Determination of trace metal ions by capillary electrophoresis with fluorescence detection based on post-column complexation with 8-hydroxyquinoline-5-sulphonic acid Original Research Article

A method has been developed for the determination of aluminium and other metal ions (Ca, Mg, Zn, Cd) in aqueous samples. The metal ions are separated as the free cations by capillary electrophoresis. A solution of 8-hydroxyquinoline-5-sulphonic acid (HQS) is added post column to mix with the separation buffer. The resulting HQS complexes could be detected by their fluorescence. The influence of the pH of the separation buffer and the post-column reagent has been studied. For Al and Zn low-pH values were required, while for Ca and Mg a pH of 8–9 for the reagent was optimal. The fluorescence intensities could be increased approximately three-fold by adding 20% (v/v) dimethylformamide to the reagent. Under optimised conditions detection limits in the low μg l−1 level (approx. 0.1 μmol l−1) were obtained. The repeatability of the peak areas was from 1.4% at high concentration to 8.4% at a concentration of 0.25 μmol l−1. The speciation of aluminium ions in the presence of fluoride was studied.