Second Chemiluminescence Behavior of Fe²⁺, Fe³⁺ and Cr³⁺ in the Luminal-KMnO₄ System

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A novel flow injection chemiluminescence (CL) method has been developed for the determination of three metal ions, namely Fe²⁺, Fe³⁺ and Cr³⁺, based on the second CL (SCL) signal of the mixture of luminal with KMnO₄ in a sodium hydroxide medium by the catalysis of Fe²⁺, Fe³⁺ or Cr³⁺. The possible CL mechanism of the systems, the influencing factors, and the optimum conditions for the reactions were investigated based upon the kinetic curve of the CL reaction, CL spectra, UV-visible spectra and some other experiments. Under the optimum conditions, the SCL intensity was directly proportional to the concentration of these metal ions in solution in the range of 0.10 - 100.00 mg l^-1 for Fe²⁺, 0.50 - 7.50 and 7.50 - 200.00 mg l^-1 for Fe³⁺, 0.01 - 0.25 and 0.25 - 10.00 mg l^-1 for Cr³⁺. The detection limits (3 σ/s) were 9.87 × 10^-6 g l^-1, 2.71 × 10^-6 g l^-1 and 5.25 × 10^-7 g l^-1 for Fe²⁺, Fe³⁺ and Cr³⁺, respectively.