A transparent flow gating interface for the coupling of microcolumn LC with CZE in a comprehensive two-dimensional system

A new interface for the coupling of microcolumn highperformance liquid chromatography (micro-HPLC) with capillary zone electrophoresis (GZE) is presented. The new interface is based on the original now gated design developed in this laboratory but is now made from a clear plastic which allows for the direct observation and routine manipulation of the micro-HPLC and CZE capillaries, Ar, with the original design, a transverse flow of CZE buffer controls analyte injection onto the CZE capillary. To evaluate the reproducibility of the interface, 400 consecutive CZE separations of a mixture of fluorescein 5-isothiocyanate (FITC)-labeled phenylalanine and glutamic acid are performed over a 2 h period. The percent relative standard deviations (% RSD) of the peak height, peak area, and migration times of 400 nuns of FITC-phenylalanine are 2.5, 3, and 0.07%, respectively, and of FITC-glutamic acid are 2.5, 3.5, and 0.07%, respectively. The % RSDs of the peak height, peak area, and migration time were reduced to 0.7, 0.6, and 0.02%, respectively, by normalizing the results of glutamic acid to that of phenylalanine. This interface also introduces little extra-column band broadening into the system as evidenced by plate counts of 480 000 for FITC-phenylalanine and FITC-glutamic acid achieved ip less than 35 s, The clarity of the interface allows the flow gating and injection processes to be directly observed using a colored dye solution. Real-time images of an injection sequence using the interface have been acquired with the aid of video instrumentation and are presented to illustrate the injection process.