Sol−Gel Column Technology for Single-Step Deactivation, Coating, and Stationary-Phase Immobilization in High-Resolution Capillary Gas Chromatography

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Abstract

A sol−gel chemistry-based novel approach to column technology for high-resolution capillary gas chromatography is described that effectively combines surface treatment, deactivation, coating, and stationary phase immobilization into a single step. In the conventional approach, these operations are carried out in separate steps that make column fabrication a time-consuming job. In the new approach, a cleaned fused silica capillary is filled with a sol solution of appropriate composition, and sol−gel reactions are allowed to go on inside the capillary for a controlled period, typically 15−60 min. A wall-bonded coating results due to condensation of the surface silanol groups with the sol−gel network evolving in their vicinity. Because of the direct chemical bonding to fused silica substrates, sol−gel coatings possess significantly higher thermal stability than conventional coatings. This is especially important for thick and/or polar stationary phase coatings that are difficult to immobilize. Scanning electron microscopic studies revealed that sol−gel coatings were characterized by roughened surfaces, providing a number of chromatographic advantages, including higher surface area and faster mass transfer kinetics. Sol−gel column technology does not require any free radical cross-linking procedures for stationary phase immobilization and easily avoids any undesirable changes in the stationary phase properties that might be associated with the cross-linking reactions used in conventional technology. Sol−gel-coated poly(dimethylsiloxane) and Ucon columns provided efficient separations for analytes from a wide polarity range, including free fatty acids, phenolic compounds, amines, aldehydes, ketones, alcohols, and diols that are prone to peak tailing due to adsorptive interactions with the column walls. This suggests excellent quality of column deactivation. The new technology provided at least a 10-fold reduction in column preparation time. The sol−gel approach is universal in nature and can be effectively applied to a wide range of microcolumn separation techniques.

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