Enhanced selectivity and sensitivity for inorganic anions using an ion-pairing reagent and sample stacking in capillary zone electrophoresis with direct UV detection

Abstract.

In this paper, the use of an ion-pairing reagent to improve the separation selectivity of inorganic anions in CZE was demonstrated by the addition of tetramethylammonium hydroxide (TMAOH) to the electrolyte. The separation of inorganic anions (Cl^–, I^–, Br^–, NO₂ ^–, NO₃ ^– and SCN^–) was performed using co-electroosmotic flow (EOF) with direct UV detection at 185 nm. The parameters affecting the mobility of the tested anions and the EOF such as the electrolyte pH and concentration of TMAOH in the electrolyte were examined to optimise the separation conditions. In addition, sample-stacking techniques were investigated to improve detection sensitivity. Detection sensitivities were improved 5–13-fold using electrokinetic sample stacking. The detection limits ranged from 1–3 µmol L^–1. Finally, the proposed method was used for the separation of anions in groundwaters.