Analysis of channel-geometry effects on separation efficiency in rectangular-capillary electrochromatography columns

A three-dimensional random walk model was developed to evaluate the impact of column geometry on separation efficiency in chromatography systems driven by electroosmotic flow. Contributions of injection plug length, cross-sectional area of channels, and aspect ratio of rectangular channels were examined in these simulation studies. Sample plug length had no impact on efficiency until it exceeded roughly 0.4% of the channel length. Plate height increased rapidly with increasing k′ as expected, almost doubling in going from k′=0.25 to 0.35. Channel geometry also had a major effect on efficiency. Plate height increased sharply in rectangular channel columns until the channel aspect ratio reached 4–8. But the effect of channel depth was even more dramatic. Minimum plate height (Hmin) was roughly half that of the channel depth in ideal cases. Hmin in a 10×2 μm channel was at 1.6 mm s−1. Rectangular channels comparable to those obtained by microfabrication are equivalent to packed column capillary electrochromatography columns in all cases.