Large volume stacking using an EOF pump in NACE‐MS

Large volume stacking using an EOF pump (LVSEP) is realized for CE with ESI‐MS. In LVSEP of anions, the adverse effects of a long sample matrix plug were overcome by pumping the plug out of the separation capillary to the inlet vial using the EOF under a potential of reverse polarity. Therefore, it was necessary to supply a backup run buffer from the outlet end of the capillary, which was not trivial in most ESI‐MS configurations. We solved this difficulty simply by placing a vial supplying a backup run buffer during the matrix removal and sample stacking process. In addition, methanol was used as the run buffer solvent enabling a bare fused‐silica capillary to meet the requirement of suppressed EOF. This LVSEP CE/ESI‐MS has been successfully applied to six anionic analytes, achieving 400‐fold enrichment in the detection sensitivity by using a conventional sheath liquid CE/ESI‐MS interface without any physical modification.