Fluorescence properties of metal complexes of 8-hydroxyquinoline-5-sulfonic acid and chromatographic applications

Seventy-eight metal species are examined for fluorescence properties of their chelates with 8-hydroxyquinoline-5-sulfonic acid (HQS); 42 of these fluoresce, many intensely. The optimum pH, determined by ligand ionization vs. hydroxo complex formation, lies between 5 and 8. Cadmium forms the most fluorescent complex in a purely aqueous solution. Fluorescence is enhanced for many metals in surfactant (hexadecyltrimethylammonium ion, HTA/sup +/) containing media and in a water:dimethylformamide solvent. A number of metal ions quench the fluorescence of other metal-HQS chelates, Fe(III) being by far the most effective, and such quenching is accentuated in media containing HTA/sup +/. The fluorescence properties can be exploited by introducing the ligand through a postcolumn reactor or by incorporating it in the eluent in a chromatographic system. Subpicomole detection limits are attainable for Cd, Mg, and Zn.