Pressure- and electroosmotically-driven flow in capillaries packed with nonporous particles for high-speed separations

The chromatographic performance of capillaries with 20 and 50 mu m inner di ameter (i.d.) packed with 4.5 and 3.0 mu m nonporous particles was evaluate d under conditions of pressure- and electroosmotically-driven flow for unre tained analytes with the goal of determining column configurations suitable for fast separations with both types of flow. Decreasing column diameter t o particle diameter ratio (rho) enhanced performance for pressure-driven fl ow but not for electroosmotically-driven flow. The improved performance wit h decreasing rho seen for pressure-driven flow was attributed to a decrease in the A term of the Knox equation. It was concluded that decreasing rho i n pressure-driven columns enhances the uniformity of the column, allowing f or improved performance; however, the use of electroosmotic flow masks hete rogeneous flow and thus no benefit in performance is seen from reducing rho . The best performance was with a 20 mu m i.d. column packed with 3.0 mu m particles. This column generated h(min) of 0.30 and 3,310 plates/s at the h ighest electroosmotic flow rate tested (reduced velocity of 41) whereas wit h pressure-driven flow the same column had h(min) of 0.96 and 1,200 plates/ s at the maximum flow velocity tested (reduced velocity of 29). (C) 1999 Jo hn Wiley & Sons, Inc.