the silica surface and the oxygen atom of the carbonyl groups of PNIPAM.

Evaluation of surface roughness of hydrogels by fractal texture analysis during swelling

The surface of a biomaterial reacts in contact with biological fluids. Hydrogels are used to prepare biomaterials. The surface roughness of materials can be explored by several techniques. However, when considering hydrogels, the surface examined in the dry state does not reflect the final conformation. How the surface roughness is affected by swelling has been little explored by quantitative methods. We have evaluated the surface roughness of poly(2-hydroxyethyl methacrylate) (i.e., pHEMA) by image analysis. Images of disks, prepared from linear pHEMA, were obtained on a light microscope after various incubation times in saline. Fractal texture analysis was done on images to determine the fractal dimension D. In this study, D exhibited a significant decrease during swelling and was highly correlated with the swelling ratio (r2 = 0.994, p < 0.00001). Water uptake by the surface of the polymer affected the surface roughness. Image analysis using fractal algorithms appears to be the most interesting technique for the quantitative exploration of surfaces of hydrated materials that cannot be measured by conventional methods.