ON-COLUMN TRANSIENT AND COUPLED COLUMN ISOTACHOPHORETIC PRECONCENTRATION OF PROTEIN SAMPLES IN CAPILLARY ZONE ELECTROPHORESIS

Two strategies for the isotachophoretic preconcentration of samples were evaluated using a standard protein mixture as an example. In the first, on-column transient isotachophoretic migration permits the injection of relatively large volumes of sample into a commercial instrument. Depending on the composition, 30-50% of the column length can be filled with the sample while maintaining good resolution of the sample components. When proper electrolyte compositions are selected, the conventional single-column instrument can be used for an isotachophoretic sample preconcentration of 50-fold or more without any modification. In the second strategy, a coupled-column system was examined which, in principle, provides a higher degree of freedom in the selection of capillary zone electrophoretic running conditions and the possibility of injection-of higher sample volumes. The gain in detection level is at least a factor of 1000 in the coupled-column arrangement; however, the instrumentation is more complicated.