Over 1000-fold improvement in an online preconcentration of trace anionic compounds by capillary electrophoresis with ionic liquid micelle-based three-step stacking.

A sensitive, simple, and environmentally friendly online three-step stacking strategy combining field-enhanced sample injection, sweeping and micelle to solvent stacking has been developed to determine trace amounts of organic anionic analytes in complex biological samples. A green ionic liquid, 1-dodecyl-3-methylimidazolium hydrogen sulfate, was first introduced as a micellar solution and used for electroosmotic flow reversal in this stacking strategy. The mechanism of stacking has been discussed, and parameters affecting three-step stacking preconcentration efficiency have been optimized. The capillary coated with an ionic liquid was easy to prepare, regenerable and repeatable (RSD<2.16%) and yielded a high efficiency. Under optimal conditions, the sensitivity improvement increased up to 2424-fold when compared with the normal capillary zone electrophoresis mode. The peak shape and separation efficiency of the model basic organic acids showed a significant enhancement when compared to traditional capillary zone electrophoresis. The optimized method showed great potential for quantitative analysis of trace concentration analytes in complex matrices.