Online preconcentration and two‐dimensional separation of cationic compounds via hyphenation of capillary zone electrophoresis with cyclodextrin‐modified micellar electrokinetic capillary chromatography

A novel preconcentration/separation approach, which online combined CZE with CD‐modified MEKC, was developed for simultaneous enhancing resolving power and detection sensitivity. CZE with cation‐selective exhaustive injection and transient ITP preconcentration was used as the first dimension, from which the effluent fractions were further analyzed by CD‐modified MEKC acting as the second dimension. As the key to successful integration of CZE with MEKC, a new interface was designed and electroaccumulation focusing strategy was employed to avoid analyte band diffusion at the interface. The comprehensive 2‐D system was successfully established with only one high voltage and four electrodes. The grouping of two orthogonal separation techniques, together with analytes preconcentration techniques, significantly enhanced resolution and sensitivity for 2‐D separation of cationic compounds. The resulting electrophoregram was quite different from that of either single CZE or MEKC. Up to 14 000‐ to 35 000‐fold improvement in sensitivity was obtained relative to conventional electrokinetic injection method. The limits of detection (S/N=3) were in the range of 0.03–0.1 μg/L. The number of theoretical plates was in the range of 103 000–184 000. This method was successfully applied to the analysis of trace cationic cardiovascular drugs in wastewater.