Peak compression and resolution for electrophoretic separations in diverging microchannels

Abstract

We report the results of experiments and simulations on electrokinetic flow in diverging microchannels (with cross-sectional area that increases with distance along the channel). Because of conservation of mass and charge, the velocity of an analyte in the channel decreases as the channel cross-section increases. Consequently, the leading edge of a band of sample moves more slowly than the trailing edge and the sample band is compressed. Sample peak widths, rather than increasing diffusively with time, can then be controlled by the geometry of the channel and can even be made to decrease with time. We consider the possibility of using this peak compression effect to improve the resolution of electrophoretic separations. Our results indicate that for typical separations that are dispersion limited, this peak compression effect is more than offset by the decreased distance between peaks, and the separation resolution in diverging channels is worse than that found for straight channels at the same applied voltage. For separations in very short channels or at very high field strengths, however, when the separation efficiency is injection limited, the peak compression effect is dominant and diverging channels can then be used to achieve improved separation resolution.

Assessing Performance of Irregular Microvoids in Electrophoresis Separations

“…12 Boncinelli et al 13 used an agarose slab of steadily increasing thickness to generate a gradient of decreasing electric field strength which improved the resolution of DNA fragments. Ross et al 14 used diverging microchannels to reduce the effects of dispersion as they created a self-sharpening front on the analyte/solute band as it traveled down the channel. Straight and diverging microchannels were compared across the initial injection width of the dye as the primary factor for determining the best separation resolution.…”

Detecting deviations from pure EOF during CE separations

“…The leading edges are measured based on points of inflection as determined by the maximum and minimum in the first derivative. The second method uses the first statistical moment or center of gravity [30,31]. The computer algorithm employed in this analysis fits and subtracts the baseline fluorescence and then inte-grates the peak and identifies the midpoint of the integrated area.…”

Experimental Measurements of Critical Heat Flux in Expanding Microchannel Arrays

“…Along with novel research, some investigators have coined unhelpful terminology in the unfortunate term "diverging" [4,16,17]. The present authors politely contest this term as applied to a cross-section or to channels unless they truly do tend away from each other.…”