Characterization of continuous electrophoretic separations in narrow channels coupled to small bore capillaries

Continuous electrophoretic separations in narrow channels have been carried out by coupling conventional capillary zone electrophoresis to open channel structures with rectangular cross sections. Presented here is an examination of the results of continuous separations conducted under various experimental conditions. The characterization is conducted using analysis of both continuous and plug injections of material into the channel, and the parameters used to analyze the separation are lateral dispersion, longitudinal dispersion, and signal intensity. Longitudinal dispersion indicates the amount of band broadening in the direction parallel to channel flow and, therefore, determines the spatial resolution of the separation. Lateral dispersion corresponds to band broadening perpendicular to channel flow and affects the accuracy with which the time of sample introduction into the channel can be determined. The results from these experiments indicate that (a) a cooled channel system provides better results when longer analyses are conducted, (b) a capillary step rate yielding a band introduction angle of 45 degrees relative to the direction of flow in the channel provides the best compromise between longitudinal and lateral dispersions (this value typically equals 0.9 s/25‐μm step for the system used in this research), (c) a capillary to channel linear velocity ratio of 3 to 5 yields improved signals relative to lower ratios due to more sample introduced (velocity ratios above this may lead to loss of spatial resolution), and (4) fast channel flows yield more symmetrically shaped bands than do slower flows due to more efficient transfer of material from the capillary‐channel junction into the channel. Detection limits of 41 μM are obtained with a linear range from 0.12 mM to 1.9 mM for laser induced fluorescence detection.