Stability Constants of Cobalt(II) and Copper(II) Complexes with 3-[(o-Carboxy-p-nitrobenzene)azo]chromotropic Acid and Selective Determination of Copper(II) by Competition Coordination

Abstract

A method for selective determination of copper(II) based on the reactions of copper(II) or cobalt(II) with 3-[(o-carboxy-p-nitrobenzene)azo]chromotropic acid (CNBAC) at pH = 11.4 was developed. Results have shown that two complexes, Co(CNBAC)2 and Cu(CNBAC), were formed, whose cumulative stability constants were 5.22 × 109 and 7.61 × 105 dm3 mol–1, respectively, and their molar absorption coefficients were 1.19 × 104 and 2.12 × 104 dm3 mol–1 cm–1 at 610 nm. The competition coordination of CuII and CoII with CNBAC was applied for selective determination of CuII by the spectral correction technique. In the absence of any masking reagent, the recommended method was selective and was applied for quantitative determination of copper(II) in river and waste water samples