Study of the influence of the aspect ratio on efficiency, flow resistance and retention factors of packed capillary columns in pressure- and electrically-driven liquid chromatography

The influence of the aspect ratio, ρ (ρ = column diameter/particle diameter), on column parameters such as efficiency, retention factors and flow resistance was studied in both high-performance liquid chromatography and capillary electrochromatography with packed capillary columns. In order to compare the true efficiencies of different columns, a procedure to account for external band broadening was applied. High efficiencies (reduced plate height h ≈ 2) were obtained with capillary columns with internal diameters of 150-, 100-, and 75-μm, packed with 10-μm particles. In contrast to previous reports in the literature, no significant improvements in efficiency or flow resistance were observed when the aspect ratio of such columns was decreased. Our observations suggest that the wall effect in these types of columns is not significant. When the aspect ratio was decreased by increasing the particle size, a decrease in reduced plate height was observed. However, the results of flow resistance measurements showed that the latter effect should be attributed to differences in packing and particle batch quality rather than to differences in the aspect ratio.