Capillary electrophoresis separations on a planar chip with the column-coupling configuration of the separation channels

Some basic aspects of capillary electrophoresis (CE) separations on a poly( methyl methacrylate) chip provided with two separation channels in the colu mn-coupling (CC) configuration and on-column conductivity detectors were st udied. The CE methods employed in this study included isotachophoresis (ITP ), capillary zone electrophoresis (CZE), and CZE with on-line ITP sample pr etreatment (ITP-CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed, and electrophor esis was a dominant transport process in the separations performed by these methods. Very reproducible migration velocities of the separated constitue nts were typical under such transport conditions, and consequently, test an alytes could be quantified by various ITP techniques with 1-2% RSD. The CC configuration of the separation channels provides means for an effective co mbination of an enhanced load capacity of the separation system with high d etection sensitivities for the analytes in concentration-cascade HP separat ions. In this way, for example, succinate, acetate, and benzoate could be s eparated also in instances when they were present in the loaded sample (1.2 mu L) at 1 mmol/L concentrations while their limits of detection ranged fr om 8 to 12 mu mol/L concentrations. A well-defined ITP concentration of the analyte(s) combined with an in-column sample cleanup (via an electrophoret ically driven removal of the matrix constituents from the separation compar tment) can be integrated into the separations performed on the CC chip. The se sample pretreatment capabilities were investigated in ITP-CZE separation s of model samples in which nitrite, phosphate, and fluoride teach at a 10 mu mol/L concentration) accompanied matrix constituents (sulfate and chlori de) at considerably higher concentrations. Here, both the concentration of the analytes 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 th e analytes.