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.