pH-independent large-volume sample stacking of positive or negative analytes in capillary electrophoresis

In capillary electrophoresis, the short optical path length associated with on-column UV detection imposes an inherent detection problem. Detection limits can be improved using sample stacking. Recently, large-volume sample stacking (LVSS) without polarity switching was demonstrated to improve detection limits of charged analytes by more than 100-fold. However, this technique requires suppression of the electroosmotic flow (EOF) during the run. This necessitates working at a low pH, which limits using pH to optimize selectivity. We demonstrate that LVSS can be performed at any buffer pH (4.0-10.0) if the zwitterionic surfactant Rewoteric AM CAS U is used to suppress the EOF. Sensitivity enhancements of up to 85-fold are achieved with migration time, corrected area, and peak height reproducibility of 0.8-1.6%, 1.3-3.7%, and 0.8-4.9%, respectively. Further, it is possible to stack either positively or negatively charged analytes using zwitterionic surfactants to suppress the EOF.