Electrokinetic removal of charged species from small sample volumes

Cationic or anionic molecules can be selectively injected from an aqueous mixture of charged and neutral species into a capillary by electrophoresis. Under stacking conditions, this selective field enhanced sample injection was studied here as a potential sample preparation technique for the clean-up or purification of microliter samples. As a simple demonstration, cationic small molecules were removed or extracted from a 100 μL sample mixture using a commercial capillary electrophoresis instrument. The extraction was monitored using an on-line UV detector. Results from the micellar electrokinetic chromatography analysis of treated and untreated sample revealed significant reduction of cationic species in the treated sample. The technique is essentially a sequence of field enhanced sample injection experiments in capillary electrophoresis.