Bifunctional cryptand modifier for capillary electrophoresis in separations of inorganic/organic anions and inorganic cations

Abstract

The macrocyclic polyether cryptand-22 was employed as a bifunctional modifier to separate cations and anions via capillary electrophoresis. The remarkable cation complexing ability of cryptand-22 resulted in an improvement in the separation/resolution of several cations, e.g., K⁺, Na⁺ and NH₄⁺ ions, by capillary electrophoresis. Cryptand-22 was protonated as cryptand-2H²⁺ at pH < 7 and the protonated cryptand-22 was used as a capillary surface modifier to separate various organic/inorganic anions by capillary electrophoresis. This modifier treatment resulted in the electro-osmotic flow (EOF) and electrophoretic mobility of the anions being in the same direction, thereby giving a greater column efficiency. At pH <7, cryptand-22 is protonated and its behaviour is similar to that of quaternary ammonium salts which can form complexes with anions; in addition, the EOF is reversed. The effect of the eluent anion on the velocity of the EOF was also investigated; the maximum velocity of the EOF was obtained by using acetic acid as the eluent. The capillary electrophoresis system with the protonated cryptand modifier was successfully applied to the separation and determination of various inorganic anions, e.g., l^–, NO₃^–, SCN^–, BrO₃^–, IO₃^– and CrO₄^2–, and various carboxylate anions, e.g., p-nitrobenzoic acid, p-chlorobenzoic acid, p-hydroxybenzoic acid, benzoic acid and terephthalic acid.