Capillary Electrophoresis Separations on a Planar Chip with the Column-Coupling Configuration of the Separation Channels

摘要

Some basic aspects of capillary electrophoresis (CE) separations on a poly(methyl methacrylate) chip provided with two separation channels in the column-coupling (CC) configuration and on-column conductivity detectors were studied. The CE methods employed in this study included isotachophoresis (ITP), capillary zone electrophoresis (CZE), and CZE with on-line ITP sample pretreatment (ITP—CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed, and electrophoresis was a dominant transport process in the separations performed by these methods. Very reproducible migration velocities of the separated constituents were typical under such transport conditions, and consequently, test analytes could be quantified by various 1TP techniques with 1—2% RSD. The CC configuration of the separation channels provides means for an effective combination of an enhanced load capacity of the separation system with high detection sensitivities for the analytes in concentration—cascade ITP separations. In this way, for example, succinate, acetate, and benzoate could be separated also in instances when they were present in the loaded sample (1.2 pL) at 1 mmoVL concentrations while their limits of detection ranged from 8 to 12 pmoVL concentrations. A well-defined ITP concentration of the analyte(s) combined with an in-column sample cleanup (via an electrophoreticaily driven removal of the matrix constituents from the sepa-ration compartment) can be integrated into the separa-tions performed on the CC chip. These sample pretreat-ment capabilities were investigated in 1W—CZE separations of model samples in which nitrite, phosphate, and flucg-ide (each at a 10 pmol/L concentration) accoml1~nied1atrix constituents (sulfate and chloride) at considerably higher concentrations. Here, both the concentration of the ana-lytes and cleanup of the sample were included in the ITP separation in the first separation channel while the second separation channel served for the CZE separation of the ITP pretreated sample and the detection of the analytes.