EFFECT OF COLUMN DIAMETER ON PLATE HEIGHT IN HIGH-SPEED LIQUID-CHROMATOGRAPHY USING PELLICULAR AND PERFUSED PARTICLES IN PACKED CAPILLARIES

The purpose of this work was to examine column designs that allow for rapid separations by packed capillary liquid chromatography. Previous work with packed capillary columns with inner diameters (i.d.'s) of 20 to 150 mum revealed significantly reduced eddy diffusion broadening in these columns compared to larger bore columns. These results suggested that resistance to mass transfer dominates band broadening in microcolumns at high flow rates. Thus, it should be possible to attain rapid separations in capillaries by using pellicular or perfused particles which reduce resistance to mass transfer in the stagnant mobile phase. Furthermore, the use of capillary columns with small eddy diffusion effects should give better performance than larger bore columns packed with similar particles. To test these possibilities, the plate height of an unretained solute as a function of flow velocity was evaluated in columns with internal diameters of 50 to 250 mum packed with pellicular particles (8 and 15 mum diameter) and perfusion particles (10 and 20 mum diameter). Decreasing both column i.d. and column i.d. to particle diameter ratio (rho) were found to improve the performance of columns packed with pellicular particles; however, rho was the most important factor. Column i.d. and rho had no effect on the performance of perfusion particles within the range tested. However, the capillary perfusion columns had better performance than previously reported for larger bore perfusion columns. The best results were obtained for 8 mum pellicular particles inside 50 mum i.d. columns. These columns generated nearly 7,000 theoretical plates in 10 s. Further improvements should be possible by using smaller particles and smaller column internal diameters.