CHARACTERIZATION OF CONTINUOUS ELECTROPHORETIC SEPARATIONS IN NARROW CHANNELS COUPLED TO SMALL-BORE CAPILLARIES

Continuous electrophoretic separations in narrow channels have been ca rried out by coupling conventional capillary zone electrophoresis to o pen 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 conduct ed using analysis of both continuous and plug injections of material i nto the channel, and the parameters used to analyze the separation are lateral dispersion, longitudinal dispersion, and signal intensity. Lo ngitudinal dispersion indicates the amount of band broadening in the d irection parallel to channel flow and, therefore, determines the spati al resolution of the separation. Lateral dispersion corresponds to ban d broadening perpendicular to channel flow and affects the accuracy wi th which the time of sample introduction into the channel can be deter mined. The results from these experiments indicate that (a) a cooled c hannel system provides better results when longer analyses are conduct ed, (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 va lue typically equals 0.9 s/25-mu m step for the system used in this re search), (c) a capillary to channel linear velocity ratio of 3 to 5 yi elds improved signals relative to lower ratios due to more sample intr oduced (velocity ratios above this may lead to loss of spatial resolut ion), 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 4 1 mu M are obtained with a linear range from 0.12 mM to 1.9 mM for las er induced fluorescence detection.