Electrophoretic effects of the adsorption of alkyl surfactants to PDMS

MARIA F. MORA; Y. DING; CARLA EUGENIA GIACOMELLI; CARLOS D. GARCIA

Chicago (EE.UU)

Conferencia; 58 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy; 2007

Capillary electrophoresis (CE) microchips have proven to be a very attractive analytical technique offering speed, small sample and solvent volumes, and low cost. Poly(dimethylsiloxane) (PDMS) is considered one of the most convenient materials to fabricate microchips. However, the hydrophobic nature of PDMS limits its applications. Different coating procedures have been used to reduce the hydrophobicity of PDMS. Among them, surfactant coatings are very popular because they adsorbs spontaneously on PDMS so the coating procedure is very simple.  In this work, the adsorption of alkyl surfactants on PDMS was studied performing electroosmotic flow measurements. For the EOF measurements, fused silica capillaries coated with PDMS were used. This approach allows measuring the EOF using standard CE instrumentation obtaining very reproducible results. It was observed that the EOF can be significantly affected by the addition of different surfactants at different concentrations. The adsorption profiles were obtained using alkyl surfactants with different chain length and different head groups. It was found that the longer the hydrophobic chain, the higher the affinity for the surface. On the other side, similar EOF values were obtained after the adsorption of surfactants with the same chain length. These results suggest that the interaction of surfactant/PDMS is mainly ruled by the hydrophobicity of the absorbate. The adsorption profiles were also studied using silanized and PDDA coated PDMS. The effect of different alkyl sulfates on the separation of phenolic compounds was also studied.