The synthesis and applications of a new chromogenic and fluorescence reagent for cobalt(II)

Abstract

A new reagent, 5-(4-arsonicphenylazo)-8-(4-toluenesulfonamido)quinoline (APTSQ), was synthesised and its reaction with cobalt(II) and other metal ions was investigated. APTSQ was found to be a sensitive and selective reagent for the spectrophotometric and fluorimetric determination of trace amounts of cobalt. In the presence of cetyltrimethylammonium bromide, Co(II) reacts with APTSQ in basic medium to form a blue–violet complex in a molar ratio of 1:3. The maximum absorbance of the complex is at 582 nm with a molar absorptivity of 1.18×10⁵ l mol^–1 cm^–1. Beer’s law is obeyed for cobalt concentrations in the range 0–0.5 µg ml^–1. The interference of 34 substances was examined. In the presence of H₂O₂, cobalt reacts with APTSQ in solutions above pH 8.7, forming a product which shows intense fluorescence with λ_ex at 229, 287 and 331 nm and λ_em at 376 nm. The fluorescence intensity is proportional to concentration of cobalt in the range of 0–25 ng ml^–1. A detection limit (S/N = 3) of 0.002 ng ml^–1 was obtained. The mechanism of the fluorescence reaction was also investigated. The two proposed methods are precise, sensitive and simple and were applied to the determination of trace amounts of cobalt in mixtures, vitamin B₁₂ and vegetable samples.