Component complexation study of copper (II) and 2,7-bis(azo-2-hydroxy-3-sulpho-5-nitrobenzene)- 1,8-dihydroxynaphthaline-3,6-disulphonate salt

This article presents a study on the complexation of copper (II) with 2,7-bis(azo-2-hydroxy-3-sulfo5-nitrobenzene)-1,8-dihydroxynaphthalene-3,6-disulphonosodium salt (R) in the presence of diphenylguanidine (DPG), triphenylguanidine (TPG) and non-ionic SAA Triton X-114 (TX-114), carried out by spectrophotometric method. The optimal conditions for the Cu-R complexation are established as follows: pH=3 with the maximum light absorption of the complex occurring at a wavelength of 538 nm. The yield of the Cu-R complex reaches a maximum at the R component concentration of 8·10^-3 M, while the highest value for Cu-R-DPG complex is observed at concentrations of 8·10^-5 and 1·10^-3 M for the R and DPG components, respectively. The maximum of Cu-R-TFG is noted with concentrations of the R and TPG components comprising 8·10^-5 and 8·10^-4 M, respectively. The maximum yield of the Cu-R-TritonX-114 complex was obtained at a component concentration of 8·10^-5 and 8·10^-4 M, respectively. All complexes are formed immediately following the mixing of the component solutions and differ in stability. In the presence of a third component, the maximum absorption is observed at a wavelength of 512 nm (pH=1), 491 nm (pH=2) and 572 nm (pH=2) for the Cu-R-TX-114, Cu-R-DPG and Cu-R-TPG complex, respectively. The reaction ratio of components in the composition of homogeneous (Cu:R =1:2) and mixed ligand (Cu:R:X= 1:2:2) compounds is established. The interval of obedience to Beer's law equal to 0.12–2.32 mg/mL was determined for Cu-R complexes. For Cu-R-TX-114, Cu-RDPG and Cu-R-TPG, the determined interval comprised 0.07–2.32 mg/mL. The following values of stability constant for the complexes was established using the spectrophotometric method: 8.75±0.05 (Cu-R), 9.59±0.05 (Cu-R-TX-114), 9.85±0.05 (Cu-R-DPG) and 9.92±0.04 (Cu-R-TPG). The molar absorption coefficient of the complexes was determined as equal to 10400 (Cu-R), 15000 (Cu-R-TX-114), 15500 (Cu-R-DPG) and 16000 (Cu-R-TPG). The logK_hyd= 7.5, lgK_hyd= 12.7 and lgK_hyd= 13.9 constants of the nickel ion hydrolysis were obtained. The coefficients of the calibration curve equation are determined by the method of least squares. Under optimal complexation conditions, Cu-R was titrated with a component solution (TritonX-114, DPG and TPG) using the conductometric method. The effect of impurity ions and masking substances was studied. The determination of copper (II) is practically unhindered by alkaline, alkaline-earth and some transition elements, such as Ca (II), Ba (II), Mn (II), Cr (III), Sn (IV), Ga (III), In (III) and Zr (IV). The proposed express technique is characterised by its high sensitivity and selectivity, as well as being applicable for the determination of copper in food cereals. 

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