Ultrahigh pressure reversed-phase liquid chromatography in packed capillary columns

The use of extremely high pressures in liquid chromatography can improve the efficiency and reduce analysis time for columns packed with small particles. In this work, fused-silica capillaries with inner diameters of 30 mu m are slurry packed with 1.5 mu m nonporous octadecylsilane-modified silica particles. These columns are prepared in lengths up to 66 cm with packing pressures as high as 4100 bar (60 000 psi), Near the optimum now rate, columns generate as many as 300 000 theoretical plates for lightly retained compounds (k' < 0.5) and over 200 000 plates for more retained compounds (k' approximate to 2). These translate to plate heights (H-min) as low as 2.1 mu m. The pressures required to run at optimum flow rates are on the order of 1400 bar (20 000 psi). Analysis times at these pressures are on the order of 30 min (k' approximate to 2) and can be reduced to less than 10 min at higher than optimum now rates, Capacity factors are observed to increase linearly with applied pressure.