Electroosmotic flow assisted pseudophase to pseudophase microextraction for stacking in capillary zone electrophoresis

A stacking technique is proposed to improve the poor detection sensitivity of capillary zone electrophoresis (CZE) with UV detection. A long injection (e.g., 12.4 cm plug) of model anionic analytes prepared in a dilute solution of hexadecyltrimethylammonium bromide (CTAB) was enriched 26-34-x (compared to a typical or 2.1 mm sample injection) via the injection of a micellar solution of sodium dodecyl sulfate (SDS) prior to CZE separation. During sample injection, the CTAB formed a stationary pseudophase coating, which trapped the analytes at the inner walls of a fused silica capillary. The SDS micelles then released the CTAB admicelles via the formation of solution CTAB-SDS catanionic micelles during SDS plug injection and voltage application. As the SDS micelles moved through the sample zone, the formation of the catanionic micelles then released and accumulated the analytes at the front of the injected SDS zone. The stacking technique is called electroosmotic flow (EOF) assisted pseudophase to pseudophase microextraction because the EOF was essential for the formation of CTAB-SDS catanionic micelles for microextraction. Also, the CTAB and SDS aggregates are both pseudophases, which were used to retain and release the analytes from the capillary wall, respectively.