Optimization of the indirect fluorimetric detection for the simultaneous analysis of inorganic anions and polycharged organic anions by capillary electrophoresis

Abstract
Until now, fluorescein sodium salt has been used to generate the background signal for indirect fluorimetric detection of inorganic cations or mono-charged organic anions separated by Capillary Zone Electrophoresis (CZE). In this paper, we extend the use of fluorescein sodium salt to the simultaneous CZE analysis of inorganic anions (Cl^-, NO^-₂, NO^-₃, SO^2-₄, F^-) and polycharged organic anions (oxalate and citrate). The electroosmotic flow was reversed by using tetradecyltrimethylammonium bromide (TTAB) or hexadimethrine. The specific problems linked to the simultaneous utilization of fluorescein sodium salt and a positively charged capillary were studied and resolved by reducing the fluorescein/TTAB interactions and by optimizing the fluorophore concentration in the electrolyte. The study of reproducibility and the quantitative approach led to very good results. In such conditions the quantification of Cl^-, NO^-₃ and SO^2-₄, in different mineral and spring waters, has been successfully realized. In addition, the detection thresholds reached the range of one hundred to a few hundred ppb.