Simultaneous enrichment and separation of neutral and anionic analytes through combining large volume sample stacking...

In this work, we overcame the deficiencies of large volume sample stacking (LVSS) in separating low-mobility and neutral analytes through combining LVSS with sweeping in CE, and employed this new approach to enrich and separate neutral and anionic analytes simultaneously. This technique was carried out with pressure injection of large-volume sample followed by EOF as a pump pushing the bulk of low-conductivity sample matrix out of the outlet of the capillary while analytes were swept by micelles and separated via MEKC without the electrode polarity switching. Careful optimization of the enrichment and separation conditions allowed the enrichment factors (EFs) of peak height and peak area of the analytes to be in the range of 9-33 and 21-35 comparing with the conventional injection mode, respectively. The five analytes were baseline separated in 15 min and the detection limits ranged from 26.5 to 55.8 ng/mL (S/N = 3). The developed method was successfully applied to determine adenine, caffeine, theophylline, reduced L-glutathione (GSH) and oxidized L-glutathione (GSSG) in two different teas with recoveries that ranged from 84.4 to 105.2%.