Investigation of properties of copper, ferrous complexes with 1-(5-bromo-2-pyridylazo)-2-naphthol-6-sulphonic acid and application of substitution reaction in metallic complex to selective determination of trace amounts of metal

The report was the first to establish the new method for the selective determination of trace amounts of metal using the substitution reaction in metallic complex. The reactions between copper(II) and 1-(5-bromo-2-pyridylazo)-2-naphthol-6-sulphonic acid (BPANS) and between ferrous(II) and BPANS at pH 3.5 were studied. In absence of any masking reagent, the recommended method was selective in the determination of trace amounts of copper with Fe–BPANS complex as chromogenic reagent because copper(II) can substitute Fe from Fe–BPANS complex to form Cu–BPANS complex. The ordinary spectrophotometric method was unsuitable to the substitution reaction because the excess of Fe–BPANS complex had the high absorption and affected seriously the absorption of Cu–BPTANS complex. The spectral correction principle may eliminate the above influence to give the simple determination of the composition ratio, stepwise absorptivity (ε) and stability constant (K) of metal complex. For analysis of samples, the recovery of copper was between 96.5 and 106% with R.S.D. less than 5%.