Organically modified silicates as stationary phases for capillary electrochromatography

Capillary electrochromatography (CEC) is a microfluidic separation technique where the liquid flow is powered by an electric field instead of a pressure gradient. This mode of propulsion, reducing the dispersion of the analytes and leading to the absence of pressure drops, contributes to an increasing interest for CEC compared to pressure driven liquid chromatography. Efficient stationary phases need to be developed to promote a widespread use of CEC. Toward this goal, the present work describes the synthesis and the use of organically modified silicates (ormosils) as stationary phases for capillary electrochromatography. Ormosils, made by the sol-gel technique, consist of a silica framework containing organic materials. The chemistry of the sol-gel technique was studied in this work to control the resolutions, the efficiencies and the morphologies of the ormosil stationary phases. The factors affecting these parameters were defined and independently studied by electrochromatography and by electronic and optic microscopy. n-octyl modified silicates were chosen as stationary phases in the investigations and mixtures of polycyclic aromatic hydrocarbons (PAHs) were used as the test sample. Based on these results, methods were proposed for the formation of coatings and monoliths inside fused silica capillaries. The corresponding open tubular columns (OTCs) and monolithic columns (MCs) were studied with regard to their applications in CEC. Separations of PAHs, achieved with OTCs, were used to optimize the parameters acting during an electrochromatographic separation. Capillaries coated with ormosils containing different organic moieties were tested to separate several types of analytes. To miniaturize the CEC format, glass chips containing a capillary channel coated with ormosil stationary phases were used in electrochromatographic experiments. The difficulties of injection and detection systems were overcome by using commercial electrophoretic equipment.

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