Electro-osmotic and pressure-driven flow properties of frits for packed column capillary electrochromatography prepared from functionalised and bare silica packings

Changes in electro-osmotic flow (EOF) induced in an open fused silica capil lary by the introduction of a single packing retainer (referred to as a 'fr it' throughout the article) are investigated. Frits located in a 34.5 cm lo ng capillary close to the detection window, as used commonly in packed colu mn capillary electro-chromatography, were made by sintering silica based pa cking materials having varying functionalities (bare silica, ODS-silica, a strong cation exchange packing (SCX) and a strong anion exchanger (SAX) at 430 degrees C for 15 s. The contributions of such frits to the total EOF me asured in the capillary are discussed. Despite the high temperature of heat ing of the packing, sufficient residual functional groups remained on the f rit such that distinctively different EOF behaviour was observed for each t ype of packing. Frits made from materials providing negative surface charge s, such as silica, ODS-silica and SCX, increased the magnitude of the catho dic EOF compared to the open capillary. On the other hand, a substantial an odic EOF of -1.88 x 10(-8) m(2) V-1 s(-1) was produced by introduction of a single frit made from the SAX material. An explanation of this behaviour i s given, based on the hypothesis that the EOF generated by the frit determi nes the overall flow in the whole open capillary. The frit is considered to work as a pump and overrides the EOF generated at the capillary wall.