Advances in sol‐gel based columns for capillary electrochromatography: Sol‐gel open‐tubular columns

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Abstract
The development of sol‐gel open‐tubular column technology in capillary electrochromatography (CEC) is reviewed. Sol‐gel column technology offers a versatile means of creating organic‐inorganic hybrid stationary phases. Sol‐gel column technology provides a general approach to column fabrication for microseparation techniques including CEC, and is amenable to both open‐tubular and monolithic columns. Direct chemical bonding of the stationary phase to the capillary inner walls provides enhanced thermal and solvent stability to sol‐gel columns. Sol‐gel stationary phases inherently possess higher surface area, and thus provide an effective one‐step alternative to conventional open‐tubular column technology. Sol‐gel column technology is applicable to both silica‐based and transition metal oxide‐based hybrid stationary phases, and thus, provides a great opportunity to utilize advanced material properties of a wide range of nontraditional stationary phases to achieve enhanced selectivity in analytical microseparations. A wide variety of stationary phase ligands can be chemically immobilized on the capillary inner surface using a single‐step sol‐gel procedure. Sol‐gel chemistry can be applied to design stationary phases with desired chromatographic characteristics, including the possibility of creating columns with either a positive or a negative charge on the stationary phase surface. This provides a new tool to control electroosmotic flow (EOF) in the column. Column efficiencies on the order of half a million theoretical plates per meter have been reported for sol‐gel open‐tubular CEC columns. The selectivity of sol‐gel stationary phases can be easily fine‐tuned by adjusting the composition of the coating sol solution. Open‐tubular columns have significant advantages over their packed counterparts because of the simplicity in column making and hassle‐free fritless operation. Open‐tubular CEC columns possess low sample capacity and low detection sensitivity. Full utilization of the analytical potential of sol‐gel open‐tubular columns will require a concomitant development in the area of high‐sensitivity detection technology.